19. Nervous System Disorders

CHAPTER 19. Nervous System Disorders

Patricia A. Schenck




DIAGNOSTIC APPROACH






I. Principles of neurologic examination




A. Determine whether neurologic disease is present, and localize the lesion


B. Perform examination in a consistent manner




1. Start with a general examination and progress to a specific examination


2. Do painful parts of the examination last


II. Procedures for the neurologic examination




A. General observations




1. Mental status is regulated by the brainstem and cerebrum




a. Evaluate level of consciousness (alert, depressed, stuporous, comatose)


b. Evaluate behavior (appropriate, demented). Dementia reflects a cerebral disorder


2. Head posture is reflective of the vestibular system. A head tilt suggests a vestibular injury


3. Coordination of head movement is regulated by the cerebellum


4. Circling is usually toward the diseased side. Any brain lesion can cause circling


B. Gait and stance




1. A normal gait requires integration of the entire nervous system




a. Ataxia is rarely caused by cerebral or peripheral nerve lesions


b. Cerebellar lesions typically cause ataxia


c. Cerebral lesions may produce mild weakness


d. More pronounced weakness is caused by injury to the brainstem, spinal cord, or peripheral spinal nerves


2. An abnormal stance may be caused by decreased proprioception, weakness, or pain


C. Tests of postural reactions




1. General findings




a. Cerebral lesions: Postural deficit is on the opposite side of the body (contralateral)


b. Brainstem lesions: Postural deficits are bilateral, but worse on the same side as the lesion (ipsilateral)


c. Cerebellar, spinal cord, peripheral nerve lesions: Postural deficits are ipsilateral


d. Vestibular lesions: Postural reactions are preserved, but the animal leans or falls toward the diseased side


2. Proprioceptive positioning: Turn paw so animal bears weight on dorsal surface. The animal should quickly flip the paw over to the normal position


3. Hemihopping: Hold limbs on one side off the ground and hop the animal sideways on the other two limbs. If conscious proprioception (CP) is intact and there is adequate strength in the limbs, a normal hopping response is quickly initiated


4. Wheelbarrowing: Hold either front or hind legs off the ground and walk the animal forwards and backwards. A normal animal can walk easily


D. Cranial nerve examination




1. Menace response: Make a menacing gesture toward the animal; a normal animal should try to avoid the gesture. Tests both cranial nerves (CN) 2 and CN7.


2. Pupillary light reflex: Illuminate the eye with a bright light; both pupils should constrict. Tests both CN2 and CN3. Lesions of CN2 cause loss of constriction in both pupils when the affected eye is examined. Lesions of CN3 cause loss of constriction in the affected eye, with constriction in the unaffected eye, regardless of which eye is illuminated


3. Pupillary symmetry evaluates CN3 and the sympathetic nerve to the eye. If CN3 is abnormal, the large pupil is denervated, and the papillary light reflex (PLR) is absent. If the sympathetic nerve is damaged, the smaller pupil is abnormal, but the PLR is normal in both eyes


4. Pupillary size reflects the integrity of CN3 and sympathetic nerve. Large pupils can be due to CN3 paralysis. Small pupils may be due to loss of sympathetic tone


5. Ocular position is determined by CN3, CN4, CN6, and CN8




a. Injury to CN6 causes medial strabismus


b. Injury to CN3 or CN8 causes ventrolateral strabismus



7. Facial symmetry assesses CN7; abnormalities suggest a cerebral lesion if contralateral, and brainstem or peripheral nerve lesions if ipsilateral


8. Palpebral reflex assesses CN5 and CN7. Touch the palpebral margins to produce a blink normally


9. Corneal reflex tests CN5 and CN7. Touching the cornea should produce a normal blink


10. Retractor oculi reflex tests CN5 and CN6. Touching the cornea should produce a retraction of the eye into the orbit normally


11. Facial sensory examination tests CN5. Stimulation of the nasal mucosa should result in an avoidance response


12. Gag reflex tests CN9, CN10, and brainstem. Lack of a swallowing reflex indicates either a brainstem injury or CN injury


13. Tongue atrophy indicates either a brainstem or CN12 lesion. Deviation of the tongue can be caused by cerebral injuries


