Oddball neurologic disorders: cats (Proceedings)

Ventroflexion of Neck

This is not really a specific disease but a clinical sign that has several different etiologies: myasthenia gravis, thiamine deficiency, polymyositis, hypokalemia, organophosphate toxicity, hyperthyroidism, hereditary myopathies (Burmese, Devon Rex), hypocalcemia, and portosystemic encephalopathy, polyneuropathy, hypernatremic polymyopathy, ammonium chloride toxicity. Overall, cervical ventroflexion is a sign of generalized neuromuscular weakness in cats.

The chin usually rests near the thoracic inlet, with the eyes positioned dorsally to maintain a straight-ahead gaze. The cat may have a slight protrusion of the dorsal aspects of the scapulae when weight is placed on thoracic limbs. The gait is often stiff and a crouched, wide based stance is often seen in pelvic limbs.

Hereditary Myopathy of Devon Rex Cats

This is a congenital myopathy of Devon Rex cats that was initially described in 1993 by Malik et al. Physical abnormalities can become evident anywhere from 3-23 weeks of age. Signs may include passive ventroflexion of the head and neck, dorsal protrusion of the scapulae, megaesophagus and esophageal weakness, generalized appendicular weakness, and fatigability. Signs are slowly progressive or static. Of the 6 cats originally described, 4 died suddenly of laryngospasm following obstruction of the larynx or pharynx with food.

Serum creatine kinase concentrations are not elevated. Histopathological evaluation of muscle biopsy specimens varies depending on the age of the animal at the time of collection. Dystrophic changes were evident in biopsies collected from older, more severely affected cats. These signs all reflect dysfunction of striated muscle, while skeletal muscle pathology is suggestive of a muscular dystrophy

Feline diabetic neuropathy

In poorly controlled diabetic cats, a distal symmetrical peripheral neuropathy may develop with progressive paraparesis and a plantigrade gait (dropped hocks). Usually both hind limbs are affected, but some cases are unilateral. Clinical signs may progress to also involve the thoracic limbs. The reported clinical incidence of neurologic signs is 8% although the true incidence may be much higher.

Mizisin AP, Shelton GD, Burgers ML, et al. J Neuropathol Exp Neurol 2002;61:872-884: "Functional, structural, and biochemical defects were detected in diabetic cat peripheral nerves compared to nondiabetic cats. A sensory and motor neuropathy was present in diabetic cats' pelvic and thoracic limbs. Motor nerve conduction was more impaired than sensory nerve conduction and the pelvic limb was more affected than the thoracic limb. Few electromyographic abnormalities were found. Histological changes included Schwann cell injury and myelin defects. Nerve fructose increased with sorbitol accumulation."

Strict glycemic control reverses the clinical signs of neuropathy in some, but not all, cats. The reason that some cats don't improve is not known. Experimental treatments: Acetyl-l-carnitine, 50 mg amino guanidine BID, methylcobalamin (? 3mg/cat/day PO?)

Spinal Muscular Atrophy in Maine Coon Cats

Spinal muscular atrophies are a group of inherited disorders characterized by degeneration of lower motor neurons, resulting in progressive paresis to paralysis of voluntary skeletal muscles. Affected Maine coon kittens appear clinically normal until 15-17 weeks at which time pelvic limb weakness and fine generalized tremors are noted. Affected kittens may lose the ability to jump by 5-12 months of age and walk with a pelvic limb sway. Stance is abnormal with hocks nearly touching and hind feet pointing out at an angle from midline of 30-40(. Hyperesthesia may also be identified over the lumbar spine.

Affected cats also have elevation of serum CPK activity to 2-3 times normal. Neurogenic atrophy of muscle is found on biopsy. The weakness and muscle wasting is slowly progressive; however, not incompatible with an acceptable quality of life for a variable number of years as indoor pets.

The disorder is an autosomal recessive degeneration of motor neurons that results in weakness. Dr. John Fyfe at Michigan State University has done most of the work in identifying this disease.

His lab has developed a DNA test (using cheek brushing cells) to identify carriers: Laboratory of Comparative Medical Genetics at Michigan State University. http://mmg.msu.edu/faculty/fyfe/fyfeSMAtesting.pdf

Feline Hyperesthesia Syndrome

Feline hyperesthesia syndrome is an unusual condition because the demonstrated behaviors may actually be triggered by different factors (fleas, behavioral disorders, myositis, seizures, etc). These behavioral changes can include those mimicking estrus or biting at the tail, flank, anal or lumbar areas often accompanied by vocalization, running, jumping or apparent hallucinations. Affected cats often have noticeable dorsal skin ripples that may occur spontaneously or may induced by grooming or petting. Extreme cases may exhibit paddling, involuntary urination and defecation, changes consistent with seizure activity. Some cats will exhibit a range of self-mutilation from excessive licking, to plucking (trichotillomania), barbering, biting, and chewing that lead to skin lesions. Thus signs overlap with behavioral, neurological, and dermatological systems. It is sometimes difficult to distract the cat from the behavior.

