Congenital and Inherited Spinal Cord Disorders in Large Animals

Spinal Muscular Atrophy in Large Animals

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 is weakness of the pelvic limbs at the age of 2–6 weeks; calves have difficulty getting up and then become recumbent. Most affected calves are female. A similar disorder occurs in Holstein-Friesian calves (1).

The characteristic sign of this disorder is severe muscle atrophy, especially of the pelvic limbs. Histological evaluation reveals degeneration and loss of motor neurons in the ventral horns of the spinal cord. Neurogenic atrophy of muscles is a consistent lesion.

Spinal muscular atrophy and bovine progressive degenerative myeloencephalopathy might be related, because they occur in the same blood lines. However, the conditions differ in that the onset of BDPME occurs after the age of 5 months, it 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 occurs in horned Hereford cattle in Canada. In this disorder, signs appear soon after birth and include general tremors, incoordination, difficulty standing, and hyperesthesia to tactile stimulation.

A suspected hereditary lower motor neuron disease with accumulation of neurofilaments also occurs in Yorkshire pigs at approximately 5 weeks of age; it is characterized by pelvic limb paresis progressing to recumbency. There is degeneration and loss of motor neurons throughout the spinal cord and brainstem. A similar condition occurs in young Hampshire pigs.

Bovine Progressive Degenerative Myeloencephalopathy

Bovine progressive degenerative myeloencephalopathy (BPDME; weaver syndrome) is an autosomal recessive neurodegenerative disorder of Brown Swiss cattle that occurs in the US, 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 of BPDME:

• onset of bilateral pelvic limb ataxia and dysmetria at the age of 5–8 months

• deficient proprioceptive responses, ataxia in all four limbs, and progressive paraparesis

• normal spinal reflexes and cranial nerve function, and absence of dramatic muscle atrophy

• a familial relationship

BPDME was initially described as “weaver syndrome” because of the peculiar weaving gait of affected animals.

The histopathological changes associated with BPDME are primarily in the sensory nervous system, in contrast to those of spinal muscular atrophy.

Spinal dysmyelination causes congenital lateral recumbency and opisthotonos, but spinal reflexes and alertness are normal.

Simmental Encephalomyelopathy in Calves

Simmental encephalomyelopathy, which occurs in association with behavioral change (eg, aggression or dullness), has an onset in Simmental and Simmental-cross calves at the age of 5–12 months. The gait abnormality progresses from pelvic limb ataxia to recumbency with opisthotonos, and death occurs within 6 months.

Simmental encephalomyelopathy has been reported in the US, the UK, Australia, and New Zealand (2). Characteristic lesions consist of symmetrical necrosis in the caudate nuclei and in other areas of the brain and spinal cord. Similar multifocal lesions (with additional signs of blindness) occur in 1- to 4-month-old Limousin and Limousin-cross calves in Australia and the UK, and in Angus calves in Australia and the US.

Progressive Myelopathy of Murray Grey Cattle

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

Progressive ataxia of Charolais cattle has been reported in the UK and North America (3). It is most likely due to a mutation in the KIF1C gene, either directly or indirectly. Clinical signs 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.

Histopathological lesions of progressive ataxia consist of eosinophilic plaques and myelin breakdown in the white matter of the cerebellum and spinal cord.

Neuraxonal Dystrophy in Large Animals

Neuraxonal dystrophy (NAD) is believed result from a combination of genetic predisposition and vitamin E deficiency early in life. It appears to be inherited in sheep and causes an unsteady, stiff, and swaying gait that progresses to paraparesis and finally tetraparesis. Suffolk and Coopworth sheep are affected as lambs 1–6 months old; Romney sheep are affected at the age of 6–18 months. Merino sheep develop a very similar disease at 1–4 years old. NAD has also been found in Merino lambs 4–7 months old.

Axonal swellings (spheroids) are typically found in gray matter of the brainstem and spinal cord. In older Merino sheep, however, axonal spheroids develop mainly in large white matter tracts of the CNS.

NAD of Morgan horses affecting the lateral (accessory) cuneate nucleus usually develops at the age of 6–12 months and causes spastic paraparesis and pelvic limb ataxia. It is presumed to be inherited.

NAD affecting several brainstem nuclei and causing mild pelvic limb ataxia has also been reported in 4-month-old Haflinger horses in Germany.

Equine Degenerative Myeloencephalopathy

Equine degenerative myeloencephalopathy has been associated mainly with vitamin E deficiency; however, the occurrence of clusters of cases suggest that it might have a familial basis in Appaloosa horses and other breeds.

Degeneration of the spinocerebellar tracts results in a slowly progressive, symmetrical 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

Progressive paresis in Angora goats has been reported in Australia and might have a heritable basis (4).

Clinical signs of spastic paresis and ataxia appear from birth to the age of 4 months and progress to recumbency within a few weeks. Widespread (multisystem) neuronal degeneration is evident at necropsy.

Cervical Stenotic Myelopathy in Large Animals

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. It occurs in young, rapidly growing horses. Thoroughbreds, Tennessee Walking Horses, and warmblood breeds appear to be predisposed, and males are more commonly affected than females.

Overnutrition is an important factor contributing to cervical stenotic myelopathy, and the clinical signs often can be reversed in horses < 9 months old by decreasing 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 in cases of cervical stenotic myelopathy; however, the prognosis for horses that undergo this surgical repair is guarded. In one study, 77% of horses showed neurological improvement, with 46% regaining athletic function (5). Early treatment appears to be associated with improved surgical outcome.

Occipitoatlantoaxial Malformation in Large Animals

Occipitoatlantoaxial malformation (OAAM) is an inherited disorder (autosomal recessive) in Arabian foals; it can also occur in Miniature horse foals, Holstein calves, and lambs. There are six forms of the disease; OAAM1 is thought to be inherited and due to a deletion mutation (HOXD3/4).

Clinical signs of OAAM are progressive ataxia, tetraparesis, and an extended neck posture. Affected foals usually have tetraparesis at birth; however, neurological deficits might not develop for several years. Diagnosis is based on radiography.

Laminectomy has been reported to be successful in some OAAM cases.

Spina Bifida in Large Animals

Spina bifida (sometimes called "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." It occurs in most large animal species.

Spina bifida usually results in dysfunction of the tail and anus, incontinence, and sometimes pelvic limb weakness.

Complex Vertebral Malformation in Large Animals

Complex vertebral malformation is a fatal autosomal recessive mutation of SLC35A3 in Holstein cattle and Frieswal bulls. Clinical signs include delayed growth, malformed vertebrae, symmetrical arthrogryposis, and, occasionally, cardiac malformations.