E. Spinal reflex examination




1. Proprioceptive reflexes. A standard grading of the reflex is useful




a. Triceps reflex evaluates the radial nerve from C7 to T2. Normally there should be a slight extension of the elbow


b. Extensor carpi radialis reflex also evaluates C7 to T2. Normally the carpus extends


c. Biceps reflex evaluates the musculocutaneous nerve (from C6 to C7)


d. Patellar reflex tests femoral nerve and L4 to L6. An exaggerated response suggests an upper motor neuron (UMN) lesion


e. Cranial tibialis reflex tests the peroneal branch of the sciatic nerve from L6 to S2


2. Nociceptive spinal reflexes are initiated by a painful stimulus. Loss of the reflex suggests a lower motor neuron (LMN) lesion




a. Thoracic limb flexor reflex tests spinal cord segments C6 to T2


b. Pelvic limb flexor reflex tests segments L6 to S2


c. Perineal reflex tests S1 to S3


3. Special reflexes




a. Babinski reflex is in the hindlimbs. Stroking the plantar aspect of the metatarsus should cause slight flexion of the toes, or no response. A positive Babinski reflex signifies UMN disease, and the toes spread apart and elevate


b. Crossed extensor reflex. With UMN disease, the stimulated limb flexes and the contralateral limb extends


F. Nociceptive evaluation




1. Decreased pain perception can be the result of peripheral nerve, spinal cord, brainstem, or cerebral lesion


2. Increased sensitivity or exaggerated response to pain. A nonpainful stimulus is applied down the spine, looking for an area of acute response to the stimulus


III. Interpretation of the neurologic examination




A. Central nervous system (CNS) vs. peripheral nerve disease




1. If there are proprioceptive deficits, then lesion is most likely within the CNS


2. If there are UMN signs, there is usually a CNS lesion


3. If seizures or altered consciousness is present, a CNS lesion is usually the cause


4. If there are CN deficits and limb signs, the lesion is in the CNS


5. If there are CN deficits with no other signs, the lesion is most likely in the peripheral nervous portion of the CN


6. If there is diffuse weakness, diminished reflexes, without postural deficits, the lesion is usually in the peripheral nervous system


B. Location of lesion




1. If clinical signs are only in the limbs, the lesion is most likely below the foramen magnum


2. If there are CN deficits, seizures, altered consciousness, or abnormal head posture, the lesion is most likely above the foramen magnum


IV. Diagnostic testing: general




A. Hematology: Usually minimal changes


B. Biochemical tests: Alterations in blood glucose, calcium, potassium, and sodium can impact nervous system function. In addition, acid-base status, uremia, hyperlipidemia, hyperammonemia, and hyperviscosity can cause neurologic signs


C. Urinalysis: Metabolic diseases that impact the nervous system—such as diabetes, renal disease, and liver disease—can produce changes in the urine


D. Ophthalmologic examination is warranted if there is inflammatory disease


E. Blood pressure measurement is warranted as hypertension can predispose to CNS vascular disease


F. Thoracic radiographs and abdominal ultrasound are useful if inflammatory or neoplastic disease is suspected


G. Fecal analysis: Parasites can cause CNS disease in young animals


H. Serology for viral or rickettsial diseases may be indicated


I. Immunofluorescence can be used to identify some viral diseases


J. Toxicology may be utilized to identify certain toxins



VI. Cerebrospinal fluid (CSF) collection and analysis




A. CSF analysis is indicated if inflammation is suspected


B. CSF analysis is contraindicated if intracranial pressure is elevated


C. CSF collection is performed under general anesthesia. If a brain disorder is suspected, collect CSF at the cerebellomedullary cistern. For spinal cord disorders, collect CSF at the lumbar space


D. CSF analysis




1. Gross examination




a. CSF should normally be clear and colorless


b. CSF is turbid in inflammation


c. Pink color indicates blood contamination; yellow-orange color indicates breakdown of hemoglobin from previous hemorrhage or severe elevation in CSF protein


