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Congenital and Inherited Spinal Cord Disorders

By Rebecca A. Packer, MS, DVM, DACVIM (Neurology), Neurology/Neurosurgery, Department of Veterinary Clinical Sciences, and Department of Basic Medical Sciences, School of Veterinary Medicine, Purdue University

Large Animals

Spinal muscular atrophy is an inherited disorder of Brown Swiss calves. The first clinical sign of spinal muscular atrophy is weakness of the pelvic limbs at 2–6 wk of age; calves (most are female) have difficulty getting up and then become recumbent. The characteristic sign is severe muscle atrophy, especially of the pelvic limbs. Histopathologic examination reveals degeneration and loss of motor neurons in the ventral horns of the spinal cord. Neurogenic atrophy of muscles is a consistent lesion. A similar disorder is seen in red Danish calves of American Brown Swiss lines. It is possible that spinal muscular atrophy and bovine progressive degenerative myeloencephalopathy (BPDME) are in some way related because they can be seen in the same blood lines, but the onset of BDPME occurs after 5 mo of age, and it causes ataxia and dysmetria rather than weakness and muscle atrophy. A motor neuron disease with neurofilament accumulation is seen in horned Hereford cattle in Canada with signs appearing soon after birth that are characterized by general tremors, incoordination, difficulty standing, and hyperesthesia to tactile stimulation. A suspected hereditary lower motor neuron disease with accumulation of neurofilaments also is seen in Yorkshire pigs around 5 wk of age, characterized by pelvic limb paresis progressing to recumbency. There is degeneration and loss of motor neurons throughout the spinal cord and brain stem. A similar condition is seen in young Hampshire pigs.

Bovine progressive degenerative myeloencephalopathy (BPDME, weaver syndrome) is a neurodegenerative disorder of Brown Swiss cattle that is seen in the USA, Canada, and Europe. Four basic criteria are required to establish a clinical diagnosis: 1) onset of bilateral pelvic limb ataxia and dysmetria at 5–8 mo of age; 2) deficient proprioceptive responses, ataxia in all four limbs, and progressive paraparesis; 3) normal spinal reflexes and cranial nerve function and absence of dramatic muscle atrophy; and 4) a familial relationship. The disease was initially described as “weaver” because of the peculiar weaving gait. The histopathologic changes are primarily in the sensory nervous system, in contrast to those of spinal muscular atrophy (see above). Spinal dysmyelination causes congenital lateral recumbency and opisthotonos, but spinal reflexes and alertness are normal.

Simmental encephalomyelopathy, which is seen in association with behavioral change (eg, aggression or dullness), has an onset in Simmental and Simmental-cross calves at 5–12 mo of age. The gait abnormality progresses from pelvic limb ataxia to recumbency with opisthotonos, and death occurs within 6 mo. It has been reported in the USA, UK, Australia, and New Zealand. Characteristic lesions consist of symmetric necrosis in the caudate nuclei and in other areas of the brain and spinal cord. Similar multifocal lesions are seen in 1- to 4-mo-old Limousin and Limousin-cross calves (with additional signs of blindness) in Australia and England and in Angus calves in Australia and the USA.

Progressive myelopathy of Murray Grey cattle in Australia is inherited (autosomal recessive), and calves usually show spastic paraparesis and ataxia at birth. Neuronal degeneration is widespread in the brain and spinal cord; primary demyelination also develops in the cord.

Progressive ataxia of Charolais cattle has been reported in the UK and North America. It causes clinical signs that are first noticed between 6 and 36 mo of age and progress throughout 1–2 yr from slight ataxia involving all four limbs to recumbency. Female cattle typically manifest a rhythmic pulsatile pattern of urination. Histologic lesions consist of eosinophilic plaques and myelin breakdown in the white matter of the cerebellum and spinal cord.

Neuraxonal dystrophy (NAD) appears to be inherited in sheep and causes an unsteady, stiff, and swaying gait that progresses to paraparesis and finally tetraparesis. Suffolk and New Zealand Coopworth sheep are affected as lambs 1–6 mo old; Romney sheep are affected at 6–18 mo of age. Merinos develop a very similar disease at 1–4 yr of age. NAD has also been seen in 4- to 7-mo-old Merino lambs. Axonal swellings (spheroids) are typically found in gray matter of brain stem and spinal cord, although in the older Merino sheep, axonal spheroids mainly develop in large white matter tracts of the CNS. NAD of Morgan horses affecting the lateral (accessory) cuneate nucleus usually develops at 6–12 mo of age and causes spastic paraparesis and pelvic limb ataxia. It is presumed to be inherited. NAD affecting several brain-stem nuclei and causing mild pelvic limb ataxia has also been reported in 4-mo-old Hafflinger horses in Germany.

