Feline Audiogenic Reflex Seizures (FARS), as the authors of a recent paper have named the condition, manifest as involuntary muscle activity (myoclonic seizures) starting at 10 years of age or older, which high frequency sound triggers.
The study, published in the Journal of Feline Medicine and Surgery, centers on data gathered from owners of 96 cats who had three or more generalized tonic-clonic seizures linked to a specific sound such as crinkling aluminum foil or tapping a spoon against a ceramic bowl or glass.
And, while most of the affected cats were domestic shorthairs, a significant number (31%) were Birmans or Birman crosses.
Seizure and Epilepsy Terminology for Understanding This Study
In order to interpret the results of the study, it is important to explain more about seizures in general, epilepsy and the different types of seizures seen in the cats in the study.
Epilepsy is a brain disorder leading to repeated seizures. Brain injury, strokes, metabolic disorders, tumors and any other illness that damages brain tissues may result in epilepsy. In some cases a cause for the onset of epilepsy can’t be determined, although there is increasing evidence for a genetic basis in certain situations.
Experts define seizures, also called convulsions, as uncontrolled electrical activity in the brain. There are many types of seizures:
- Absence (or petit mal) means a brief loss of consciousness which often goes unnoticed, as the animal may simply appear to be staring into space.
- Monoclonic involves involuntary muscle jerking or twitching either whole body or specific parts.
- Generalized tonic-clonic (or grand mal) results in whole body convulsions alternating with rigidity, and loss of consciousness.
- Reflex means a specific trigger such as light or sound initiates the seizure. Light, particularly strobes or fluorescent lights flickering at a specific rate, are common triggers in humans
- Audiogenic are reflex seizures triggered by a specific sound.
Other Health Issues in FARS Study Cats
Several things make interpreting the FARS data difficult. FARS occurs in older cats, and the cats in the study had other age-related health conditions with the potential to trigger seizures.
Liver or kidney degeneration, hypoglycemia and hyperthyroidism can all result in increased likelihood of seizures, as can toxins, including those found in flea collars. Older cats are often more sensitive to these toxins.
In this study, 40% of the cats had concurrent medical conditions, chronic renal disease being most common. Interestingly, the presence of these health issues did not result in the FARS seizure activity becoming worse and treatment helped in some cases. This suggests that these medical conditions were not the underlying cause for the seizures.
More intriguing was the finding that 50% of the cats had some level of hearing impairment and five owners reported their cats as completely deaf. This would seem inconsistent with the sound-related seizures the cats experienced but there are several potential explanations.
Deafness in cats is often linked to damage in the areas of the ear where lower range sounds (7600Hz) are heard. Higher frequency sound ranges may not be affected. Only 16 of the 48 cats with reported hearing loss had further specialized testing– CT scans (4) or MRIs (12)– and none of those tests revealed a cause for the apparent deafness.
Given the number of Birmans who developed the condition, scientists must further examine the role of inheritance, especially in the light of genetic links to certain types of deafness seen in dogs and rodents that are linked to audiogenic seizures similar to those reported in the study.
Fate of the Cats in the Study
Twenty-two of the cats were euthanized within two years of developing the condition but owners reported slow decline in health, weakness and incoordination in the hind limbs, weight loss and behavioral changes such as toileting in inappropriate areas and getting stuck in corners as reasons for euthanasia. How much the seizure activity contributed to the overall decline is not clear from this study.
Questions Remain Unanswered About FARS
The study has raised more questions than it answered. For example, experts need to pursue the following questions to further understand the condition.
- Is this truly a new syndrome or has the condition simply not been described before?
- How much of this condition is simply age-related as cats are living longer as result of better care and more old-age syndromes may appear?
- Does hearing loss resulting in only being able to hear high ranges play a role?
- How is FARS related to similar seizures in dogs and rats where a genetic component has been identified?
There is one question that can be answered with a significant degree of certainty.
What Does This Mean For Cat Owners?
The first part of the answer to this question is levetiracetam – this drug has few significant adverse side effects, and likely manages late onset seizures in elderly cats well. Thus, even if a cat develops the condition, management is possible.
The second part is that this newly reported condition occurs late in cats’ lives, so diagnosing FARS is not likely to result in significant changes in the life of the individual cat. For owners on limited budgets there is no need to invest in expensive testing.
One further area of consideration based on this study involves the Birman cat. Owners of this breed may be able to contribute to the understanding of this condition as it specifically relates to this breed.