2. Cytology




a. Suppurative meningitis is characterized by an increase in neutrophils and indicates bacterial encephalitis, meningioma, vasculitis in young dogs or feline infectious peritonitis (FIP) in cats


b. Mixed inflammation is characterized by an increase in a mixed population of cells and usually indicates fungal, protozoal, or idiopathic encephalitis. It may be seen in chronic bacterial infections


c. Nonsuppurative inflammation is indicative of immune-mediated encephalitis, rickettsial infection, and some viral infections


d. Eosinophilic inflammation is secondary to immune-mediated encephalitis, fungal or protozoal infections, and parasite migration


e. Increased red blood cells (RBCs) may be due to contamination during the CSF tap but can also be due to hemorrhage due to trauma. Erythrophagocytosis is an indication of previous hemorrhage


f. Other cells or organisms identified include tumor cells cryptococcal or fungal organisms, distemper inclusions, bacteria, or rickettsial organisms


3. Protein concentration is normally low in CSF. Disorders that increase CSF protein include encephalitis, meningitis, neoplasia, chronic neurodegenerative conditions, and trauma


4. CSF can be tested for antibodies against infectious agents


VII. Electroencephalography (EEG)




A. An EEG is useful with corticocerebral lesions. Sedation is usually required to minimize movement


B. The major disadvantage is that no information is gathered regarding cause


VIII. Brainstem auditory evoked response tests hearing


IX. Electrodiagnostic examination of the motor unit




A. Needle electromyography (EMG) gives information about motor unit innervation and muscle membrane ion conductance


B. Nerve conduction studies measure the action potential conduction velocity between points along a motor nerve


C. Repetitive nerve stimulation is useful in neuromuscular junction diseases


D. Tensilon or edrophonium chloride test. Intravenous (IV) administration transiently alleviates signs of myasthenia gravis


BRAIN AND CRANIAL NERVE DISORDERS






I. Clinical signs




A. Brainstem lesions




1. Cranial nerve dysfunction (CN3-CN12) is common


2. Clinical signs involving facial expression (CN7) and mastication (CN5) are common


3. Head tilt, circling, and falling are signs of vestibular nuclei damage


4. Ascending white matter tract injury causes ipsilateral conscious proprioceptive deficits


5. Descending UMN injury causes tetraparesis or paralysis


6. Severe brainstem lesions result in altered consciousness and can affect cardiovascular and respiratory regulation


B. Cerebellar lesions




1. Incoordination during voluntary movements


2. Truncal swaying and a wide-based stance


3. Intention tremor of the head


4. The menace response is absent ipsilaterally


5. Mild pupil dilation may be present ipsilaterally


6. Vestibular signs and opisthotonus may be present


7. Mental status is usually normal


C. Forebrain lesions




1. Seizures, personality changes, and dementia can occur with both diffuse and focal disorders


2. Diffuse disorders may cause conscious proprioceptive deficits, stupor, coma, absent response to pain, generalized ataxia, and bilateral miosis


3. Focal disorders may cause circling, contralateral conscious proprioceptive deficits, contralateral facial sensory deficits and weakness. Focal diencephalic lesions can cause lethargy, altered mentation, or circling. Head and neck pain can result from structural lesions



E. Herniation from space-occupying brain lesions




1. If there is transtentorial herniation, clinical signs include extensor rigidity in the limbs, and stupor or coma


2. If there is foramen magnum herniation, clinical signs include opisthotonus, thoracic limb rigidity, and severe alterations in respiration


II. Neoplasia usually affects middle-aged and older animals




A. Causes




1. The most common primary tumors in the dog are meningioma and glioma (astrocytoma, glioblastomas, oligodendrogliomas, ependymomas, and choroids plexus papillomas/carcinomas)




a. Meningiomas occur mostly in dolichocephalic breeds, and gliomas occur mostly in brachycephalic breeds


b. Meningiomas are often located in the olfactory or frontal lobe


2. The most common primary tumor in the feline is meningioma; frequently multiple


3. Secondary brain tumors occur from hematogenous spread or extension from surrounding tissues




a. Tumors with hematogenous spread are hemangiosarcoma, malignant melanoma, mammary adenocarcinoma, and pulmonary adenocarcinoma


b. In the dog, secondary lymphoma occurs with the multicentric form. Multicentric malignant histiocytosis can also invade the CNS


c. Tumors invading by extension are usually nasal adenocarcinoma, pituitary macroadenoma or carcinoma, and bony tumors of the skull