Equine degenerative encephalomyelopathy has been mainly associated with vitamin E deficiency, but it may have a familial basis in Appaloosa horses and other breeds, based on occurrence of clusters of cases. Degeneration of the spinocerebellar tracts results in a slowly progressive, symmetric ataxia and paresis of all four limbs that starts as early as 7 mo of age. (Also see Degenerative Diseases of the Spinal Column and Cord.)

Progressive paresis in Angora goats has been reported in Australia and may have a heritable basis. Clinical signs of spastic paresis and ataxia appear from birth to 4 mo of age and progress to recumbency within a few weeks. Widespread (multisystem) neuronal degeneration is seen at necropsy.

Generalized glycogenosis in Shorthorn (type II) and Brahman (type IIb) cattle and in Corriedale sheep (resembling type II) is a lysosomal storage disease that causes ill thrift, respiratory signs, paraparesis, ataxia, and muscle weakness at 3–9 mo of age.

Cervical stenotic myelopathy (wobbler syndrome) is a compressive cervical spinal cord syndrome caused by vertebral canal stenosis, articular process osteophyte proliferation, and vertebral body tipping that occurs in young, rapidly growing horses. Thoroughbreds, Tennessee Walking Horses, and Warmbloods appear to be predisposed, with males being more commonly affected than females. Overnutrition is an important contributory factor, and the clinical signs often can be reversed in horses <9 mo old by reducing caloric intake and restricting exercise. Clinical signs typically become apparent from <6 mo up to 4 yr of age and include cervical myelopathy, with the pelvic limbs usually affected more severely. Imaging (eg, survey radiography, myelography, CT, MRI) can be used to identify stenotic or proliferative lesions, causing spinal cord compression in the midcervical spine. Treatment usually requires surgical decompression of the spinal cord and, in some cases, vertebral stabilization. Interbody fusion with titanium baskets (“Seattle Slew” implants) has shown more success; however, the prognosis remains guarded. In one study, 77% of horses showed neurologic improvement, with 46% regaining athletic function. Early treatment appears to be associated with improved surgical outcome.

Occipitoatlantoaxial malformation is an inherited disorder (autosomal recessive) in Arabian foals and may also be seen in Miniature horse foals, Holstein calves, and lambs. Clinical signs are progressive ataxia, tetraparesis, and an extended neck posture. Affected foals are usually tetraparetic at birth, although neurologic deficits may not develop for several years. Diagnosis is by radiography. Laminectomy has been reported to be successful in some cases.

Spina bifida is seen in most species and usually results in dysfunction of the tail and anus, incontinence, and sometimes pelvic limb weakness (see Small Animals).

Small Animals

Spinal muscular atrophy is an inherited lower motor neuron (LMN) disorder in Brittany Spaniels that can have an early (by 1 mo), intermediate (by 4–6 mo), or delayed (>1 yr old) onset. Rottweilers can also develop an early form of spinal muscular atrophy that is referred to as a motor neuron disease. Swedish Lapland puppies are affected at 5–7 wk of age, Stockard paralysis (seen in Great Danes crossed with Bloodhounds or Saint Bernards) has an onset at 11–14 wk, and English Pointers are affected when ~5 mo old. LMN disease also is seen in puppies of other breeds, including Doberman Pinschers and Briquet Griffon Vendéens; a focal form involving the thoracic limb(s) is seen in German Shepherds. Paraparesis or tetraparesis with neurogenic muscle atrophy are the main clinical features. The severe, generalized LMN disease in spinal muscular atrophy closely resembles the signs of a peripheral neuropathy. Loss of motor neurons in the spinal cord is the most striking feature on necropsy. There is no treatment.

Demyelination of Miniature Poodles is presumed to be an inherited disorder involving primarily the spinal cord. This rare condition causes paraparesis at 2–4 mo of age that rapidly progresses to tetraplegia. There is no treatment.

