SCIENTIFIC FEATURE OF THE MONTH

Epileptic seizures can occur as reactive seizures secondary to metabolic or toxic conditions, symptomatic seizures caused by structural brain disease, or seizures with no identifiable cause (idiopathic epilepsy). Idiopathic epilepsy is considered to be rare in cats, with the most reports originating from Europe. A genetic basic fpr idiopathic epilepsy in cats has not been established.

A recent retrospective study evaluated 91 of the 164 cats presenting for seizure disorders at a veterinary teaching hospital in Europe from 2000 through 2004. The purpose of the study was to analyze and classify associations among etiologic factors contributing to seizures and signalment, clinical signs, and outcome in the 91 cats that had sufficient data for entry into the study.

Data regarding characteristics of the cats and their seizures were obtained from medical records. Over the 5-year period, the incidence of seizures among all the cats evaluated at the hospital was 2.1%. The etiology of the seizures was classified as symtomatic in 45 (50%), idiopathic or presumed idiopathic in 23 (25%), reactive in 20 (22%) cats, and cardiac syncope in 3 (3%).

Focal seizures with or without secondary generalization were recorded for 47 (52%) cats, and primary generalized seizures with or without status epilepticus were recorded for 44 (48%). Etiology was not associated with seizure type. The age at first seizure ranged from 1 week-19 years. However, the mean age of cats with idiopathic seizures (3.5 Yrs) was significantly lower than that of cats with reactive seizures (8.2 yrs.) or symptomatic seizures (8.1 yrs). Of the 91 cats, 53 (58%) were males, 45 castrated, and 38 (42%) were females, 31 spayed. Most were domestic shorthairs (78), 6 were Maine coon, 4 were Siamese, and there was 1 cateach for Persian, British shorthair, and Devon Red breeds. 70% of the cats were evaluated within 1 week of their initial seizure. The 1-year survival rate for cats with idiopathic seizures (0.82) was no longer than that for cats with reactive(0.50) or symptomatic (0.16) seizures.

Symptomatic seizures were present in 45 of the 91 cats, and included inflammatory, neoplastic, traumatic, or vascular causes. Idiopathic or presumed idiopathic seizures were recorded in 23 cats after neurological and other laboratory diagnostic testing (including routine tests for infectious and other disorders such as liver, thyroid, and ocular disorders, CSF tap, blood pressure, thoracic radiography and abdominal ultrasound) failed to identify a cause. Some cats also had CT or MRI procedures. The current study also identified reactive seizures from metabolic and toxicant-induced diseases in 20 of the 91 cats studied. These cats had hepatic encephalopathy, insulin overdose, hyperthyroidism, hypocalcemia, polycythemia vera, uremia, and permethrin and organophosphate intoxication. Neurologic examination of these cats did not reveal signs of structural brain disease. For the 3 cats with the cardiac syncope that resembled seizures, all had cardiac conduction disturbances. Whether these were true seizures or the effects of cardiac syncope is difficult to distinguish , even in humans.

In this study, half of the cats with seizures had symptomatic epilepsy, whereas reactive seizures and idiopathic seizures were much less common. Other researchers have suggested that intracranial disease is by far the most common cause of seizures in cats, accounting for up to 87% of seizures. To those researchers, seizures of unknown origin represent symptomatic or probable symptomatic (cryptogenic) epilepsy on the basis of results of MRI or CSF analysis but without any histopathologic confirmation.

Seizure etiology was symptomatic or reactive in most cats, but underlying disease was not associated with seizure type. Status epilepticus was negatively associated with survival time and was more common in cats with symptomatic and reactive seizures. This study also suggested that many cats with idiopathic seizures had a better prognosis than cats with intracranial disease or associated metabolic disease. Cats with idiopathic seizures lived longer than cats with reactive or symptomatic seizures but were also younger.