Disorders of the Spinal Cord

Chapter 128 Disorders of the Spinal Cord



Patricia J. Luttgen, Paul A. Cuddon


The term spinal cord disorders (see Table 128-1 for classification and examples) broadly refers to all diseases affecting the spinal cord. Clinically, spinal cord disorders may cause dysfunction in one or more limbs. Urinary and fecal incontinence and tail dysfunction may also be seen.


Table 128-1 CLASSIFICATION AND EXAMPLES OF SPINAL CORD DISORDERS






















































































Category Examples
Degenerative Globoid cell leukodystrophy
Degenerative myelopathy of German shepherds
Hereditary spinal muscular atrophy of Brittany spaniels
Hereditary ataxia of smooth-haired and Jack Russell terriers
Caudal cervical spondylomyelopathy
Anomalous Spinal dysraphism
Spina bifida
Myelodysplasia
Atlantoaxial subluxation
Hemivertebrae
Spinal arachnoid cysts
Caudal occipital malformation syndrome with syringohydromyelia
Neoplastic Intramedullary ependymoma
Intramedullary astrocytoma
Intramedullary oligodendroglioma
Extramedullary intradural meningioma
Extramedullary peripheral nerve sheath tumor
Lymphoma
Extradural vertebral osteosarcoma
Infectious Feline infectious peritonitis
Canine distemper myelitis
Rabies
Cryptococcosis
Rickettsial diseases
Neosporosis
Toxoplasmosis
Discospondylitis
Immune-mediated Granulomatous meningoencephalitis
Steroid-responsive meningitis/vasculitis
Toxic Tetanus
Strychnine
Traumatic Intervertebral disc herniation
Fracture/luxation of spinal column
Vascular Fibrocartilaginous embolization
Progressive hemorrhagic myelomalacia
Caudal aortic embolization



Key Point


Disorders of the spinal cord do not cause signs referable to diseases above the foramen magnum, such as mentation changes, cranial nerve deficits, and vestibular ataxia.



ETIOLOGY


Spinal cord disorders can arise from numerous insults and may be associated with particular signalments (breed, age, sex) and neuroanatomic localizations. Many of these disorders cause relatively predictable patterns of onset (acute versus chronic) and clinical signs (progressive versus nonprogressive).



Anomalies


Anomalies of the spinal cord usually are first recognized when ambulation begins and are nonprogressive. Examples include spinal dysraphism in Weimaraners and sacrocaudal dysgenesis with spina bifida in English bulldogs and Manx cats.



• For some anomalies, traumatically induced “decompensation” may be required for minor lesions to be recognized clinically. An example is atlantoaxial subluxation of toy breeds in which ligamentous and dens malformations create C1-C2 instability and an increased risk of C1-C2 luxation.

• Some anomalies slowly worsen over the life of the animal to cause progressive worsening of signs. Dogs with congenital arachnoid cysts show slowly progressive spinal cord signs as the cavitating lesion expands in size. In dogs with caudal occipital malformation syndrome (COMS), progressive foramen magnum compression causes disruption of cerebrospinal fluid (CSF) flow and syringohydromyelia formation. Signs of slowly progressive spinal cord dysfunction can be seen at almost any age.

• Vertebral anomalies that compromise the stability of the vertebral column or the canal size may cause spinal cord dysfunction secondary to compression. For example, hemivertebra may lead to vertebral body luxation, and malarticulation/malformation of articular facets may lead to spinal canal stenosis.


Degenerative Disorders


Degenerative conditions are usually insidious in onset and chronically progressive.



• Many of these conditions are inherited and are seen in young animals. Examples include lysosomal storage disorders such as globoid cell leukodystrophy and Niemann-Pick disease, spinal muscular atrophy of Brittany spaniels, and hereditary ataxia of Jack Russell and smooth-haired fox terriers.

• Other neurodegenerative disorders are age-related and may be familial. Examples include degenerative myelopathy seen in older, large-breed dogs, particularly the German shepherd. In this disorder, white matter degeneration is most severe in the T3-L3 region.

• Some age-related degenerative disorders affect bony and soft tissues surrounding the spinal cord and result in spinal cord compression. Examples include cervical spondylomyelopathy in Doberman pinschers, intervertebral disc disease (discussed under spinal cord trauma below), lumbosacral spondylopathy/stenosis of German shepherd dogs, and mucopolysaccharidosis in cats.


