4: Neurologic System

SECTION 4 Neurologic System



Section Editor: Marc Kent, DVM, DACVIM (Small Animal and Neurology)



Atlantoaxial Subluxation in Dogs

Botulism

Brachial Plexus Avulsion

Brain Tumors

Canine Distemper Neurologic Disease

Caudal Cervical Spondylopathy (Wobbler Syndrome)

Caudal Occipital (Chiari-like) Malformation and Syringohydromyelia

Degenerative Myelopathy

Discospondylitis

Fibrocartilaginous Embolic Myelopathy

Granulomatous Meningoencephalitis and Necrotizing Encephalitis

Head Trauma

Hydrocephalus

Idiopathic Facial Nerve Paralysis

Idiopathic Peripheral Vestibular Disease

Idiopathic Trigeminal Neuropathy

Intervertebral Disc Disease

Ischemic Brain Injury (Stroke)

Lumbosacral Disease, Degenerative

Myasthenia Gravis

Peripheral Nerve Sheath Tumors

Polyradiculoneuritis in Dogs, Acute

Seizures: Causes and Diagnosis

Seizures: Idiopathic Epilepsy

Seizures: Treatment

Seizures: Treatment of Resistant Cases

Spinal Cord Trauma

Spinal Tumors

Spondylosis Deformans

Steroid-Responsive Meningeal Arteritis

Tick Paralysis

Tremor Syndrome


Atlantoaxial Subluxation in Dogs


A. Courtenay Freeman, DVM


Marc Kent, DVM, DACVIM (Small Animal and Neurology)


Simon R. Platt, BVM&S, MRCVS, DACVIM (Neurology), DECVN



BASIC INFORMATION



Description


The spine is made up of small bones called vertebrae, which surround and protect the spinal cord. The first and second vertebrae in the neck are called the atlas and the axis, respectively. These vertebrae form the atlantoaxial (AA) joint, which is connected by ligaments. The second vertebra in the neck has a bony, finger-like projection (the dens) that extends into the first vertebra and provides further stabilization of the two vertebrae. AA subluxation is a partial dislocation of the two vertebrae. It occurs when the connection between the first and second vertebrae is unstable, and it usually results in compression of the spinal cord.



Causes


Typically, AA subluxation arises from a developmental problem or birth defect. In affected dogs the dens is absent or deformed, which results in an unstable joint. Additionally, some of the supporting ligaments may not form properly. AA subluxation can also occur as a result of trauma and disruption of the connection between these two vertebrae.


This condition is more common in toy and small-breed dogs, such as the Chihuahua and the Yorkshire terrier. Because it is usually a developmental problem, affected animals are typically young (less than 2 years old); however, older dogs may develop clinical signs later in life, particularly after trauma to the neck.



image Clinical Signs


Affected animals may have neck pain, an uncoordinated gait involving all four legs, and weakness. Clinical signs may develop after mild trauma, such as jumping or playing. The severity of clinical signs depends on the degree of spinal cord injury. Mild clinical signs include neck pain or an uncoordinated gait. More severely affected animals may be unable to walk. Severe spinal cord injury can affect the dog’s ability to breathe and can even result in death.



image Diagnostic Tests


AA subluxation may be suspected in young, toy breed dogs with compatible clinical signs. In many cases, a diagnosis can be made from x-rays of the neck that demonstrate an obvious dislocation of the vertebrae. X-rays must be obtained carefully to avoid further dislocation of the vertebrae. Magnetic resonance imaging (MRI) may be recommended to evaluate the spinal cord for compression and damage and to assess alignment of the vertebrae.



TREATMENT AND FOLLOW-UP




image Treatment Options


Medical and surgical treatments exist for dogs with AA subluxation. Although medical therapy can be effective, surgery is the preferred treatment in most animals.


Surgical treatment involves alignment and stabilization (fusion) of this joint:


• Stabilizing the AA joint prevents further spinal cord injury and allows the spinal cord to recover.

• The AA joint is fused by the placement of orthopedic implants (often wires or screws) into the small bones and application of surgical cement.

• Strict cage confinement is necessary after surgical stabilization to allow proper joint fusion and recovery of the spinal cord.

Medical therapy involves placing a splint around the head and neck of the affected animal to immobilize the AA joint:


• The splint usually stays in place for at least 8 weeks and periodically must be replaced.

• The splint immobilizes the AA joint for enough time to allow scar tissue to form and also helps stabilize the joint.

• Because the scar tissue may not be strong enough to stabilize the joint, these animals may re-injure their spinal cord at a later date.

• Strict cage confinement is necessary while the splint is in place and for an additional 4 weeks after its removal.

• Activity is restricted to short, controlled walks (with the dog in a body harness) that allow the animal enough time to urinate and defecate. Many small patients find it difficult to walk with the splint in place.

• The dog cannot be allowed to run, jump, or play during the confinement period.


image Follow-up Care


Animals with neck splints are often re-evaluated weekly, and the bandage or splint is changed. Follow-up visits are also needed frequently after surgery, and x-rays are usually done to evaluate healing 6-8 weeks after surgery. During the recovery period, notify your veterinarian immediately if any new neurologic signs develop or if previous ones recur or worsen.



