Inflammatory and Infectious Diseases of the Spinal Column and Cord

Discospondylitis is inflammation of the intervertebral disc and adjacent vertebral bodies. Vertebral osteomyelitis is inflammation of the vertebra without concurrent disc infection. Both diseases are usually caused by hematogenous spread of bacterial or fungal infection. Immunosuppression may play a role in some infections. Discospondylitis is most common in dogs, especially larger breeds. Osteomyelitis of the lumbar vertebrae can develop in dogs secondary to migration of plant awns. In cats, it is rare and usually due to direct spread of infection from an adjacent wound. Discospondylitis and vertebral osteomyelitis have also been reported in horses, ruminants, and pigs, especially neonates. Infection may be seen at any disc space, and multiple lesions may be seen.

In canine discospondylitis, the most commonly isolated organisms are Staphylococcus spp. Other organisms include Brucella canis, Streptococcus spp, Escherichia coli, Proteus spp, Corynebacterium diphtheroides, Nocardia spp, and Aspergillus spp. Spinal pain is the most consistent clinical finding. Systemic signs, such as fever, depression, and weight loss, are less common. Neurologic deficits may develop due to spinal cord compression caused by proliferative tissue or, rarely, spread of infection to the spinal cord or pathologic fracture.

Early radiographic findings consist of destruction of the adjacent vertebral end plates and collapse of the disc space. More advanced lesions also have variable degrees of osteophyte formation. Blood and urine cultures often identify the causative organism. Affected dogs should be tested for brucellosis (see Brucellosis in Dogs).

Although clinical signs usually resolve within 5 days of treatment with an appropriate antibiotic, treatment should be continued for at least 8 wk. Amoxicillin/clavulanic acid for presumed Staphylococcus spp infection is a good choice if cultures are negative.

Neurologic abnormalities, including signs of spinal cord dysfunction, are sometimes seen in dogs with rickettsial infection. Dogs with Rocky Mountain spotted fever (Rickettsia rickettsii, see Rocky Mountain Spotted Fever) often have thrombocytopenia, leukocytosis, and a neutrophilic pleocytosis and mildly increased protein on CSF analysis. Diagnosis is based on a 4-fold increase in serum antibody concentration. Dogs with ehrlichiosis (Ehrlichia canis, see Ehrlichiosis and Related Infections) often have thrombocytopenia, anemia, leukopenia, hyperglobulinemia, and mononuclear pleocytosis and marked increase in protein on CSF analysis. A single serum antibody titer is usually sufficient for diagnosis of E canis. Treatment of rickettsial myelitis consists of doxycycline or chloramphenicol for 14–21 days. Prognosis is good with early treatment, although neurologic deficits occasionally progress despite treatment.

Canine distemper encephalomyelitis (see Canine Distemper), caused by a paramyxovirus, remains one of the most common CNS disorders in dogs worldwide. Onset of neurologic deficits may be acute or slowly progressive, reflecting the location of the lesion(s) within the CNS. The brain stem and spinal cord are the regions most commonly affected in mature dogs. Neurologic signs are usually not preceded by, nor coincident with, the systemic illness seen in young dogs.

Definitive antemortem diagnosis is difficult. There may be active or inactive chorioretinitis on fundoscopy. A lymphocytic pleocytosis with increased protein concentration is the most common finding on CSF analysis. Reverse transcriptase-PCR on urine or CSF is useful in diagnosis. There is no specific treatment, and the prognosis is poor for severely affected dogs. Vaccination is usually successful in preventing the systemic form of distemper, but previously vaccinated dogs can be affected by the neurologic form.

Caprine arthritis and encephalomyelitis (see Caprine Arthritis and Encephalitis) is caused by a lentivirus that can also cause pneumonitis and arthritis. CNS disease is most common in goats 2–4 mo old, although older animals may also be affected. There is an acute onset of slightly asymmetric spastic paraparesis that may progress to tetraplegia with exaggerated reflexes. A mononuclear pleocytosis and increased protein in the CSF are present in ~50% of the cases. Serologic testing is helpful in detecting infection, but false-negatives can be seen. Histologically, there is severe nonsuppurative inflammation with demyelination or necrosis, most prominent in the white matter of the spinal cord. There is no treatment, and recovery is unlikely.

A related lentivirus is a rare cause of chronic encephalomyelitis in sheep (maedi, see Progressive Pneumonia in Sheep and Goats). Affected sheep are usually >2 yr old and suffer an insidious onset of progressive ataxia, paraparesis, or tetraparesis.

