Temporal lobe epilepsy (TLE) is a newly emerging term in feline seizure discussions and one worth becoming acquainted with. TLE is not an etiology, but rather a specific seizure phenotype (appearance) caused by epileptic seizures in a specific part of the brain (hippocampus) resulting from multitudes of causes.
What does TLE look like?
Cats with TLE have 6 specific stages or appearances. Not all cats go through all 6 stages, nor are all 6 stages apparent. The stages are:
Stage 1: looking around, sniffing, attention
Stage 2: Immobility and staring (arrest)
Stage 3:Orofacial automatism (lip smacking, facial twitching, swallowing, blinking) hypersalivation, mydraisis
Stage 4: Masticatory movement, facial twitching
Stage 5: Head turning, head nodding
Stage 6: Generalized convulsive tonic-clonic seizure
Most cats are observed in stage 2 or 3, and may progress to stage 4 and 5 but stage 6 is rarely observed.
What causes TLE?
Because TLE is not an etiology, but a description of a seizure syndrome located in one part of the brain, any cause of non-TLE seizures can cause TLE seizures as well. This list could include vascular causes, neoplasia, meningoencephalitis (infectious or non-infectious), or idiopathic.
How is TLE diagnosed?
When orofacial automatisms are observed, TLE should be suspected. To confirm TLE, an MRI with changes in the hippocampus is needed. There may be evidence of the seizure etiology such as neoplasia, or vascular disease as well, but the hippocampus must show specific MRI changes. Histopathology can reveal hippocampal sclerosis or necrosis. Some authors think sclerosis precedes necrosis but this sequence isn’t fully established. I won’t bore you with the detailed differences between sclerosis and necrosis, especially since the difference is detected on necropsy.
Can we treat TLE?
Yes! Treat seizures with antiepileptic drugs (AED) as you would any feline or canine seizure disorder. Any 1 seizure more than every 3 months, or longer than 3 minutes warrants a discussion of starting AEDs. Recently, hippocampectomy (removal of part of the hippocampus) has bene published in a cat as a treatment for TLE. This is a well-established treatment for human TLE (a common form of AED-resistant epilepsy in humans) and it carries an extremely high success rate for seizure elimination. Unfortunately, the procedure in cats needs a bit more work before we start considering it standard treatment. The hippocampus is the memory storehouse therefore loss of the hippocampus can cause difficulty with motivation, spatial memory, and learned behavior. Some researchers have described the effect to be similar to feline cognitive disorder in geriatric cats. Hippocampectomy was extensively performed in the 1960s during the time of rapid, although sometimes perhaps unethical, knowledge acquisition of how the brain works in animals and humans. We must acknowledge this work, even if we might find it ethically repulsive today.
Key Points
· Temporal lobe epilepsy is a syndrome, resulting in damage to the hippocampus and a classic seizure presentation.
· Temporal lobe epilepsy can be treated, but may be progressive and unresponsive to treatment once the necrosis stage has been reached. How do we know we reached this stage? No one knows antemortem….stay tuned!
· Cats should take phenobarbital or levetiracetam. These are currently (2023) the only two drugs with enough literature to support their use and predict a reasonable efficacy. (Sorry my zonisamide-using friends.)