Prognosis


Prognosis depends on the severity of the spinal cord injury and the treatment option pursued. Animals with mild clinical signs have a good prognosis. If clinical signs are severe, prognosis is variable and guarded (uncertain). Recurrence of signs is high with medical therapy, and surgical failure rates range from 10% to 40%.



SPECIAL INSTRUCTIONS:



Botulism


A. Courtenay Freeman, DVM


Marc Kent, DVM, DACVIM (Small Animal and Neurology)


Scott J. Schatzberg, DVM, PhD, DACVIM (Neurology)



BASIC INFORMATION



Description


Botulism is a rare disease that causes generalized weakness involving many of the nerves that activate the muscles of the body. Information travels down nerves to stimulate muscles to move (contract). This activation of muscles is mediated through a chemical called acetylcholine. Botulism blocks the release of acetylcholine from the nerve endings, which results in neurologic dysfunction and weakness.



Causes


Animals acquire botulism by ingesting the botulinum toxin, which is produced by a bacterial organism called Clostridium botulinum. This organism may be present in spoiled or rotting foods, garbage, and carrion.



image Clinical Signs


After the animal eats spoiled, contaminated material, vomiting and diarrhea may occur prior to the onset of neurologic signs, which typically occurs 2-4 days after ingestion of the botulinum toxin. Affected animals usually develop hind leg weakness that is rapidly followed by front leg weakness. The animal has difficulty standing and walking. It may stand crouched and have a short-strided gait. Severely affected animals may not be able to stand, lift their heads up, or even move their legs. They may not be able to eat or drink because of weakness of the jaw and tongue muscles. Affected animals may not be able to bark or vocalize as a result of weakness of the muscles of the larynx. They may not be able to blink their eyes.


As a consequence of weakness of the muscles of the esophagus, it may become weakened and dilated (megaesophagus). Food and water may be regurgitated and can be inhaled (aspirated) into the lungs, leading to pneumonia. Signs of aspiration pneumonia include a cough, fever, and difficulty breathing. In severely affected animals, muscles involved in breathing, such as the diaphragm, may become weak, leading to respiratory failure and death.



image Diagnostic Tests


A history of eating spoiled foods, garbage, or carrion and the presence of compatible clinical signs may cause an initial suspicion of botulism. Blood and feces can be tested for botulinum toxin; however, the toxin may not be detectable at the time clinical signs are occurring. Laboratory and other tests are needed to rule out diseases that cause similar signs. Chest x-rays may be recommended to look for pneumonia.


Specialized electrophysiologic procedures, such as electromyography and nerve stimulation testing, help to identify nerve dysfunction that supports the diagnosis. Sometimes the diagnosis can be made only after other diseases that cause similar clinical signs have been excluded.



TREATMENT AND FOLLOW-UP




image Treatment Options


There is no specific treatment for botulism. Affected animals usually require hospitalization and intensive supportive care, such as intravenous fluids, during recovery. Medications may be given to stop vomiting and help the diarrhea. Affected animals require clean, dry, padded bedding and frequent changes in their position to prevent bedsores and pneumonia. Assistance is needed with urination and defecation and keeping the animal clean. If the muscles of the diaphragm are involved, the animal may be placed on a mechanical ventilator.


Animals that are able to eat and swallow can be fed with the head held up to prevent aspiration. Animals unable to eat may require insertion of a feeding tube and supplemental nutrition. The eyes may require lubrication if the animal cannot blink. Physical therapy exercises can be performed to prevent muscle wasting and encourage improved muscle tone. Any secondary problems that arise because of this disease also require specific treatment.



image Follow-up Care


Recovery may be rapid in mild cases, but it can take weeks. After discharge from the hospital, continued nursing care is commonly needed at home. Recheck visits are often used to monitor the animal’s progress and recovery.



Prognosis


Clinical signs usually improve gradually over 3-4 weeks. Most mildly affected animals return to normal. Prognosis is very poor (guarded) for animals with paralysis of the breathing muscles and aspiration pneumonia.



SPECIAL INSTRUCTIONS:



Brachial Plexus Avulsion


A. Courtenay Freeman, DVM


Marc Kent, DVM, DACVIM (Small Animal and Neurology)


Simon R. Platt, BVM&S, MRCVS, DACVIM (Neurology), DECVN



BASIC INFORMATION



Description


The brachial plexus is a group of nerves located in the armpit area, where the front leg joins the shoulder blade and the chest. The brachial plexus on each side includes the nerves that activate muscle movement and allow for sensation (feeling) in the leg. A brachial plexus avulsion occurs when these nerves are completely torn. Sometimes the nerves are only damaged or stretched.



Causes


Trauma is the most common cause of brachial plexus injuries, and automobile accidents are the most common cause of trauma. Damage to the brachial plexus can also occur from falls, gunshot wounds, and other injuries that stretch the front legs.



image Clinical Signs


Clinical signs occur suddenly after the injury. Signs can vary depending on which nerves in the brachial plexus are damaged and the severity of the nerve damage.


• Damage to the nerves in one portion of the brachial plexus leads to inability to move the shoulder or bend the elbow. In these cases, the animal may be able to straighten the elbow and, therefore, support weight and walk.

• Damage to the nerves in another portion of the brachial plexus results in inability to support weight on the leg. The animal walks with the paw knuckled under and cannot bend the shoulder or elbow. Severe neurologic damage can result in loss of feeling in the leg.

