As all clinicians well know, cats are not just small dogs! Whereas the basic principles of history taking, physical examination, neurological examination etc. apply in both species, the diseases that lead to neurological signs differ. Clinicians must be aware of these differences when approaching a case and discussing interventions with owners.
Tetraparesis and Tetraplegia
A cat with neurological deficits in all four limbs may have a lesion at any of the following locations:
Cervical spine (C1-C5)
Cervicothoracic spine (C6-T2)
Differentiation is based on the findings of the neurological examination.
Paraparesis and Paraplegia
There are several conditions that must be considered in the acutely paralyzed cat. Trauma, ischaemic neuromyopathy (aortic embolism) and neoplasia are the most important. In more chronic cases, neoplasia and disc-related conditions are more likely. Disc disease is being recognized more frequently.
Trauma usually results from road accidents. Most cases are readily recognized by historical or physical information, but accurate client information regarding trauma is relatively less common in cats than in dogs. Radiography will confirm the diagnosis. Many cats respond well to conservative treatment by cage rest or application of a body cast. Surgical intervention may be appropriate if there is myelographic evidence of cord compression, the fracture is unstable or the cat is in severe pain.
Ischaemic neuromyopathy (aortic thromboembolism) is a common cause of acute paraplegia in cats. Acute paraplegia, areflexia, absent pain sensation, cold limbs, absent femoral pulses and swollen painful gastrocnemius muscles are the most common features. Affected cats have cold extremities in the hindlimbs, with cyanotic nail beds and toes that do not bleed with needle prick. Occasional cats have signs referable to renal, gastrointestinal or other dysfunction. Diagnosis is based on the characteristic clinical signs. Preexisting cardiomyopathy underlies the thromboembolic episode, but the presence of a thrombus does not entirely explain the clinical signs. There appears to be a failure of collateral circulation because of release of vasoactive substances from the area of the thrombus.
Neoplasms of the spinal cord and associated structures are common in cats. Lymphosarcoma is the most prevalent; vertebral tumors are rare. Most cases of spinal lymphosarcoma occur in cats less than 3 years old, and the progression of the clinical signs is relatively acute. Thus, neoplasia must be considered in all cats, regardless of age or acuteness of signs. Thoracic and lumbar tumors are most common, causing neurological signs in the hindlimbs.
Diagnosis of spinal tumors in cats depends largely on myelography. Plain radiographic abnormalities are unusual. Occasional tumors involve the vertebrae. In some cases of lymphosarcoma, a soft tissue mass is visible in the thorax, ventral to the area of the spine involved. Cerebrospinal fluid may be abnormal but is unlikely to provide definitive information. In spinal lymphosarcoma, systemic signs are usually not apparent, but the vast majority of these cats are FeLV-positive.
Disc disease and discospondylitis--disc protrusions occur frequently in cats, but clinical signs related to spinal cord compression are comparatively rare. Cats with myelographic evidence of spinal cord compression should have decompressive surgery. Discospondylitis is rare in cats and is generally seen with other manifestations of infection, for example, subcutaneous abscesses.
Congenital spinal deformities--spina bifida is seen occasionally in cats, particularly in the Manx breed.
Ischaemic myelopathy causing peracute, asymmetrical neurological deficits is rare in cats. The diagnosis is based on the absence of a compressive lesion on myelography. Conservative treatment is indicated.
Peripheral Nerve, Neuromuscular Junction and Muscle
Diabetic neuropathy occurs in some cats with diabetes mellitus. Affected cats are paraparetic with a plantigrade stance. Definitive diagnosis of polyneuropathy requires electrophysiological evaluation.
Inherited hyperchylomicronaemia causes peripheral neuropathy. Peripheral nerves are compressed by the lipid granulomas that develop. The condition may improve if the hyperchylomicronaemia is reduced.
Ischaemic neuromyopathy is the most common peripheral neuropathy in cats, but the clinical signs of acute paraplegia are initially more suggestive of spinal disease--see above.
Neuromuscular Junction Disorders
Myasthenia gravis may cause typical episodic weakness related to exercise, regurgitation, muscle tremors, dysphonia and neck flexion. Aspiration pneumonia may develop with megaoesophagus. Both congenital and acquired forms of the disease are seen, and Abyssinian and related breeds may have a relatively high incidence. The diagnosis is based on the clinical signs and may be confirmed by the intravenous administration of edrophonium hydrochloride (0.25-0.5 mg I.V.)--"the edrophonium response test." Here, cats with acquired myasthenia gravis rapidly become normal for a period of several minutes. The disease is immune-mediated, with antibodies directed against the acetylcholine receptor. Treatment with pyridostigmine hydrochloride (0.5-3.0 mg/kg/per day by mouth) and corticosteroids is indicated.
Potassium-depletion myopathy is the most commonly recognized muscle disease of cats reported during recent years. Affected cats show acute muscle weakness with a typical posture of neck flexion and the head carried low. The gait is stilted and the cats are reluctant to walk. Muscles may be painful on palpation and exercise induces collapse.
Differential diagnosis includes myasthenia gravis, polymyositis and generalized polyneuropathy. The diagnosis is confirmed by demonstrating a low serum potassium (less than 3.0 mEq/l) in a clinically affected cat. Other causes of hypokalemia, for example, alkalosis, hyperinsulinaemia or recent fluid therapy, must be eliminated. Creatine kinase concentrations are usually elevated.
Treatment depends on the severity of the clinical signs. Severely affected cats require aggressive intervention but care must be taken. Administration of fluids can cause a rapid decline in the condition and even result in respiratory paralysis. Careful intravenous potassium supplementation is required. When the crisis is resolved, or in less severely affected cats, oral potassium supplementation is adequate with potassium gluconate. If renal insufficiency if present, oral potassium supplementation is required for life. The prognosis for recovery of muscle function is good.
Polymyositis is rare in cats. Typical clinical signs of stiffness, weakness and painful muscles may be seen in Toxoplasmosis or in cats with idiopathic polymyositis.