Cats are affected with specific spinal cord disorders and common 'canine' spinal disorders are uncommon in cats. Cats should not be considered small dogs and it is important to consider a different diagnostic approach in cats with suspected spinal disease. The most common spinal disorders in cats are (1) inflammatory disease, particularly feline infectious peritonitis virus, (2) neoplastic disease, particularly spinal lymphoma, and (3) external trauma.¹ Although by definition not a spinal disorder, arterial thromboembolism is another important cause of acute paralysis in cats.

Arterial Thromboembolism

This devastating disorder should be considered in every cat with acute onset paralysis. Cats typically present with a neuromyopathy caused by embolization of the distal aorta. The clinical presentation is almost pathognomonic and is based on recognition of the five 'Ps': pain, paralysis, pulselessness, poikilothermy, and pallor.² This condition is often associated with advanced heart disease and carries a poor prognosis. If treatment is attempted, therapy includes (1) analgesia, (2) management of present congestive heart failure, and (3) antithrombotic treatment. Many cats are, however, euthanized at the time of diagnosis, less than 40% of treated cats survives until discharge, and half of surviving cats will experience a recurrence of disease.²

Feline Infectious Peritonitis Virus

Feline infectious peritonitis (FIP) virus is caused by the virulent biotype of feline coronavirus. Neurologic signs are usually associated with the dry form, are progressive in nature, and usually not limited to a spinal cord localisation. Multifocal central nervous system involvement is common and ocular abnormalities, such as chorioretinitis, can also be seen in combination with neurological signs. Although FIP is a systemic disease, general physical abnormalities, such as pyrexia. Lethargy and weight loss are not always present.³ Although FIP can affect cats of every age, affected animals are usually younger than 2 years of age. Male cats are overrepresented and although purebred cats have been considered more vulnerable, recent studies do not demonstrate a strict breed predilection.³ Obtaining an antemortem diagnosis of FIP is challenging. Although FIP is associated with certain MRI abnormalities, this diagnostic technique is not widely available. An antemortem diagnosis can be obtained by tissue biopsy or evaluation of body cavity effusions, in which positive immunofluerescent staining of feline coronavirus antigen in macrophages can be considered conclusive. Evaluation of tissue biopsies and body effusions is unfortunately not feasible in most cats with neurological FIP because (1) disease in animals with neurological disease is often limited to the central nervous system, and (2) affected animals with neurological signs are most often affected by the dry form of FIP. Nonspecific haematological and biochemistry abnormalities include leucocytosis, lymphopenia, microcytosis, nonregenerative anaemia, hyperbilirubinemia, hypoalbuminaemia, and increased total serum protein caused by hyperglobulinaemia. Hyperglobulinaemia and decreased albumin/globulin (A:G) ratios have been suggested to have higher diagnostic value than hyperproteinaemia.³ Total protein is increased in only 17.5% of cats with FIP overall (and 33% of cats without effusion), while hyperglobulinaemia has been documented in 89% of cats with FIP.³ Decreased A:G ratios, varying between <0.6 and <0.8, have been suggested to be of diagnostic value in cats with suspected FIP.³ FIP and the harmless feline enteric coronavirus cannot be distinguished genetically. Serum antibody detection is therefore of limited use because a high percentage of healthy cats have antibodies against feline coronavirus and will never develop FIP. For the same reason should detection of feline coronavirus in whole blood or serum by real-time polymerase chain reaction (RT-PCR) be considered unreliable to definitely diagnose or exclude FIP. The potential for false positive results is especially concerning for RT-PCR on whole blood or serum.¹ RT-PCR has diagnostic value in differentiating FIP effusions from other types of effusions, which is not helpful in most cats with neurological disease who generally suffer from the dry form of FIP. RT-PCR on cerebrospinal fluid (CSF) of cats with neurological disease has been reported to have a high specificity, sensitivity, and positive predictive value for FIP and can therefore be considered in neurologically abnormal animals (but not in neurologically normal).⁴ CSF analysis can further demonstrate a high protein content and pleocytosis with a predominance of neutrophils or lymphocytes. FIP is a fatal disease with no effective treatment available, and the median survival time is 9 days.