Equine infectious anemia (see Equine Infectious Anemia) occasionally produces encephalomyelitis in horses. Neurologic deficits are usually referable to spinal cord disease and include ataxia and weakness in the hindlimbs. The protein concentration of and the number of lymphocytes in the CSF are often increased. Diagnosis is by positive agar gel immunodiffusion testing. There is no treatment, and affected horses are usually euthanized to prevent spread of the disease.

Equine herpesvirus 1 (EHV-1) encephalomyelopathy is a neurologic disorder that affects horses worldwide. The EHV-1 virus infects vascular endothelial cells, particularly those within the CNS, and causes an immune-mediated vasculitis with secondary infarction and hemorrhage throughout the brain and spinal cord. The EHV-1 virus has also been associated with meningoencephalitis in alpacas and llamas. In horses, neurologic signs may be seen as the primary disease or follow rhinopneumonitis or abortion. Any age animal may be affected.

Neurologic deficits have an abrupt onset, vary from mild hindlimb ataxia to paraplegia, and usually do not progress after 24 hr. Urine dribbling, fecal retention, and sensory deficits in the perineum and tail are common. The CSF is often xanthochromic with increased protein content and normal numbers of cells. Diagnosis is based on clinical findings and an increase in antibody concentration in paired serum samples, isolation of virus from nasal or pharyngeal secretions, or PCR testing. There is no specific treatment, but anti-inflammatory agents such as dimethyl sulfoxide, dexamethasone, and NSAIDs may help. Supportive care is important to prevent complications such as urine retention, cystitis, and decubitus. Mildly affected horses often recover with supportive care. Even recumbent horses can eventually recover with meticulous nursing care. Vaccination does not protect from the neurologic form of this disease. (Also see Equine Herpesvirus Infection.)

Feline infectious peritonitis (see Feline Infectious Peritonitis) is a disease of domestic cats caused by an immune-mediated response to a coronavirus. CNS involvement is common. There are pyogranulomatous lesions involving the neural parenchyma, choroid plexuses, ependyma, and leptomeninges. Clinical signs of spinal cord involvement include spinal hyperesthesia and paraparesis or tetraparesis. Hyperglobulinemia and involvement of other organs, especially the eyes, are common. Serum antibody tests currently available are insensitive and nonspecific. A mixed (neutrophilic and mononuclear) pleocytosis with increased protein concentration is the most common finding on CSF analysis. There is no effective treatment, and prognosis is poor.

Feline leukemia virus–associated myelopathy is seen in some cats infected with the feline leukemia virus (FeLV, see Feline Leukemia Virus and Related Diseases) for ≥2 yr. Ataxia and weakness of the pelvic limbs progresses to paraplegia within 1 yr. Other signs include diffuse spinal pain and abnormal behavior. Diagnosis is based on clinical features, FeLV serology, and exclusion of other causes, such as spinal lymphoma and myelitis due to toxoplasmosis or fungal infection. There is no treatment; affected cats are eventually euthanized because of disability. Pathologic findings consist of white matter degeneration, swollen axons, and dilation of myelin sheaths in the spinal cord and brain stem. FeLV antigen is present in the nervous system, indicating that the lesions are due to viral infection.

Teschovirus encephalomyelitis (see Teschovirus Encephalomyelitis), also called Teschen disease, Talfan disease, and porcine polioencephalomyelitis, is caused by a neurotropic teschovirus previously classified as an enterovirus. There is a peracute or subacute onset of hindlimb ataxia and paresis with hyporeflexia, depression, seizures, and death. Older pigs may survive, but mortality is high in young pigs.

Porcine hemagglutinating encephalomyelitis virus is a coronavirus that causes both vomiting and wasting disease (see Porcine Hemagglutinating Encephalomyelitis) and an encephalomyelitis. It is most common in piglets <3 wk old, and there is some overlap of these syndromes. The CNS disease starts with several days of vomiting, which is followed by hyperesthesia, muscle tremors, ataxia, paresis, opisthotonos, coma, and death. Histopathologically, there is diffuse nonsuppurative encephalomyelitis, primarily involving gray matter. Diagnosis is based on necropsy or an increase in antibody titer in paired sera. There is no treatment.

Rabies (see Rabies) is caused by a neurotropic rhabdovirus that reaches the CNS via peripheral nerves. It produces multifocal, nonsuppurative polioencephalomyelitis in all domestic mammals. Signs of spinal cord involvement include ataxia and progressive paralysis, usually with absent reflexes. Affected animals typically, but not invariably, die with progressive neurologic signs within 2–7 days of illness.

