Seizures in cats are a frequently diagnosed neurologic condition and a major reason for referral to veterinary neurologists. Some animals with seizures may be well controlled with simple medication protocols, while others may have serious or life threatening disease. Once thought to be causes almost exclusively by structural disease, cats are increasingly diagnosed with idiopathic epilepsy as an underlying cause of seizures. Seizures in animals less than a year of age (juvenile onset seizures) may have different causes and prognoses than in adults due to an incompletely developed brain.
The purpose of this paper was to describe a series of cats with juvenile onset seizures, including their etiologies and long term prognosis.
Medical records from a veterinary teaching hospital were evaluated for cats presenting with a history of seizures at less than 1y of age. Cats were required to have a complete medical record, definitive clinical signs of a seizure, and a full diagnostic workup. Signalment, age at seizure onset, type of seizure (focal or generalized, tonic, clonic, or tonic-clonic), presence of cluster seizures or status epilepticus, initial treatment, outcome, and cause of death (if applicable).
Cats with toxic or metabolic disease were not classified as having epilepsy, but rather reactive seizures. International Veterinary Epilepsy Task Force criteria were used to classify cats as having idiopathic epilepsy if there were >2 seizures prior to diagnosis, normal serum biochemistry and CBC, a normal MRI and CSF analysis, and serum bile acids <28mol/L.
Fifteen cats met inclusion criteria for the study: 9 DSH, 2 DLH, and one each of Tonkinese, Ragdoll, and Abyssinian. 8 were MN, 3 FS, 2 MI and 2 FI. Median age of initial evaluation was 30 weeks with seizure onset at 27 weeks. 60% of cats had generalized seizures alone, and 20% had focal seizures alone. The remaining 20% had a combination of focal and generalized seizures. 40% of cats had cluster seizures, and 13% status epilepticus.
After workup, 47% of cats had structural epilepsy and 26% idiopathic epilepsy, with the remaining 26% having reactive seizures.
All 7 cats with structural epilepsy had inter-ictal neurologic abnormalities including ataxia (5 cats); menace response deficits (4 cats); postural deficits (6 cats); anisocoria (2 cats); and opisthotonus (2 cats). 6 cats had generalized seizures and 1 cat both focal and generalized. Ultimate diagnoses were FIP (2); head trauma (2); porencephaly (1); occipital arachnoid diverticula (1); and non-infectious meningioencephalitis (1). Cats with FIP and encephalitis were euthanized, the remainder were alive at 1year post diagnosis.
Cats with idiopathic epilepsy had a normal inter-ictal exam, with the exception of one cat with mild obtundation (which may have been a post ictal phenomenon). One year survival in this group was 100%. One at had focal seizures one generalized, and two had both focal and generalized.
All cats alive at the time of publication had good seizure control. All cats were on phenobarbital; one was also receiving levetiracetam, and one also received potassium bromide and zonisamide.
All 4 cats with reactive seizures were ultimately diagnosed with portosystemic shunts based on elevated bile acids and abdominal ultrasonography or CT angiography. Ameroid constrictors were placed in two cats, declined in one, and the fourth had multiple shunts not conducive to ameroid placement. One cat was alive at 1year post discharge and one was lost to follow up with the remaining having died. No anti-epileptic drugs were used in any cat.
The findings of this paper suggest that structural epilepsy is the most common cause of multiple seizures in cats less than 1 year of age. Cats with structural epilepsy are likely to have an abnormal neurologic exam, while cats with idiopathic epilepsy are less likely to. While no statistical trend was found between seizure semiology and cause of epilepsy, more of the cats with idiopathic epilepsy had focal seizures than those with structural epilepsy.
There were several limitations to this study. One of them was the small sample size, collected over a significant period of time. The use of cats presenting to a tertiary care institution may also have biased the data, as many cats with reactive seizures (ie due to hypoglycemia or intoxication) would likely be diagnosed at the primary care veterinarian and not reach a referral center. This may have significantly biased results.
While further work is needed to determine the causes, prognosis, and ideal treatment for juvenile onset epilepsy in cats, this paper provides some information on seizures in young cats and provides a foundation for further investigation. (MRK)