A condition called Horner’s syndrome can also occur following brachial plexus avulsion. Horner’s syndrome affects the eye on the same side as the brachial plexus injury, resulting in a small pupil, a droopy upper eyelid, a raised third eyelid, and a sunken appearance to the eye. Vision is not affected.



image Diagnostic Tests


The diagnosis of brachial plexus avulsion is usually made from the history and neurologic examination. Other body systems are also evaluated for damage from the trauma. Orthopedic injuries and damage to the heart and lungs may be present and require immediate attention. X-rays of the front legs, abdomen, and chest may be recommended to evaluate for other injuries.


Specialized tests such as electromyography (EMG) and nerve conduction studies can be performed to evaluate muscle and nerve function; however, changes in these tests may not develop for 7-10 days after the injury. These tests usually require referral to a veterinary neurologist, are performed with the use of general anesthesia, and rarely provide information about the potential return of limb function.



TREATMENT AND FOLLOW-UP




image Treatment Options


There is no specific treatment for brachial plexus avulsion. If the nerves are only damaged and not torn, then recovery of function may be possible. Recovery can take weeks to months. During this time, it is important to prevent injuries to the affected leg caused by dragging of the toes. A foot protector or “bootie” may be recommended. Some severely affected animals may mutilate the affected leg, especially if they have lost sensation (feeling) in their toes. A drug called gabapentin may be tried to alleviate the “pins and needles” sensations that are associated with self-mutilation and foot chewing.


Physical therapy exercises may be recommended, such as massaging the muscles and moving the leg in a walking motion for a few minutes, several times a day. These exercises are essential to maintain muscle tone and prevent shrinkage of the muscles from disuse.


If the animal does not regain nerve function in the affected leg, amputation is usually recommended to prevent continued injury and self-mutilation.



image Follow-up Care


Initially, frequent follow-up examinations are often needed to monitor for improvement and further damage to the leg. Once nerve function returns, or if the leg is amputated, long-term follow-up is not typically necessary.



Prognosis


Prognosis depends on the severity of nerve damage. Mildly damaged nerves can sometimes regenerate over time, but the process is very slow. Brachial plexus injuries that cause paralysis and loss of feeling have a poor prognosis for recovery. Injuries that result in complete brachial plexus avulsions are irreversible. In general, if there is no improvement in 2-4 weeks, amputation of the affected leg may be necessary. The maximum time in which recovery is still possible is approximately 3-4 months after the injury.



SPECIAL INSTRUCTIONS:



Brain Tumors


A. Courtenay Freeman, DVM


Marc Kent, DVM, DACVIM (Small Animal and Neurology)


Simon R. Platt, BVM&S, MRCVS, DACVIM (Neurology), DECVN



BASIC INFORMATION



Description


Brain tumors (sometimes called neoplasms) may affect both dogs and cats. They may be benign or malignant. These tumors may arise from brain tissue (called primary tumors), grow into the brain from nearby areas of the head (such as the skull), or spread to the brain from another site in the body (metastatic tumors). The latter two types are called secondary tumors.


Brain tumors occur more frequently in older dogs and cats; however, on rare occasions, young animals can be affected. Commonly affected breeds include the golden retriever, Labrador retriever, collie, Boston terrier, and boxer. The domestic shorthair is the cat most commonly affected.



Causes


The cause of most brain tumors is unknown, but several types of tumors exist:


• The most common brain tumor in dogs and cats is the meningoma, which develops from the tissue that covers the brain and spinal cord (the meninges).

• The most common tumors that develop from tissue within the brain are gliomas, which can be classified as astrocytomas or oligodendrogliomas.

• Sometimes, tumors form from cells lining the ventricles (cavities within the brain that are filled with cerebrospinal fluid). Examples of these tumors include choroid plexus tumors and ependymomas.

Secondary tumors that arise in the nose, sinuses, skull, ears, or eyes may invade the brain. Cancer in other areas of the body can spread (metastasize) to the brain.



image Clinical Signs


Signs vary with the location and size of the tumor. Neurologic signs may develop gradually over weeks to months or arise suddenly. Common clinical signs include seizures, behavioral changes, loss of vision, and abnormalities in gait. As tumors enlarge the flow of cerebrospinal fluid (CSF) can become obstructed, causing signs of secondary hydrocephalus. (See also the handout on Hydrocephalus.)



image Diagnostic Tests


A neurologic examination, laboratory tests, and x-rays are often recommended to rule out other diseases that produce similar signs and to search for tumors elsewhere in the body. Imaging of the brain via computed tomography (CT scan) or magnetic resonance imaging (MRI) usually reveals a mass in the brain suggestive of a tumor but may not provide a specific diagnosis. A brain biopsy may be required to confirm the diagnosis. Biopsy samples are sometimes obtained during surgery or by guiding a needle into the tumor during the CT scan.


A spinal tap and collection of CSF for analysis may be recommended to eliminate other brain diseases, such as inflammation, but this can be risky in some patients with elevated CSF pressure in the brain.



TREATMENT AND FOLLOW-UP




image Treatment Options


Treatment options vary depending on the type and location of the tumor and the clinical signs produced. Surgery, radiation therapy, medical management, or a combination of these may be pursued.


