Feline audiogenic reflex seizures (FARS)
Myoclonic seizures are an involuntary jerk of the legs and/or body that can be likened in appearance to a brief electric shock. In FARS, these sorts of seizures can be triggered by noise. Seizures induced by noise are known as reflex seizures. Therefore the term FARS has come about because we see cats that develop seizures in response to noise. Mark Lowrie, veterinary neurologist at Movement Referrals, is responsible for discovering and reporting the best management for cats with this condition.
What is FARS?
This degenerative syndrome has been called feline audiogenic reflex seizures (FARS); with ‘reflex’ referring to the fact that the seizures are brought on by a stimulus and ‘audiogenic’ referring to the fact that this stimulus is a sound.
What causes FARS?
The cause of FARS remains unknown but it is surprising to see it affects a large number of aged cats of many different breeds.
What are the signs of FARS?
FARS seems to occur exclusively when cats are 10 years or older, with some cats being as old as 19 when the seizures are first seen. Although any breed of cat can be affected, one third of affected are Birmans. Many cats had heart or kidney problems amongst other long-term conditions. However, these conditions are commonly seen in older cats and enough cats were found that had noise-induced seizures with no heart or kidney problems to suggest that this is not a cause for noise-induced seizures in cats.
The noises provoking these seizures tend to be high-pitched, relatively quiet sounds, e.g. computer keyboard tapping or mouse clicking; paper or plastic bags crinkling; the sound of cutlery on a ceramic plate when eating or preparing food; foil crinkling; and the clinking of keys. There have even been some more unusual triggers such as walking on a wooden floor with bare feet or squeaky shoes; the short sharp scream of a young child; and even the sound created by a dog scratching her neck and jangling her collar.
If the volume of the sound increases this has been found to increase the severity of the seizures. If the sound is persistent then this can cause repeated jerks (myoclonic seizures) of the body culminating in a full generalised tonic-clonic seizure (GTCS).
The descriptions of the different types of seizures seen in FARS are given below:
- Generalised tonic-clonic seizures – the seizure begins with contraction of all skeletal muscles and loss of consciousness. The cat will usually fall to the side with the legs stretched out and the head back. This is the tonic portion of the seizure. Sometimes the cat may vocalise or have facial twitching. Vocalisations are involuntary and do not indicate pain. Often the cat will drool excessively, urinate, or defecate. The tonic portion of the seizure is usually very brief and gives way to the clonic phase of the seizure. Once the clonic phase begins the cat will have rhythmic movements. Typically this consists of clamping the jaws and jerking or running movements of the legs.
- Myoclonic seizures – The second type of seizure that was reported were the myoclonic seizures. They often only last for a fraction of a second, and many cats will appear as if they remain conscious during this time as the episodes are so brief (see video). This seizure type is seen in almost 95% of the cats reported with FARS.
- Absence seizures – Finally, the third type of seizure is called an absence seizure, although it is sometimes referred to as a petit mal seizure. This is when a cat loses awareness of their surroundings for up to 20 seconds. The cat will seem to stare vacantly into space and not respond to their name being called. These were less commonly seen in this study, being observed in only six cats. However, these are easy to miss and so we cannot rule-out that they are more common than what we have reported here.
At least half of cats with FARS have some form of hearing difficulties or may be completely deaf. This is a surprising finding as it would have been thought that deafness would cure a noise-induced problem! However, there are potentially two reasons for this. Firstly, cats have an ultrasonic hearing range, allowing them to catch mice that communicate with each other in this ultrasonic frequency range. Many of the domestic noises found to precipitate seizures have a high component of ultrasonic frequencies. Therefore they may sound innocuous to us but to cats sensitive to these frequencies they actually sound more startling. Secondly, deafness in cats seems to affect their ability to hear lower frequencies but usually their ability to hear this ultrasonic range is unaffected.
How do I diagnose FARS?
Unfortunately, the diagnosis of FARS cannot be based solely on the signs shown by a patient. Other neurological conditions such as brain cancers, and bleeding into the brain can potentially cause similar signs. Further tests are always required.
This should start with comprehensive blood work to rule-out many of the conditions that can cause seizures in older cats. If these results are normal then special imaging studies such as MRI scans can help your vet to make a diagnosis. Collection of fluid from around the brain (cerebrospinal fluid analysis) is also an important test to perform if it can be performed safely.
Can FARS be treated?
This condition will worsen over time regardless of treatment. However, an antiepileptic medication called levetiracetam seems very effective at controlling the myoclonic and generalised tonic-clonic seizures in cats. If the GTCS remain poorly controlled then phenobarbital can be added. Another key feature of levetiracetam is that when it has been used to manage the seizures associated with FARS, owners report that their cats became brighter and seemed to develop a whole new lease of life. Therefore management with levetiracetam is recommended even if signs are relatively mild.
What is the prognosis for FARS?
Cats that had suffered from these seizures for more than two years (approximately half of the cats in our study) started to show a gradual decline in their health in that they became weak and wobbly in their legs, less responsive, had stopped jumping, lost weight, started soiling in the house and got stuck in corners. This suggests the disease is a slowly progressive degenerative condition and although we have not yet found the cause, we are working hard to try and find the gene or genes responsible for this syndrome.