Cryptococcus neoformans is the most common fungus to involve the CNS in animals. Infection is most common in dogs and cats and occurs occasionally in horses. Other fungal organisms may invade the CNS, including Blastomyces dermatitidis, Histoplasma capsulatum, Coccidioides immitis, Aspergillus spp, and phaeohyphomycoses. Affected animals often have involvement of other organs, such as the lungs, eyes, skin, or bones. Signs of spinal cord involvement include paresis or paralysis and spinal hyperesthesia. Diagnosis is based on serology, culture, or identifying the organism in CSF or extraneural tissue. Fluconazole is often effective for cryptococcosis and coccidioidomycosis. Itraconazole or amphotericin B is recommended for histoplasmosis and blastomycosis, but the prognosis is guarded to poor. (Also see Fungal Infections.)

Equine protozoal myeloencephalitis (see Equine Protozoal Myeloencephalitis) is a common disease of horses that produces a nonsuppurative, often necrotizing, meningoencephalomyelitis. Horses are likely an aberrant host for the causative organism, usually Sarcocystis neurona, but less commonly, other protozoa cause the disease. Neurologic signs are extremely variable and often asymmetric, reflecting involvement anywhere in the CNS. Ataxia and paresis are common. Other potential signs include obscure lameness, focal muscle atrophy, and cranial nerve dysfunction. Approximately 75% of affected horses improve with treatment, but permanent neurologic deficits are possible and relapse is not rare.

Neosporosis (see Neosporosis) is caused by Neospora caninum, a protozoan that can cause a nonsuppurative encephalomyelitis, most commonly in dogs. Infection in young puppies typically causes ascending paralysis with rigid contraction of the muscles of one or both pelvic limbs. Other organs, including muscle, liver, and lungs, can be affected. Diagnosis is based on detection of antibodies to the organism by immunohistochemistry or PCR. Early treatment with clindamycin or sulfadiazine and pyrimethamine may be effective, but the prognosis is poor.

Toxoplasmosis (see Toxoplasmosis) is caused by Toxoplasma gondii and can occasionally cause a nonsuppurative encephalomyelitis in puppies, kittens, and piglets. Diagnosis is based on identifying the organism in tissue or a 4-fold increase in IgG antibody in paired sera. In cats, a high concentration of IgM antibody in serum or CSF supports the diagnosis. Clindamycin or sulfadiazine and pyrimethamine are recommended for treatment.

Verminous myelitis is inflammation of the spinal cord caused by parasite migration. Organisms include Parelaphostrongylus tenuis in sheep, goats, and llamas; Hypoderma bovis in cattle; Strongylus vulgaris, Halicephalobus deletrix, and Setaria spp in horses; Stephanurus dentatus in pigs; Cuterebra spp in cats; and Baylisascaris procyonis in dogs. Signs of spinal cord involvement are usually acute, often asymmetric, and may be progressive. Antemortem diagnosis is difficult. Increased eosinophils in the CSF is suggestive, but CSF findings are variable. Treatment with fenbendazole, thiabendazole, or ivermectin is recommended, but the prognosis is guarded. (Also see CNS Diseases Caused by Helminths and Arthropods.)

Feline nonsuppurative meningoencephalomyelitis (feline polioencephalomyelitis, staggering disease) is a slowly progressive, inflammatory disease of the CNS in domestic cats. It has been reported in North America, Europe, and Australia. The cause is unknown, but an infectious agent, probably a virus, is strongly suspected. The disease causes neuronal degeneration, axonal loss, and demyelination with mononuclear inflammation, most severe in the thoracic segments of the spinal cord. The clinical course is marked by progressive paraparesis of 1–2 mo duration, often with focal hyperesthesia, head tremor, and behavioral changes. Antemortem diagnosis is difficult. There is no treatment, and prognosis is poor.

Granulomatous meningoencephalomyelitis (GME) is an inflammatory disease of the CNS in dogs worldwide. The cause is unknown, although an infectious agent, most likely a virus, is suspected. In the disseminated form, previously called inflammatory reticulosis, there are perivascular accumulations of mononuclear cells and neutrophils. In the focal form, previously called neoplastic reticulosis, there are granulomatous lesions containing primarily reticulohistiocytic cells. Adult dogs of any breed can be affected, but female, small-breed dogs, especially Poodles, may be predisposed.

Clinical signs are variable and may indicate focal or multifocal brain or spinal cord dysfunction. Cervical pain and tetraparesis are the most common signs of spinal cord involvement. Signs are often acute, but the focal form of GME can cause neurologic deficits that slowly progress over the course of several months. The CSF usually has increased protein and pleocytosis, with either mononuclear cells or neutrophils predominating. MRI and CT often show a single or multiple enhancing masses. Tentative diagnosis is based on clinical findings, imaging, CSF analysis, and exclusion of other possible diseases. Dogs often improve with immunosuppressive doses of corticosteroids and other immunomodulating drugs such as cytarabine, cyclosporine, and procarbazine, but relapse is possible, and many dogs eventually become refractory to treatment.