Medications that may be administered include anticonvulsant drugs to control seizures and steroids to decrease inflammation and edema associated with the tumor. Although these medications do not affect the growth of the tumor, they can improve clinical signs and the animal’s quality of life. Chemotherapy may be beneficial for certain brain tumors but has not been as successful as surgery or radiation therapy.


Surgery can be performed on tumors in certain regions of the brain. Because they arise from the tissue covering the brain, meningiomas are often amenable to surgery. Surgery may allow removal of most of the tumor and relieve clinical signs. Although most animals recover well from brain surgery, serious risks exist, including worsening of clinical signs and death.


Radiation therapy can be used for tumors that are inoperable or to destroy tumor cells left behind from surgery.



image Follow-up Care


Frequent recheck visits are needed when therapy is initially started, to monitor for complications after surgery and to adjust medication dosages. Radiation therapy typically requires several weeks of treatment, followed by recheck visits about every 2 months. Continuous, long-term follow-up is needed for most patients with brain tumors.



Prognosis


Long-term prognosis for animals with a brain tumor is always very poor. Prognosis is affected by tumor type and location. Some cats with meningiomas may live 2-3 years after surgery, and dogs with meningiomas may survive for months or longer. It is not always possible to surgically remove the entire tumor in most dogs. Consequently, radiation therapy may be used after surgery to extend the survival time of affected animals. Without treatment, clinical signs in most animals worsen over several weeks. Most secondary tumors are cancerous, are very difficult to treat, and carry the worst prognosis.



SPECIAL INSTRUCTIONS:



Canine Distemper Neurologic Disease


A. Courtenay Freeman, DVM


Marc Kent, DVM, DACVIM (Small Animal and Neurology)


Scott J. Schatzberg, DVM, PhD, DACVIM (Neurology)



BASIC INFORMATION



Description


Canine distemper is a contagious viral infection of dogs that may cause respiratory, urogenital, gastrointestinal, ocular (eye), and central nervous system (brain and spinal cord) signs. The routine use of vaccines against canine distemper has greatly reduced the incidence of this disease in North America, but it still commonly occurs in many other parts of the world.



Causes


Canine distemper virus (CDV) is transmitted between dogs primarily through infected respiratory secretions. The virus multiplies within the lymph nodes (glands) of the head and throat. Infected white blood cells leave the lymph nodes and spread the infection throughout the body. Within 1 week, infection may involve the eyes, nose, intestinal and respiratory tracts, and the nervous system.


Unvaccinated puppies are most susceptible to CDV infection; however, older dogs may also become infected. The infection weakens (suppresses) the immune system, making the animal more susceptible to other diseases. Although vaccination is extremely effective for preventing CDV infection, occasionally animals become infected despite having been vaccinated.



image Clinical Signs


Clinical signs are variable and depend on the strength of the dog’s immune system. Vaccinated dogs with a strong immune system typically clear the virus and do not develop clinical signs. Dogs with a weak immune system, such as puppies, are often unable to fight off the infection and may develop severe clinical signs. Since it is not possible to determine the strength of a dog’s immune system, care should be taken to prevent exposure of potentially susceptible dogs.


Some affected dogs only develop generalized (systemic) signs, whereas others have only nervous system signs. Initially, signs of a respiratory infection may occur, with severe ocular and nasal discharge, cough, and fever. The respiratory infection can progress to pneumonia in some animals. Additional signs include loss of appetite, vomiting, and diarrhea.


Nervous system signs include mental dullness, lethargy, unresponsiveness, disorientation, blindness, imbalance, and seizures. Affected dogs may stumble as they walk and some act as if they are in pain.


Telltale physical findings can indicate a previous infection, such as abnormal enamel on the teeth, thickened skin on the nose and footpads (hyperkeratosis), and involuntary, rhythmic jerking of one or more muscles (myoclonus). Typically, myoclonus is confined to a single limb. The muscles of the head can be affected, however, and the animal may rhythmically clench its teeth. Myoclonus may persist even when the animal is sleeping.



image Diagnostic Tests


Routine laboratory tests are usually recommended to search for evidence of an infection and other organ involvement. CDV can cause a decrease in the white blood cell count. X-rays of the chest may reveal pneumonia.


Many tests can be used to diagnose CDV infection, but no single test is 100% diagnostic, so multiple tests are often needed. Samples that can be tested for CDV include the conjunctiva (tissue lining of the inside of the eyelids), skin biopsies, blood, cerebrospinal fluid (CSF, taken by spinal tap), and urine. Blood can also be tested for antibodies to CDV (canine distemper titer); however, this test can be difficult to interpret, because most animals produce antibodies after they are vaccinated.


Analysis of CSF may indicate evidence of inflammation in the nervous system of some dogs, but these changes are not specific for CDV infection and may not be seen in the early stages of the disease. Magnetic resonance imaging (MRI) can show multiple abnormal areas in the brain that are consistent with CDV infection.



TREATMENT AND FOLLOW-UP




image Treatment Options


There is no specific treatment for distemper infection. Supportive care is important for animals that are systemically ill. Anticonvulsant medications may be given for seizures, but the seizures can be difficult to control. (See also the handout on Canine Distemper Virus.) Affected dogs must be kept isolated from other dogs, because the disease is contagious.



image Follow-up Care


Many dogs require hospitalization for supportive care. Laboratory tests and x-rays may be repeated to monitor response to treatments. Recovery time can be prolonged, and recheck visits are often needed following discharge from the hospital. If the animal survives the acute infection, late-developing signs may still occur.



