Tooth brushing can induce seizures in people with epilepsy, a new case study of three people with the condition has found.
"Brushing your teeth is very rhythmic. Our idea is that it causes a rhythmic over-activity in the brain, which feeds back on itself - similar to the effect of strobe lighting on people with photosensitive epilepsy," says neurologist Wendyl D'Souza of St Vincent's Hospital in Melbourne, Australia, one of the team reporting the cases.
Epilepsy occurs when nerve cells in an area of the brain fire more rapidly than usual and in synchrony with one another. This causes seizures that range from "grand mal" seizures - the old term for extreme convulsions and loss of consciousness - to short bouts of staring that may wrongly be blamed on lack of concentration.
Seizures bought on by a benign stimulus such as tooth brushing, reading or strobe lighting - called "reflex" seizures - are rare, D'Souza notes.
Each of the patients in the new study had been diagnosed with epilepsy, and had suffered full-blown convulsive seizures. The tooth-brushing seizures were smaller and included jerking of the mouth, eyes, and face; tongue cramping; and excessive salivation, lasting for up to 90 seconds.
One patient, a 31-year-old woman, who developed epilepsy when 9 years old, was also unable to let go of her toothbrush once the seizure had started. A 33-year-old male patient found that brushing his right lower teeth was most likely to induce a seizure, and that eating potato chips could have the same effect.
MRI scans of all three patients showed physical abnormalities in regions of the brain cortex close to those responsible for processing sensory information from the hand and the face.
According to D'Souza, the abnormalities are responsible both for the smaller tooth-brushing-induced seizures, as well as full-blown convulsive seizures. The full-blown seizures would occur when the abnormal activity spread to other areas of the brain in an "electrical storm", he says.
One of the three patients, a 42-year-old man, recovered completely from his epilepsy after having the abnormality in his brain cortex surgically removed.
The new study brings the number of cases linking tooth-brushing and epilepsy reported in the literature to five. Four of those patients said similar unusual sensations preceded a seizure: numbness in the head or a tingling in the tongue.
Between 3% and 4% of people will suffer from epilepsy at some stage of their life. It is most common in children and older people.
Journal reference: Neurology (vol 68, p 769)
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