Trauma



• Trauma can arise from external sources (e.g., being hit by a car or a bullet) or from internal sources (e.g., disc herniation or a pathologically collapsed vertebra).

• Clinical signs are usually acute and nonprogressive. However, progressive signs may be seen.

• Pathologic vertebral body fractures can occur secondary to vertebral body neoplasia or osteomyelitis.


Intervertebral Disc Disease



• Type I intervertebral disc disease is characterized by sudden disc extrusion. Signs of spinal cord compression are usually acute and may progress over a few hours or days.

• Type II intervertebral disc disease is characterized by slow protrusion of a slowly degenerating disc. Signs are usually gradual in onset and progression.


Inflammation/Infection


Numerous infectious agents can affect the spinal cord and surrounding structures of animals of all breeds and ages. Clinical signs vary depending on the inciting agent, the location of the lesion, and the degree of spinal cord involvement. Signs are usually rapid in onset and progression. Often inflammatory disease of the central nervous system (CNS) is not confined to the spinal cord, and clinical signs of brain involvement will also be present (see Chapter 126).



Bacterial



• Primary bacterial meningitis or meningomyelitis is infrequently diagnosed in dogs and cats. Bacterial infection is most commonly introduced secondary to infection of surrounding tissues or to trauma.
• For example, bacterial discospondylitis causes discomfort from disc and vertebral body infection and may cause neurologic deficits if secondary compression of the spinal cord occurs.


Viral


Viral myelitis is a relatively common problem in dogs and cats. Clinical presentation and neuroanatomic localization vary.



• Typically, encephalitic signs are associated with rabies infection, but this virus may also cause signs of myelitis (see Chapter 15).

• All ages of dogs are susceptible to canine distemper virus (CDV; see Chapter 13). Previous vaccination does not preclude “breaks” in immunocompetency due to other illnesses or disease states. Signs of spinal cord disorder without associated encephalitic signs may occur.

• In cats, coronavirus (feline infectious peritonitis) and retrovirus (feline leukemia virus and feline immunodeficiency virus) infections may cause signs of spinal cord dysfunction with or without signs of brain involvement (see Chapters 8, 9, and 10).


Fungal



• Fungal myelitis has been reported in patients with cryptococcosis, blastomycosis, histoplasmosis, and coccidioidomycosis.

• Multiple levels of the nervous system usually are involved simultaneously (e.g., eyes, brain, spinal cord); however, signs are limited to the spinal cord in some patients.

• Systemic mycoses are discussed in Chapter 20.


Rickettsial



• In addition to other clinical signs, tickborne rickettsial diseases such as ehrlichiosis and Rocky Mountain spotted fever may cause myelitis, meningitis, and encephalitis (see Chapter 17).


Protozoal



• Neospora caninum may cause pelvic limb rigidity followed by a rapid ascending tetraparesis/tetraplegia due to a severe myelitis (see Chapter 21).

• Toxoplasmosis can also cause spinal cord myelitis and radiculitis, especially in cats (see Chapter 21). Encephalitis, ocular involvement, and myositis may also be present.

• We recommend testing for both organisms if protozoal myelitis is suspected.


Granulomatous Meningoencephalomyelitis (GME)



• This is believed to be an immune-mediated disorder of the brain and spinal cord.

• Signs of spinal cord myelitis and meningitis may predominate. The cervical area seems to be the preferred site of involvement in the spinal cord.

• GME primarily affects the white matter of the CNS and consists of perivascular accumulations of lymphocytes, plasma cells, and reticuloendothelial cells. Perivascular cuffs can coalesce to produce granulomas.

• The disease is invariably progressive in nature (see Chapter 126).


Immune-Mediated Disorders



• Immune-mediated steroid-responsive meningitis and/or meningeal-vasculitis have been reported in young dogs of many breeds. Boxers are commonly affected with this disorder. A more severe form of this syndrome (necrotizing vasculitis) has been reported in beagles, Bernese Mountain dogs, and German short-haired pointers.

• Clinical signs are typical of spinal meningitis including neck stiffness, hyperesthesia, and fever.


Toxins



• Strychnine and tetanus directly affect the spinal cord in dogs and cats. These toxins act in a similar manner.

• Tetanus toxin decreases the release of the inhibitory neurotransmitters, γ-aminobutyric acid and glycine in the spinal cord, whereas strychnine competitively blocks the inhibitory effect of glycine.