Prognosis


Prognosis is poor if the clinical signs are severe or worsen despite supportive care. CDV causes severe debilitation and death in many dogs; however, the disease is not fatal to all dogs. Dogs that develop neurologic signs have a worse prognosis. Neurologic signs, such as seizures, blindness, and myoclonus, may persist after recovery from infection. The disease is best prevented with appropriate vaccination.



SPECIAL INSTRUCTIONS:



Caudal Cervical Spondylopathy (Wobbler Syndrome)


A. Courtenay Freeman, DVM


Marc Kent, DVM, DACVIM (Small Animal and Neurology)


Scott J. Schatzberg, DVM, PhD, DACVIM (Neurology)



BASIC INFORMATION



Description


Caudal cervical spondylopathy (also called cervical vertebral malformation-malarticulation or wobbler syndrome) is a disorder that results in spinal cord compression due to instability of the spine. The spinal cord compression can be dynamic, which means the compression is worse when the neck is held in certain positions. The syndrome is most common in large- and giant-breed dogs.



Causes


Although the cause of wobbler syndrome is unknown, many factors may be involved. Compression may occur from bony malformation of the vertebrae, intervertebral disc herniation, or thickening of the supporting ligaments of the spine. The Doberman pinscher and Great Dane are the breeds most commonly affected. Great Danes are often affected before 2 years of age, whereas Dobermans are more commonly affected from 3-9 years of age.



image Clinical Signs


Signs depend on the speed of onset, duration, and degree of compression. Signs may develop suddenly over a few days or slowly over weeks to months. Typically, all four legs are affected because the problem involves the neck region. Occasionally, signs begin in the hind legs, but over time the disease usually affects all four legs. Neurologic abnormalities depend on the severity of spinal cord compression:


• Mild compression may result in neck pain only.

• More severe compression causes an uncoordinated (“wobbly”) gait in all four legs, crossing over of the legs when walking, toe scuffing, and weakness. The hind legs are often more affected than the front legs.

• As compression worsens, the animal may be unable to walk or may become paralyzed.


image Diagnostic Tests


The syndrome initially is suspected based on the history and clinical signs. X-rays of the neck may show degenerative changes in the spine; however, they cannot demonstrate spinal cord compression. Advanced imaging of the spine, such as magnetic resonance imaging (MRI), computed tomography (CT scan), or myelography (x-rays taken after a dye is injected into the space around the spinal cord) is necessary for the diagnosis. MRI provides the most detailed evaluation of the spinal cord and spine. Images may be obtained with the neck held in several positions. Your veterinarian may also recommend laboratory tests to rule out diseases that cause similar signs.



TREATMENT AND FOLLOW-UP




image Treatment Options


Conservative and surgical treatment options exist for dogs with wobbler syndrome. Conservative therapy is reserved for animals with pain and/or mild neurologic abnormalities and consists of exercise restriction, anti-inflammatory drugs, and pain medications.


• Exercise restriction involves strict confinement and limited leash walking, for the sake of urination and defecation only.

• Dogs should not be allowed to run, jump, or play during the period of confinement.

• Exercise restriction typically lasts 4-6 weeks and is followed by gradual return to normal activity over an additional month.

• Anti-inflammatory drugs, such as nonsteroidal anti-inflammatory medications or short-term corticosteroids, can be used, but they are not used together because of their combined side effects.

Surgery is often preferred for dogs with severe neurologic signs, such as moderate to severe incoordination, weakness, inability to walk, and paralysis, and for dogs with pain that is unresponsive to conservative treatment. Surgery may also be considered in dogs that have recurrent signs. Surgery may involve removal of herniated intervertebral disc material (common in the Doberman pinscher). It may also involve removal of various portions of the vertebrae that are compressing the spinal cord and spinal stabilization (fusion). Various techniques can be used to stabilize the spine. After surgery, conservative therapy is also usually started.



image Follow-up Care


Initially, repeated neurologic examinations are often performed to monitor for improvement in clinical signs. These examinations can be performed daily if the dog is hospitalized or periodically during outpatient visits. Visits are often repeated every 1-2 weeks initially and then decreased to every 1-2 months if improvement is observed. Long-term follow-up is frequently needed. Notify your veterinarian if any signs worsen or recur.



Prognosis


Prognosis depends on the severity and duration of the clinical signs. Mildly affected dogs and dogs that have pain as the only clinical sign often respond well to conservative therapy. Many dogs with moderate to severe clinical signs improve after surgical therapy. Resolution of clinical signs may take weeks to months. Prognosis is worse for dogs with severe neurologic signs and for dogs with multiple areas of compression of the spinal cord. Dogs with severe clinical signs have a very poor (guarded) prognosis even with surgery. Clinical signs may recur in dogs managed both conservatively and surgically.



SPECIAL INSTRUCTIONS:



Caudal Occipital (Chiari-like) Malformation and Syringohydromyelia


A. Courtenay Freeman, DVM


Marc Kent, DVM, DACVIM (Small Animal and Neurology)


Simon R. Platt, BVM&S, MRCVS, DACVIM (Neurology), DECVN



BASIC INFORMATION



Description


The skull is made up of several flat bones that fuse together to encase and protect the brain. The bone of the back of the skull is called the occipital bone. Malformation or abnormal development of this bone compresses the back part of the brain, which is called the cerebellum. This compression causes the cerebellum to herniate (shift backward) and obstruct the hole in the skull where the brain joins the spinal cord. This hole is called the foramen magnum.


