Congenital and Inherited Spinal Cord Disorders in Animals
Also see Diseases of the Spinal Column and Cord.
Spinal muscular atrophy is an autosomal recessive inherited disorder of Brown Swiss calves. A mutation in the FVT1 gene is suspected. The first clinical sign of spinal muscular atrophy is weakness of the pelvic limbs at 2–6 weeks 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 months of age, causes ataxia and dysmetria rather than weakness and muscle atrophy, and candidate genes appear different between these two diseases.
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 weeks 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 an autosomal recessive neurodegenerative disorder of Brown Swiss cattle that is seen in the USA, Canada, and Europe. It is most likely due to a mutation in the PNPL8 gene. Four basic criteria are required to establish a clinical diagnosis:
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 months of age. The gait abnormality progresses from pelvic limb ataxia to recumbency with opisthotonos, and death occurs within 6 months. 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-months-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 and is most likely due to a mutation in the KIF1C gene, either directly or indirectly. It causes clinical signs that are first noticed between 6 and 36 months of age and progress throughout 1–2 years 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 months old; Romney sheep are affected at 6–18 months of age. Merinos develop a very similar disease at 1–4 years of age. NAD has also been seen in 4- to 7-month-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 months 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-month-old Hafflinger horses in Germany.
Equine degenerative myeloencephalopathy 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 months 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 months of age and progress to recumbency within a few weeks. Widespread (multisystem) neuronal degeneration is seen at necropsy.
Generalized glycogenosis(Pompe disease) 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 months of age. Several loss of function mutations in E1, E13, and E18 are suspected.
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 months old by reducing caloric intake and restricting exercise. Clinical signs typically become apparent from <6 months up to 4 years 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. There are 6 forms of the disease, but OAAM1 is thought to be inherited and due to a deletion mutation (HOXD3/4). 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.
Complex vertebral malformation is a fatal autosomal recessive mutation of SLC35A3 in Holstein cattle and Frieswal bulls. Clinical signs include growth retardation, malformed vertebrae, symmetric arthrogryposis, and occasionally cardiac malformations.
Spinal muscular atrophy is an inherited lower motor neuron (LMN) disorder in Brittany Spaniels that can have an early (by 1 month), intermediate (by 4–6 months), or delayed (>1 year 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 weeks of age, Stockard paralysis (seen in Great Danes crossed with Bloodhounds or Saint Bernards) has an onset at 11–14 weeks, and English Pointers are affected when ~5 months 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 months of age that rapidly progresses to tetraplegia. There is no treatment.
Ataxia of Parson Russell, Jack 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. Some forms also exhibit myokymia (in which the muscles appear to show verminous movement), seizures, or both. Clinical signs begin to appear at ~2–6 months of age, but some forms of the disease are later onset, at approximately 6-12 months of age.
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. In one form of the disease in the Parson Russell, Jack Russell, and Smooth-haired Fox terriers, an autosomal recessive mutation in KCNJ10 has been identified. A mutation in CAPN1 has also been identified in some dogs; however, this may be a rare variant.
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 week. The thoracic limbs become involved over the next 1–2 weeks. A similar condition is seen in young Kooiker dogs (Dutch Decoy dogs) of either sex, with signs beginning at 3–12 months of age. Prognosis is poor in both breeds.
Leukoencephalomyelopathy of Rottweilers has a later onset than neuraxonal dystrophy, usually at ~2–3 years of age. It is possible that the disorders have a similar basis, because animals occasionally may show histopathologic features of both conditions (co-occurrence has been reported in both Rottweilers and Chihuahuas). 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 months 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 radiculopathy may cause lower motor neuron signs in the pelvic limbs, and 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, but many breeds may be affected.
There is no treatment for degenerative myelopathy. Physical therapy slows the progression of clinical signs. A mutation (SOD1) 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. Increased concentrations of a microRNA that regulates genes associated with SOD1 (miR26b) has been associated with progression of 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 months 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, fever, 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, tapered slowly over 6–8 months. Rapid taper may result in relapse. Infectious causes of meningitis should be ruled out.
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.
Recent studies suggest that approximately 80% of neurologically normal Pugs, French bulldogs, and English bulldogs have vertebral malformations. Pugs have a greater likelihood than French bulldogs that malformations will be clinically significant. Decompressive surgery can be successful but often needs to be combined with spinal stabilization.
Caudal articular hypoplasia is reported in Pugs, French bulldogs, and English bulldogs and may cause spinal instability. Surgical stabilization may be beneficial; however, multiple vertebrae are often affected.
Multiple cartilaginous exostosis, seen most commonly in German Shepherds, is a benign proliferation of cartilage or bone that can affect the ribs, long bones, or vertebrae, and may have a familial basis. Treatment consists of surgical removal, but recurrence or occurrence at additional sites is common. 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.
Caudal cervical spondylomyelopathy (wobbler syndrome) may have a heritable basis in Borzois (5–8 years) and Basset Hounds (<8 months) and probably also Doberman Pinschers (≥2 years) and Great Danes (<2 years). Many breeds may be affected. 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. Two forms have been recognized, a disc-associated form (older age of onset), and a facet-associated form (younger age of onset, often giant breeds). 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 or at the level of the facets of the midcervical or caudal cervical vertebrae. Several surgical techniques have been developed, including stabilization, decompression, and disc replacement.
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 diverticuli 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.
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 (eg, spina bifida). The most common cause in dogs is caudal occipital malformation syndrome.
Spinal dysraphism or myelodysplasia includes anomalies of the skin, vertebrae, and spinal cord that are secondary to faulty closure of the neural tube. Generally, this term is used for neural tissues rather than the vertebrae. Where vertebral malformations occur, the condition is generally referred to as spina bifida. Spinal dysraphism is inherited in Weimaraners. Neurologic deficits are evident by 4–6 weeks 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.
Spina bifida or spina bifida occulta is a failure of the vertebral arch to fuse; if the spinal cord is also involved, it is called spina bifida manifesta. Meningomyeloceles may occur with spina bifida. Tethered cord may occur in association with spina bifida. 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. Screw-tail dog breeds are most commonly affected. Spina bifida can also accompany sacrocaudal dysgenesis. Sacrocaudal dysgenesis in Manx cats 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 Ridgebacks but also may occur in other breeds. The sinus is lined by skin and may communicate with the subarachnoid space, causing possible meningitis or myelitis. Treatment consists of surgical excision of the sinus to the level of the dura, and in dogs with bacterial meningitis, longterm antibiotics (minimum 3-month duration) as well. The type of antibiotic should be based on culture and sensitivity when possible, although CSF cultures often fail to yield positive cultures even in the presence of bacteria. Any empiric antibiotic chosen should penetrate the blood-brain barrier, with a preference for bacteriocidal drugs. For young puppies and kittens, trimethoprim sulfa (15–30 mg/kg, PO, twice daily) may be effective, or for older animals a combination of enrofloxacin (in dogs only: 5 mg/kg, PO, twice daily) and amoxicillin-clavulanic acid (11–13.75 mg/kg, PO, twice daily).