• Clinical onset is usually acute, and the disease progresses to a state of severe tetany.


Vascular Disorders



• Vascular conditions resulting in ischemia of the spinal cord most often cause peracute to acute non-progressive spinal cord dysfunction. Intramedullary spinal cord lesions are nonpainful.

• The lesion may affect any area of the spinal cord.



Key Point


In adult large-breed dogs, fibrocartilaginous embolization is the most common cause of vascular injury to the spinal cord. Lesions are often asymmetrical and may affect several spinal cord segments in a continuous or discontinuous distribution.



• In cats, caudal aortic embolization secondary to cardiomyopathy is a common cause of spinal cord vascular injury.


Neoplasia



• Neoplasia of the spinal cord can affect animals of all ages and breeds. Initial clinical signs vary, depending on the type and location of the tumor. Signs usually are progressive over weeks to months. Two major types of tumors affect the spinal cord: intramedullary and extramedullary.
• Intramedullary tumors such as astrocytoma and ependymoma arise from the spinal cord itself, causing damage by derangement of the normal anatomy. Hemangiosarcoma, lymphoma, and other tumors may metastasize to intramedullary sites in the spinal cord.

• Extramedullary tumors arise from tissues surrounding the spinal cord and cause damage by compression. Extramedullary tumors can be located intradurally (e.g., meningiomas and nerve root tumors) or extradurally (e.g., vertebral osteosarcomas and multiple myeloma). Extradural lymphoma is a common cause of caudal paresis in cats.

• See Chapter 101 for discussion of neoplasia of the axial skeleton.


CLINICAL SIGNS


Characteristic clinical signs of spinal cord injury include spinal pain or hyperpathia, proprioceptive deficits, paresis or plegia, and nociceptive (pain) loss.



Hyperpathia



• Involvement of nerve roots, dura, and other extradural structures adjacent to the spinal cord will result in hyperpathia (exaggerated response to a painful stimulus).

• Spinal hyperpathia can be assessed by observing for pain on spinal palpation, neck guarding or stiffness, or signs of a root signature (holding/favoring the limb at rest).

• Extradural and extramedullary lesions are often painful. This can be helpful in lesion localization.


Postural Deficits and Ataxia (Proprioceptive Dysfunction)



• Ascending sensory tracts in cord white matter convey proprioceptive information from the limbs to the brain.

• Conscious proprioceptive (CP) tracts convey signals concerning limb position at rest to the cerebral cortex.

• Unconscious proprioception (UP) tracts convey signals concerning limb position during locomotion to the cerebellum.

• Injury to CP tracts causes knuckling and slow postural reactions (as during the hopping test).

• Injury to UP tracts causes ataxia (“drunken” gait with crossing over, wide-based posture, truncal sway, circumduction, and, occasionally, hypermetria). Ataxia is usually observed in the limbs caudal to the lesion.



Key Point


Ascending proprioceptive fibers in the spinal cord are the most sensitive to compressive lesions. Therefore, CP deficits and incoordination (sensory ataxia) of one or more limbs is commonly the initial sign of spinal cord disease.



Paresis and Plegia



• Descending upper motor neuron (UMN) tracts in cord white matter originate in brain and terminate in the spinal cord. The UMN system modulates functions of the thoracic and pelvic limb lower motor neurons (LMNs) located in the gray matter of cord segments C6-T2 and L4-S2, respectively.
• UMN inputs facilitate limb strength and motor abilities and inhibit some spinal reflexes and limb extensor muscle tone.

• LMNs also facilitate strength, relay locomotor signals from the UMN system, are part of the reflex arc for spinal reflexes, and provide trophic support to limb muscles.

• Injury to either UMN or LMN pathways will cause varying degrees of paresis (weakness) or plegia (weakness with loss of locomotor abilities) of the limbs.



Key Point


UMN injury results in paresis to limbs caudal to the level of the lesion, and LMN injury results in paresis to limbs at the level of the lesion.



• Injury to UMN pathways results in retention of spinal reflexes and increased extensor muscle tone when animals are recumbent.

Related posts:

  1. Feline Infectious Peritonitis (Feline Coronavirus)
  2. Borreliosis (Lyme Disease)
  3. Immune-Mediated Dermatoses
  4. Otitis Media and Otitis Interna

Stay updated, free articles. Join our Telegram channel
Tags:
Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Disorders of the Spinal Cord

Full access? Get Clinical Tree
Get Clinical Tree app for offline access