B. Clinical signs depend on the location and type of tumor




1. Signs may be vague, with irritability, changes in behavior, pacing, and lethargy


2. Signs may arise from obstruction of CSF flow or from herniation. Vestibular symptoms, or cranial nerve signs may also be seen


C. Diagnosis




1. Laboratory testing is used to rule out other causes of nervous system signs. Adrenal function testing may reveal the presence of pituitary macroadenoma


2. Ophthalmologic examination should be done to check for papilledema, which is a sign of increased intracranial pressure


3. EEG may detect brain lesions or epilepsy


4. Radiography may reveal some bony lesions or metastasis


5. CT and MRI are used for more precise definition of tumors


6. CSF analysis is useful to distinguish inflammation from neoplasia


D. Treatment




1. Corticosteroids are used to treat edema and meningioma


2. Mannitol is used in those with increased intracranial pressure. Furosemide will help prolong the effects of mannitol


3. Phenobarbital with or without potassium bromide is indicated if seizures are present


4. Lomustine may be beneficial in treating gliomas and meningiomas


5. Surgery may be possible, depending on location


6. Radiation therapy consistently prolongs survival, especially for meningiomas and canine pituitary tumors


III. Inflammatory brain diseases




A. Infectious meningoencephalitis (more common in cats)




1. Many agents cause inflammatory brain disease, including viral, fungal, rickettsial, and protozoal agents


2. Diagnostic testing includes complete blood cell count (CBC), chemistry profile, urinalysis, radiographs, and ophthalmological evaluation




a. CSF analysis may be beneficial; CSF titers can be determined


b. Cytologic evaluation of skin lesions, exudates, and aspirates may identify a pathogen


3. Treatment depends on the underlying cause




a. Usually requires prolonged therapy


b. Most effective if parenteral antibiotics are administered


B. Idiopathic inflammatory brain disorders (more common in dogs)





2. Necrotizing encephalitis




a. Similar to GME and may have an immune-mediated component. Multifocal, necrotic, cavitating lesions are commonly seen


b. Clinical signs include seizures, dementia, blindness, neck pain, and ataxia. Necrotizing encephalitis usually occurs in toy breed between 9 months and 5 years of age


c. Diagnosis is by exclusion of GME, infectious disease, and neoplasia. A marked mononuclear cell inflammation is seen in the CSF


d. Treat with prednisone and anticonvulsants. The prognosis is poor


3. Generalized idiopathic tremors (Little White Shaker syndrome)




a. Occurs in toy and small-breed dogs with white coat color; other breeds can be affected. Usually affects dogs younger than 6 years


b. Clinical signs include coarse body tremors that worsen with stress, exercise, or handling


c. Differential diagnosis includes neurotoxin exposure, seizures, and inflammatory brain diseases


d. Treatment is with diazepam and prednisone. The prognosis is good, although relapses may occur


IV. Vascular diseases




A. Vascular encephalopathies




1. Typically affects older animals. Ischemia or infarction occurs as a result of thrombosis of a blood vessel secondary to an underlying condition (e.g., hypertension, atherosclerosis, hyperviscosity, tumor emboli)


2. Clinical signs are usually asymmetrical and cause signs of forebrain disease or vestibular disease


3. Diagnosis is by diagnosing the underlying disorder; MRI is useful in determining the extent of the ischemia or hemorrhage


4. Treatment of the underlying condition is important; anticonvulsants or mannitol therapy to treat brain edema may be necessary


B. Feline ischemic encephalopathy




1. Occurs in young to middle-aged cats, with a higher incidence in late summer. It is caused by a cerebral infarction of the middle cerebral artery


2. Clinical signs are of cerebral dysfunction. Seizures may be the only sign; clinical signs may improve over months


3. Rule out other causes of vascular disease and cerebral disease; MRI may show cerebral edema


4. Anticonvulsant therapy may be needed; prednisone is not effective

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Apr 6, 2017 | Posted by in GENERAL | Comments Off on 19. Nervous System Disorders

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