Obstruction of the foramen magnum alters the flow of cerebrospinal fluid (CSF). Normally, CSF is produced within the brain and flows around the brain and down the outside of the spinal cord. In caudal occipital or Chiari-like malformation, obstruction of CSF flow leads to the accumulation of fluid within the spinal cord. This fluid accumulation is referred to as syringohydromyelia (SHM).


The Cavalier King Charles spaniel is the most commonly affected breed of dog; however, other dogs, especially small-breed dogs, can also be affected.



Causes


Caudal occipital malformation is a congenital problem caused by abnormal development of the occipital bone of the skull. In the Cavalier King Charles spaniel, the condition may be inherited.



image Clinical Signs


Onset of clinical signs may be sudden or may take several months to years to develop. Animals affected by this disease range from young to old.


Clinical signs often result from SHM and are related to spinal cord dysfunction. Signs include neck pain, weakness, incoordination, and muscle loss over the shoulders. Scoliosis (abnormal curvature of the spine) and twisting of the head can occur. Affected animals may excessively scratch at their head and neck, especially when excited. Facial muscle paralysis and imbalance are occasionally observed. Seizures have also occurred in some affected animals, but they may be unrelated to this malformation.



image Diagnostic Tests


A neurologic examination, routine laboratory tests, and x-rays are often recommended to rule out other diseases that produce similar signs. Confirming the diagnosis usually requires magnetic resonance imaging (MRI). MRI can reveal distortion of the brain structures, obstruction of CSF flow at the foramen magnum, and the presence of SHM.



TREATMENT AND FOLLOW-UP




image Treatment Options


Medical and surgical treatments exist. In most cases, medical therapy is pursued initially and is aimed at decreasing CSF production and providing pain relief. Corticosteroids can be used to reduce CSF production. Occasionally, diuretic drugs may also be needed. Pain medications, such as gabapentin or tramadol, may be used in animals that experience discomfort or painful episodes.


Surgical therapy involves enlarging the foramen magnum in an attempt to restore CSF flow. When the obstruction is relieved, the CSF does not continue to accumulate within the spinal cord. This surgery may not eliminate fluid that has already accumulated, so some clinical signs may not improve. Surgery is most often considered for dogs with severe signs or signs that worsen despite medical therapy.



image Follow-up Care


Follow-up visits are scheduled frequently at first, to monitor the success of medical or surgical treatment. Recheck appointments may eventually be decreased to every 6 months if the animal responds to treatment and has no complications. A recheck MRI may be helpful to evaluate the success of treatment and to identify any progression of the disease.



Prognosis


Prognosis depends on the severity of clinical signs and the extent of structural damage to the brain and spinal cord. Many mildly affected dogs can be successfully treated with medical therapy. In some dogs clinical signs improve after surgery, but surgery is not always successful, and recurrence of signs is possible. In some dogs, surgery may halt worsening of the signs and allow medical therapy to be more effective.



SPECIAL INSTRUCTIONS:



Degenerative Myelopathy


A. Courtenay Freeman, DVM


Marc Kent, DVM, DACVIM (Small Animal and Neurology)


Scott J. Schatzberg, DVM, PhD, DACVIM (Neurology)



BASIC INFORMATION



Description


Degenerative myelopathy is a spinal cord condition that results in progressive hind leg weakness and incoordination. The spinal cord is composed of nerve cells and fibers (axons). Nerve impulses are transmitted along the axons of the spinal cord from the brain to the limbs, and vice versa. When portions of the spinal cord degenerate, nerve impulses are not properly transmitted in both directions. Consequently, the legs become weaker, and eventually the dog cannot voluntarily move them. Feeling in the legs is also affected. The degeneration involves primarily the spinal cord in the back region, so the hind limbs of the dog are predominantly affected.



Causes


The exact reason degenerative myelopathy develops is not well understood. An inherited (genetic) basis is suspected. The German shepherd dog is the most commonly affected breed, but any large-breed dog may develop the condition. Other breeds commonly affected include the boxer and Pembroke Welsh corgi. The myelopathy usually occurs in older dogs (older than 5 years).



image Clinical Signs


Degenerative myelopathy causes a chronic, progressive, nonpainful hind leg weakness.


• Affected animals become uncoordinated (unsteady) in the hind legs, scuff or knuckle over on those toes, stumble, and have difficulty rising from a down position.

• Eventually, the disease worsens to the point where the dog can no longer walk and drags its hind legs.

• Loss of voluntary control of urination, fecal incontinence, and front leg weakness may occur late in the disease.


image Diagnostic Tests


Currently, there is no definitive test for degenerative myelopathy. Routine laboratory tests may be recommended but are usually normal. A presumptive diagnosis can be made when advanced imaging studies reveal no abnormalities of the spinal cord or vertebral canal. In other words, advanced imaging rules out other diseases that can cause similar signs. The best imaging technique for this purpose is magnetic resonance imaging (MRI), but myelography (x-rays taken after insertion of a dye around the spinal cord) and computed tomography (CT scan) can also be used. Evaluation of cerebrospinal fluid (CSF) taken from a spinal tap may be normal, although sometimes the protein content of CSF is mildly increased.