It is important to eliminate flea allergy, painful spinal or muscular problems, and dermatological causes as etiologies before considering the possibility of a seizure or behavioral disorder. Environmental and social stresses have been associated with feline hyperesthesia and range from readily apparent skin conditions (including food allergy, atopy, or fleas) to changes in household (the addition or loss of another cat or human; intercat aggression).

A few cases have had a muscle condition called inclusion body myositis. Pathologic changes found on biopsy of paraspinal muscles have included inflammation and vacuoles within the myofibers. In people, this is thought to be an immune-mediated disease similar to polymyositis. Supplements that might improve signs of inclusion body myositis include Acetyl-L-Carnitine 50mg/kg every 12 hours; CoEnzyme Q10 1mg/kg once daily; Riboflavin 50mg once daily; Vitamin E 20 IU/kg once daily. Allow one month to see if beneficial.

Haws Syndrome

Haws syndrome is characterized by elevation of the third eyelids. It is likely an autonomic imbalance, associated most frequently with gastrointestinal (GI) inflammation/ disease. In England, Haws syndrome has been associated with Toro virus infection of the GI tract in cats. Other GI conditions that have been associated with Haws: internal parasites, dietary hypersensitivity, inflammatory bowel disease, pancreatitis.

Most cats with haws seem to have mild GI signs, usually a chronic low-grade diarrhea, and often-mild dehydration.

Most cases resolve in several weeks, but it isn't known if treatment of the GI disease results in resolution or if the signs just spontaneously resolve. Some cases will linger for a few months.

Feline Ischemic Encephalopathy (FIE)

Ischemic encephalopathy is an acute ischemic necrosis of brain tissue usually involving the areas of the brain that are supplied by the middle cerebral artery. Clinical signs are sudden in onset. Initially, the neurologic signs might be generalized, but as the edema subsides a more focal effect is seen and unilateral motor and sensory deficits can usually be found. Seizures, blindness, behavioral changes and asymmetric motor abnormalities are a frequent consequence. Signs usually stabilize and sometimes regress after a few days. But some cats may have residual periodic seizures (acquired epilepsy) or permanent behavioral changes such as mental dullness or aggression. It is theorized that ischemic encephalopathy may be a common cause of acquired epilepsy in the cat.

Historically, this disease has seemed to be more prevalent in the eastern United States. It occurs more commonly in the summer months.

Recent histopathology has demonstrated parts of Cuterebra larvae in the affected brain area , which may explain the prevalence in the summer months. In some cases, there has been a history of recent upper respiratory infection suggesting that the larvae might enter via the cribiform plate. Larva migration may cause a vasospasm resulting in ischemia or may be toxic in nature. Other causes for the ischemia may eventually be found to explain the cases seen at other times of the year.

Feline Cerebellar Hypoplasia

Feline cerebellar hypoplasia is caused by in utero infection with the panleukopenia virus (parvovirus), which has a predilection for actively dividing cells. The virus affects the external germinal layer of the cerebellum, preventing the formation of the granular layer and which results in atrophy. Some affected cats have a concurrent hydrocephalus and hydranencephaly.

The queen is usually asymptomatic for the infection; only the developing cells of the kitten are affected. Some kittens may be born dead; others will have signs of cerebellar degeneration that become noticeable when the kittens first start to ambulate. Not all kittens in a litter from a parvovirus-infected queen will show signs of cerebellar disease and the severity of signs can vary.

The clinical signs are of a diffuse cerebellar disease. Signs are non-progressive which distinguishes cerebellar hypoplasia from cerebellar abiotrophy, storage diseases (GM1 and GM2 gangliosidosis, mannosidosis, sphingomyelinosis) and infections (toxoplasmosis and feline infectious peritonitis).

History and clinical signs support diagnosis. Magnetic resonance imaging may help to define the nature of the lesion. No treatment is helpful.

Another cause of cerebellar hypoplasia is the administration of a modified live panleukopenia vaccine during the later stages of pregnancy. Modified live panleukopenia virus vaccine should be avoided in the pregnant cat.