Ataxia of Parson Russell and Smooth-haired Fox Terriers can be confusing, because several forms of disease exist. In general, the diseases affecting these breeds are a spinocerebellar ataxia. The predominant clinical signs are cerebellar (cerebellar ataxia, intention tremor, hypermetria), but histopathologically at necropsy, spinal cord demyelination can be seen. Clinical signs begin to appear at ~2–6 mo of age. In one form of the disease, seizures and myokymia (in which the muscles appear to show verminous movement) can occur. The disease is progressive, although in some cases signs may stabilize but not regress, and some affected animals are able to live a relatively normal life, despite the abnormal movements.

Afghan Hound myelopathy is an inherited disorder that causes both demyelination and necrosis of the spinal cord. Paraparesis develops some time during the first year of life and progresses to paraplegia within 1 wk. The thoracic limbs become involved over the next 1–2 wk. A similar condition is seen in young Kooiker dogs (Dutch Decoy dogs) of either sex, with signs beginning at 3–12 mo of age. Prognosis is poor in both breeds.

Neuraxonal dystrophy is described in both cats and dogs but primarily in Rottweiler dogs (autosomal recessive inheritance). In Rottweilers, onset is between 3–24 mo of age, and the disorder progresses slowly over several years. Signs include cerebellar dysfunction and dysmetria in all four limbs, but with preservation of paw position sense, which should distinguish it from leukoencephalomyelopathy (see Small Animals) and from advanced motor neuron disease in the same breed. Collie dogs in Australia and New Zealand develop similar clinical signs at 2–4 mo of age. There is also early onset in Papillons and Chihuahuas and in cats (autosomal recessive in domestic tricolored cats). Axonal spheroids, often in specific regions of the brain and spinal cord, are the characteristic pathologic finding of these conditions.

Leukoencephalomyelopathy of Rottweilers has a later onset than neuraxonal dystrophy (see Small Animals), usually at ~2–3 yr of age. It is possible that the disorders have a similar basis, because animals occasionally may show histopathologic features of both conditions. In leukoencephalomyelopathy, there is no head tremor, and paw position sense is delayed. Bilaterally symmetric areas of spinal cord demyelination are the predominant findings on necropsy.

Calcium phosphate deposition in Great Danes causes mineralization of soft tissues and bone deformity, with dorsal displacement of C7. The resultant compressive myelopathy is seen in puppies 1–2 mo old. This condition is distinct from caudal cervical spondylomyelopathy (see below).

Degenerative myelopathy is a painless, slowly progressive myelopathy that occurs commonly in dogs. Clinical signs are typically consistent with a thoracolumbar spinal cord localization with pelvic limb paresis and ataxia, although progression may eventually involve the thoracic limbs. Histopathologic changes include a noninflammatory axonopathy and myelinopathy. German Shepherds, Pembroke Welsh Corgis, Boxers, Rhodesian Ridgebacks, and Chesapeake Bay Retrievers are predisposed. There is no treatment. Physical therapy slows the progression of clinical signs. A mutation has been identified that is associated with increased risk of developing degenerative myelopathy, and a genetic test is available to identify those dogs at higher risk of developing the disease.

Progressive axonopathy of Boxer dogs is an autosomal recessive disorder that causes patellar hyporeflexia, severe dysmetria, loss of paw position sense, and spastic paresis at 1–7 mo of age. Axonal spheroids are widespread in both the central and peripheral nervous system on necropsy. Although this condition causes loss of the patellar reflex, in general, the signs are more suggestive of spinal cord disease than of a peripheral neuropathy. There is no treatment, but affected dogs can live relatively comfortably for a considerable time.

Breed-associated aseptic meningitis (steroid-responsive meningitis-arteritis) has been reported in Beagles, Bernese Mountain Dogs, Boxers, German Short-haired Pointers, and sporadically in other breeds. The main signs are neck pain, pyrexia, and dramatic pleocytosis in the CSF in young dogs. Prognosis is guarded to favorable, especially in dogs with acute disease that are treated promptly using immunosuppressive doses of corticosteroids.