A DNA test is available through the Orthopedic Foundation for Animals to look for the genetic mutation associated with this disease. The test identifies whether the dog is clear of the mutation, a carrier, or at risk for developing degenerative myelopathy. Unfortunately, definitive diagnosis can be made only by evaluating the spinal cord after death via an autopsy.



TREATMENT AND FOLLOW-UP




image Treatment Options


Currently, no proven effective treatment exists for degenerative myelopathy. Treatment consists of nursing care and assisting movement in dogs that cannot walk well. Carts, similar to wheelchairs, are sometimes used to help weak or paralyzed dogs move around.



image Follow-up Care


Animals are rechecked periodically to monitor the progression of disease. Urinary retention may predispose the dog to bladder infections, so periodic urinalyses may be recommended.



Prognosis


Long-term prognosis is very poor, because the disease progresses to paralysis over the course of 6 months to several years. Animals are usually euthanized when they become severely debilitated.



SPECIAL INSTRUCTIONS:



Discospondylitis


A. Courtenay Freeman, DVM


Marc Kent, DVM, DACVIM (Small Animal and Neurology)


Scott J. Schatzberg, DVM, PhD, DACVIM (Neurology)



BASIC INFORMATION



Description


Discospondylitis is an infection of the vertebrae and intervertebral disc spaces. The spine is made up of small bones called vertebrae that surround and protect the spinal cord. Between adjacent vertebrae there are discs (intervertebral discs) that act as cushions and provide strength and stability to the spine.


Discospondylitis occurs more commonly in young to middle-aged dogs and in medium to giant breeds, such as the Great Dane and the German shepherd dog. Male dogs are more commonly affected than females.



Causes


Infection occurs when a bacteria or fungus spreads to the disc space through the bloodstream from some other area in the body, such as the urinary tract, skin, heart valves, or mouth.


Staphylococcus species (Staph bacteria) are commonly responsible. Brucellosis causes the infection in a small percentage of dogs, especially breeding dogs. Brucellosis is also contagious to humans.



image Clinical Signs


Affected dogs are often systemically ill and may have neurologic abnormalities. Signs of systemic illness include fever, decreased appetite, lethargy, weight loss, and depression. Other signs may be present, depending on the source of the infection.


Pain in the area of the spine may be the only clinical sign noted in some dogs. Neurologic signs vary with the degree and location of spinal cord compression or instability and may include weakness, uncoordinated gait, and paralysis.



image Diagnostic Tests


A presumptive diagnosis is often made based on characteristic findings on x-rays of the spine. Routine laboratory tests (blood and urine) are usually performed to look for evidence of infection and to evaluate the dog’s general health. Brucellosis testing is usually recommended. Bacterial cultures of urine, blood, or any other infected tissue may be done to try and isolate the organism responsible for the infection. X-rays of the chest, an abdominal ultrasound, and/or an echocardiogram (heart ultrasound) may be recommended to look for an underlying source of the infection.


Computed tomography (CT scan) and magnetic resonance imaging (MRI) may provide information that is not visible on plain x-rays and may help determine whether surgery is indicated. In some instances, a needle is passed into the infected intervertebral disc space during a CT scan for the purpose of obtaining material for bacterial culture.



TREATMENT AND FOLLOW-UP




image Treatment Options


Treatment involves administration of antibiotics and pain medication, as well as cage rest:


• The infection is often treated with antibiotics for a minimum of 8 weeks. When possible, antibiotic therapy is based on bacterial culture results. If bacteria cannot be identified, then antibiotics are chosen that are effective against multiple types of bacteria.

• Because discospondylitis can be painful, pain medications are often used.

• Strict confinement is important during recovery, because infection of the intervertebral disc can cause spinal instability. Confinement involves cage rest, restriction of exercise, and leash walking only for urination and defecation.

• Improvement of signs associated with systemic illness (fever, lethargy) and pain is typically seen within the first week of treatment. If no improvement occurs, additional testing or treatment may be necessary.

Animals occasionally require surgery to remove material causing spinal cord compression and to stabilize the vertebral column. Surgery is usually done for animals with severe neurologic problems or pain that does respond to treatment.


Dogs that are positive for brucellosis present a dilemma with regard to treatment, because they may be contagious to other dogs and people. Contact your physician if there is a risk of human infection. (See the handouts on Brucellosis and Infertility in Male Dogs.)



image Follow-up Care


X-rays may be recommended every 6-8 weeks to look for resolution of the infection. Laboratory and other tests may also be repeated, depending on the original source or location of the infection. Often x-rays show little change for months. Antibiotics are typically continued for a minimum of 8 weeks regardless of x-ray findings, and some affected animals require several months of antibiotic therapy.



Prognosis


Prognosis is good in animals that respond to treatment within the first week. Animals with mild neurologic signs also have a favorable prognosis. Bacterial infections usually respond better than fungal infections to treatment. Bacterial infections that are resistant to treatment, fungal infections, and the presence of brucellosis are associated with a worse prognosis. Animals with severe neurologic signs or spinal instability have a poor prognosis for full recovery; however, aggressive antibiotic therapy and surgery may allow a complete recovery even in animals with severe disease.