Neoplasia

Neoplasia is the second most common feline spinal disorder with lymphoma being the most common tumour.^1,5 Osteosarcoma, glial tumours, and meningioma are other common spinal tumours in cats.⁵ Although animals with spinal tumours are generally older, cats with spinal lymphoma are significantly younger than cats with other spinal tumours. Cats with spinal lymphoma have a bimodal age distribution with 50% reported to be younger than 4 years of age and 25% older than 11 years.⁵ This indicates that spinal tumours should also be considered in younger cats. Approximately half of cats with spinal lymphoma have a FeLV positive status and 85% have postmortem findings of extraneural involvement with kidneys and bone marrow being most often affected.⁵ Affected cats can therefore suffer from other non-specific clinical signs such as anorexia, lethargy, weight loss, and respiratory tract disease. Although making a definitive diagnosis requires taking surgical biopsies, this is often not feasible for tumours affecting the spinal cord. A suspicion of osteosarcoma can be obtained by visualisation of osteolytic lesions or pathological spinal fractures on radiographs. Spinal lymphoma can be diagnosed by positive cytology on blood smears, bone marrow, cerebrospinal fluid, or obtaining fine needle aspirate biopsies of identified extraneural sites.⁵ Advanced diagnostic imaging, such as myelography or MRI allows better identification of the mass lesion and its relationship to the spinal cord. Prognosis of spinal neoplasia should be considered poor. Treatment is dependent on the type of tumour and can include chemotherapy, decompressive surgery with cytoreduction, or radiation therapy. Lymphoma tends to be variably responsive to chemotherapy, while surgery can result in prolonged survival times in spinal meningioma.

Other Spinal Cord Conditions

As stated above, disorders commonly affecting the canine spinal cord, occur only rarely in cats. Although intervertebral disc disease (IVDD) is the most common spinal cord condition in dogs with 2–3% of the overall canine population affected, this condition only affects 0.2% of cats.⁶ Similarly, although fibrocartilaginous embolism and acute non-compressive nucleus pulposus extrusions (also called high-velocity low-volume intervertebral disc extrusions or traumatic intervertebral disc extrusions) are common spinal emergencies in dogs, these conditions are uncommon in cats. Treatment and prognosis for these conditions are comparable in dogs and cats and is largely dependent on severity of spinal cord dysfunction.^7,8

Approach to Feline Spinal Cord Conditions

As illustrated above, the most common feline spinal cord conditions can be considered neurological consequences of systemic disease. It is therefore important to not only focus on the spinal signs, but also on other body systems. Even more so than in dogs, the results of a thorough clinical history, complete clinical examination and a 'medical diagnostic work-up' can provide valuable information. Cats with lymphoma and FIP can present with other non-specific clinical signs such as lethargy, anorexia, weight loss and multifocal neurological signs.

Cats with FIP can present with pyrexia, while ATE can be associated with hypothermia. Decreased femoral pulses and abnormal thoracic auscultation are often present in cats with ATE. Thorough abdominal palpation and an ophthalmologic examination can reveal extraneural involvement in cats with FIP and spinal lymphoma. A blood smear, haematology, biochemistry profile, and evaluation of FeLV status should always be considered in cats with spinal disease. Thoracic radiographs and abdominal ultrasound can provide further evidence of extraneural FIP or lymphoma. Finally, a bone marrow biopsy can be considered in cats suspected of spinal lymphoma.

References

1.  Marioni-Henry K, Vite CH, Newton AL, Van Winkle TJ. Prevalence of diseases of the spinal cord of cats. J Vet Intern Med. 2004;18:851–858.

2.  Luis Fuentes V. Arterial thromboembolism: risks, realities and a rational first-line approach. J Feline Med Surg. 2012;14:459–470.

3.  Riemer F, Kuehner KA, Ritz S, Sauter-Louis C, Hartmann K. Clinical and laboratory features of cats with feline infectious peritonitis - a retrospective study of 231 confirmed cases (2000–2010). J Feline Med Surg. 2016;18:348–356.

4.  Doenges SJ, Weber K, Dorsch R, et al. Detection of feline coronavirus in cerebrospinal fluid for diagnosis of feline infectious peritonitis in cats with and without neurological signs. J Feline Med Surg. 2016;18:104–109.

5.  Marioni-Henry K, Van Winkle TJ, Smith SH, Vite CH. Tumors affecting the spinal cord of cats: 85 cases (1980–2005). J Am Vet Med Assoc. 2008;232:237–243.

6.  De Decker S, Warner AS, Volk HA. Prevalence and breed predisposition for thoracolumbar intervertebral disc disease in cats. J Feline Med Surg. 2016; pii:1098612X16630358.

7.  Taylor-Brown FE, De Decker S. Presumptive acute non-compressive nucleus pulposus extrusion in 11 cats: clinical features, diagnostic imaging findings, treatment and outcome. J Feline Med Surg. 2015; pii: 1098612X15605150.

8.  Theobald A, Volk HA, Dennis R, Berlato D, De Risio L. Clinical outcome in 19 cats with clinical and magnetic resonance imaging diagnosis of ischaemic myelopathy (2000–2011). J Feline Med Surg. 2013;15:132–141.