Congenital vertebral malformations include hemivertebrae (shortened or misshapen vertebrae), block (fused) vertebrae, and butterfly vertebrae (having a sagittal cleft). Hemivertebrae are most common in screw-tailed dog breeds and are inherited in German Shorthaired Pointers. Decompressive surgery can be very successful but sometimes needs to be combined with spinal stabilization. Multiple cartilaginous exostosis is a benign proliferation of cartilage or bone that can affect the ribs, long bones, or vertebrae and may have a familial basis. Transitional vertebrae are often clinically associated with lumbosacral stenosis. Myelography or specialized imaging techniques (eg, CT, MRI) are usually required to confirm spinal cord compression in these congenital conditions. Treatment consists of surgical removal.

Caudal cervical spondylomyelopathy (wobbler syndrome) may have a heritable basis in Borzois (5–8 yr) and Basset Hounds (<8 mo) and probably also Doberman Pinschers (≥2 yr) and Great Danes (<2 yr). Neurologic deficits range from mild ataxia of the pelvic limbs to tetraplegia. Affected dogs often keep their neck flexed ventrally, and there may be caudal cervical pain. Spinal radiographs may show malalignment or remodeling of the vertebrae, narrowing of one or more disk spaces, or spondylosis deformans. CT/myelography or MRI usually reveals a marked stenosis at the cranial orifice of the midcervical or caudal cervical vertebrae. Several surgical techniques can provide stabilization of the vertebrae or decompression of the spinal cord.

Atlantoaxial subluxation is most commonly seen as a congenital disorder in young toy or miniature breeds of dogs and occasionally as a congenital disorder in several large breeds, including Rottweilers and Doberman Pinschers. Signs usually develop within the first few years of life and consist of an acute or slowly progressive onset of neck pain or gait dysfunction, ranging from ataxia to tetraplegia. Radiographic confirmation of diagnosis should be followed by stabilization using ventral fixation. The prognosis is guarded.

Arachnoid diverticuli (arachnoid cysts, arachnoid pseudocysts, meningeal cysts, leptomeningeal cysts, subarachnoid cysts) cause accumulations of CSF and a focal myelopathy in young dogs. The cause is unknown, but some cysts may have a congenital origin. Signs consist of progressive ataxia and weakness. Diagnosis is made by myelography and/or MRI. Prognosis may be favorable after surgical excision, although recurrence is possible.

Spinal dysraphism or myelodysplasia includes anomalies of the skin, vertebrae, and spinal cord that are secondary to faulty closure of the neural tube. Spinal dysraphism is inherited in Weimaraners. Neurologic deficits are evident by 4–6 wk of age and include paraparesis and a symmetric “bunny-hopping” gait in the pelvic limbs. There is a bilateral flexor reflex; pinching one paw elicits flexion of both pelvic limbs. There may be scoliosis or abnormal hair streams on the dorsal aspect of the neck. Diagnosis is based on clinical signs and imaging techniques such as myelography or MRI. There is no treatment, but neurologic deficits usually do not progress. Similar malformations have been seen in other breeds of dogs and in calves, foals, and lambs.

Syringomyelia is the development of one or more fluid-filled cavities within the spinal cord. Hydromyelia is accumulation of fluid within an enlarged central canal of the spinal cord. It is often difficult to differentiate between syringomyelia and hydromyelia, so the term syringohydromyelia is often used. Syringohydromyelia causes progressive ataxia and paresis; scoliosis and spinal pain is possible. Causes include trauma, neoplasia, inflammatory conditions, and developmental malformations. The most common cause in dogs is caudal occipital malformation syndrome (see Small Animals).

Spina bifida occulta is a failure of the neural arch to fuse; if the spinal cord is also involved, it is called spina bifida manifesta. The most likely clinical signs of spina bifida are LMN signs in the pelvic limbs and urinary or fecal incontinence. The prognosis for animals with substantial neurologic deficits is poor. Spina bifida can also accompany the sacrocaudal dysgenesis that is inherited as an autosomal dominant trait in Manx cats.

Pilonidal sinus (dermoid sinus, dermoid cyst) is another consequence of faulty neural tubulation that appears to be inherited (autosomal recessive) in Rhodesian Ridgeback dogs. The sinus is lined by skin and may communicate with the subarachnoid space, causing possible meningitis or myelitis. Treatment consists of antibiotics and surgical excision of the sinus.

Epidermoid cysts are rare lesions that arise from entrapment of epithelial cells during closure of the neural tube. Myelography or MRI will reveal an intramedullary lesion in a young dog with progressive neurologic deficits.

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