SPECIAL INSTRUCTIONS:



Fibrocartilaginous Embolic Myelopathy


A. Courtenay Freeman, DVM


Marc Kent, DVM, DACVIM (Small Animal and Neurology)


Simon R. Platt, BVM&S, MRCVS, DACVIM (Neurology), DECVN



BASIC INFORMATION



Description


The spinal cord needs a proper blood supply to maintain normal function. Any decrease in blood (ischemia) or loss of blood supply (infarction) to a region of the spinal cord causes spinal cord damage and neurologic abnormalities. Blood supply is usually lost when an obstruction (embolus) develops within a blood vessel supplying the spinal cord.


Between adjacent vertebrae are discs (intervertebral discs) composed of a fibrous outer portion (annulus fibrosis) and a gel-like center (nucleus pulposus). These discs act as cushions between vertebrae and provide strength and stability to the spine. Fibrocartilaginous embolic myelopathy (FCEM) occurs when microscopic pieces of an intervertebral disc lodge in the blood vessels that supply blood to the spinal cord. The end result is spinal cord ischemia or infarction.



Causes


The cause of FCEM is unknown. Medium- to large-breed dogs are more commonly affected; however, smaller dogs, such as the miniature schnauzer, Shetland sheepdog, and Yorkshire terrier, can also develop FECM. Rarely, FECM may occur in cats.



image Clinical Signs


FCEM causes a sudden onset of neurologic abnormalities, which are dependent on the area of spinal cord affected. The condition is not typically painful; however, some animals cry out when the infarction occurs. Neurologic abnormalities do not usually progress or deteriorate from their initial severity and are usually worse on one side of the body or in one leg.


An uncoordinated gait suddenly develops that may involve all four legs, the legs on just one side of the body, or only the hind legs. The animals may be weak, scuff their feet, and cross their legs when walking. Severe injury to the spinal cord can result in paralysis and the inability to feel a painful stimulus applied to the toes.



image Diagnostic Tests


FCEM is initially suspected in animals based on the history and neurologic examination findings. Routine laboratory tests and x-rays may be recommended to rule out other conditions that produce similar signs, but they are usually normal. Magnetic resonance imaging (MRI) is the best test available to diagnose FCEM and to rule out other conditions. Others tests, such as myelography (a series of x-rays taken after injecting a dye around the spinal cord) or computed tomography (CT scan), can be used to eliminate other conditions but are often normal in cases of FCEM. A spinal tap and evaluation of cerebrospinal fluid (CSF) may be recommended to help eliminate other neurologic diseases.



TREATMENT AND FOLLOW-UP




image Treatment Options


No specific treatment exists for the spinal cord damage that develops during FCEM. Treatment involves supportive care and allowing time for the spinal cord to heal. Hospitalization is often required. Physical therapy, such as hydrotherapy, may be recommended during recovery. Supportive care is particularly important for paralyzed animals. These patients may develop urinary retention and bladder infections, urine-induced scalding of their skin, skin ulcers, and pneumonia if excellent nursing care is not provided.



image Follow-up Care


While the animal is hospitalized, neurologic functions are re-evaluated frequently. If the animal improves enough to be discharged, then periodic rechecks are usually done to evaluate signs of recovery. If the animal recovers the ability to walk and urinate on its own within the first 3 months, then long-term follow-up may not be necessary. If the animal does not regain the ability to walk or remains incontinent, frequent rechecks are necessary.



Prognosis


Prognosis depends on the severity of clinical signs. Many mild to moderately affected dogs improve over time. Recovery may take weeks to months, and some dogs do not return completely to normal. Residual neurologic problems can include inability to walk, weakness, and urinary or fecal incontinence. Any clinical signs remaining after 3-4 months are likely to be permanent. Prognosis is worse in animals that have severe spinal cord injury and do not (from the onset of FCEM) have the ability to feel a painful stimulus in the affected legs.



SPECIAL INSTRUCTIONS:



Granulomatous Meningoencephalitis and Necrotizing Encephalitis


A. Courtenay Freeman, DVM


Marc Kent, DVM, DACVIM (Small Animal and Neurology)


Scott J. Schatzberg, DVM, PhD, DACVIM (Neurology)



BASIC INFORMATION



Description


Granulomatous meningoencephalitis (GME) and necrotizing encephalitis (NE) are disorders that arise from inflammation of the brain and/or spinal cord and their coverings (the meninges). These diseases affect predominantly young, small-breed dogs.



Causes


Both GME and NE are presently considered to be autoimmune disorders, meaning that the body launches an abnormal attack against its own nervous system tissues. Potential triggers for the autoimmune attack may include infections and vaccinations. Genetics may also play a role in the development of GME and NE.


Although any breed of dog may be affected with GME, toy breeds are affected most often. Breeds commonly affected by NE include the pug, Maltese, Yorkshire terrier, Chihuahua, French bulldog, shih tzu, and Pomeranian.



image Clinical Signs


Clinical signs are variable and relate to the area of the brain or spinal cord that is inflamed. Clinical signs often worsen rapidly and may include seizures, lethargy, circling, loss of balance, and decreased vision. Both GME and NE can be fatal, with or without aggressive therapy.

Related posts:

  1. 16: Behavioral Disorders
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  3. 2: Cardiovascular System
  4. 15: Infectious Diseases

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Sep 11, 2016 | Posted by in SMALL ANIMAL | Comments Off on 4: Neurologic System

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