Journal Scan: High-frequency sounds can lead to seizures in some older cats
Why they did it
Researchers in the United Kingdom, aware of the occurrence of seizures induced in cats exposed to sounds at certain frequencies, sought to characterize feline audiogenic reflex seizures (FARS) in order to provide veterinarians a description of this previously unreported syndrome.
What they did it
Cases of suspected FARS were solicited from primary veterinarians and owners through print media, the Internet and the radio. Cat pedigrees, medical histories and cheek swab DNA samples were collected. A detailed online questionnaire was made available to those owners whose cats met the inclusion criteria after an email or a telephone interview. A full medical history and, in many cases, video recordings of episodes were also reviewed.
The questionnaire contained several sections collecting information on signalment, precipitating factors, the cat’s overall health and any relevant therapies or medications. It also asked for detailed descriptions of the episodes. The questionnaire was designed to avoid leading owners to make conclusions or to provide “expected answers.”
For inclusion in the study, the cats had to have suffered three or more generalized tonic-clonic seizures (GTCSs) precipitated by the same sound and lasting less than five minutes for a minimum one-year history. Other types of episodes such as myoclonic seizures or jerks and absence seizures were described separately on the questionnaire. A total of 96 cats met the criteria and were included in the study.
What they found
The mean age for seizure onset in this cohort was 15, with a fairly even distribution of males and females. Many breeds were represented, but Birman cats were most common (n=30). The noise stimulus for all cats was high-pitched, and audiogenic kindling—repeated sound stimulation resulting in progression from myoclonic seizures to GTCS—was observed in most of the subjects. The seizure episodes occurred an average of once every three to six months, and of the cats in which diagnostics were pursued, no cause for the seizures was found.
Some of the more common sounds that induced FARS episodes in affected cats were
- Crinkling tin foil (n=82)
- Dropping a metal spoon into a ceramic bowl (n=79)
- Clinking or tapping a glass (n=72)
- Crinkling paper or plastic bags (n=71)
- Typing on a computer keyboard or clicking a mouse (n=61)
Many of the cats had concurrent disease, the most common being chronic renal disease and hyperthyroidism. None of the cats included in the study demonstrated progression of the seizure disorder. Interestingly, 50% of the cats were described as having hearing loss or deafness. Forty-four cats received antiseizure medication—phenobarbital or levetiracetam—to control their seizures, but only levetiracetam resulted in good control of both the myoclonic seizures and GTCSs.
FARS is newly defined nonprogressive clinical syndrome affecting geriatric cats characterized by myoclonic seizures and GTCSs triggered by high-pitched sounds, often with persistence of the sound serving to increase the severity of the seizure episode. Levetiracetam appears to be more effective than phenobarbital in controlling both the myoclonic seizures and GTCSs associated with FARS. Birman cats were overrepresented in this study, suggesting a breed predilection and genetic basis for the disorder. Hearing loss or deafness reported in many of these cats may not indicate damage to the area of the cochlea associated with higher frequency hearing, providing an explanation for how FARS occurs in cats with apparent hearing impairment or deafness.
Lowrie M, Bessant C, Harey RJ, et al. Audiogenic reflex seizures in cats. J Feline Med Surg 2015;epub ahead of print.
Link to abstract: http://www.ncbi.nlm.nih.gov/pubmed/25916687