MELBOURNE, Australia -- The persistent rhythmic motions of tooth brushing appear to have triggered seizures in patients with reflex epilepsy, researchers here reported.
MELBOURNE, Australia, March 8 -- The persistent rhythmic motions of tooth brushing appear to have triggered seizures in patients with reflex epilepsy, researchers here reported.
In two adult men and one woman, tooth brushing appears to have overstimulated the primary somatosensory area of the brain, reported Wendyl D'Souza, M.D., of the University of Melbourne, and colleagues, in the March 6 issue of Neurology.
"In a mechanism similar to photosensitive epilepsy, seizure generation in our three cases may require excitation of a critical mass of an already hyperexcitable area within the somatosensory cortex of the parietal operculum," they wrote.
The patients, a 31-year-old woman, a 33-year-old man, and a 42-year-old man, all turned out to have lesions in the identical region of the brain, resulting in what appears to be a simple reflex epilepsy, the investigators said.
"Unlike the simple reflex epilepsies, complex reflex epilepsies are characterized by involvement of higher cortical processes, stimulus anticipation, and a longer latency from stimulus to seizure onset, e.g., eating epilepsy," they added.
But in the case of their patients with tooth brushing-induced epilepsy, there's evidence that oral somatosensory pathways, rather than higher cortical processes, are involved in transmitting the signals to the cortex that trigger the seizures, and that such seizures should be classified as simple rather than complex reflex seizures, they wrote.
Their first patient was a 31-year-old right handed woman who had had epilepsy since age nine, with early seizures brought on by "startle, crowds, and occasionally stressful situations, causing her mouth to jerk on the left."
She found that seizures would also occur more frequently with vigorous tooth brushing using either hand, causing an ill-defined feeling of numbness in her head. Video EEG monitoring performed between seizures showed focal epileptiform discharges and, EEG capturing during seizures showed rhythmic spike discharges over the right frontocentral region. She was found on MRI to have a large lesion, thought to be benign, in the right perirolandic region.
The 33-year-old man, who was right-handed, developed a peculiar sensation when brushing his teeth. It consisted of tongue tingling and jaw tightening, accompanied by "vigorous" salivation. On some occasions the episodes would progress to right facial twitching. After a seizure he had transient facial weakness on the right side, and trouble speaking. He was found on examination to have right upper motor neuron weakness.
Video EEG monitoring in this patient revealed activity in the 4 to 5 Hz theta range over the left parasagittal and temporal region. An MRI acquired with a specific volumetric epilepsy protocol showed a 6 mm diameter lesion in the postcentral gyrus 1 cm superior to the left sylvian. This lesion was near the primary somatosensory cortex for hand and face, and close to regions of language cortex.
The third patient, a 42-year-old ambidextrous man, had had two generalized tonic-clonic seizures after being awoken by an alarm clock.
A history showed that he had been having minor events over the three previous years.
"Seizures began with an 'odd sensation of cramping' in his tongue and jaw on the left, precipitated by the first mouthful of food or brushing his teeth," Dr. D'Souza and colleagues wrote. "When it occurs with eating, a refractory period follows when he cannot bring on an attack unless he has a break from eating. Events were readily induced by rubbing the outer lower gum posteriorly during tooth brushing."
On examination, the patient had subtle left upper motor neuron facial weakness and "questionable" reduced dexterity of the left hand. Video EEG monitoring captured a seizure when he was chewing a cookie; this seizure consisted of behavioral arrest for less than 30 seconds associated with contraction of the lip, more prominently on the left side, with bilateral mentalis muscle contraction.
EEG conducted after a seizure showed bilateral theta range activity, possibly with right-sided predominance.
On MRI, the patient was found to have a 3 mm by 10 mm subcortical focus of increased T2 hyperintensity in the inferior aspect of right postcentral gyrus; this focus was in an identical position to that of the 33-year-old male patient described above. The seizures were eliminated by surgical resection, during which surgeons noted cortical dysplasia.
"Tooth brushing involves a persistent rhythmic oral sensory stimulus," the investigators wrote. "This may explain how this trigger is more likely to evoke the necessary neuronal synchronization to induce seizures compared to other oral stimuli such as eating. Seizures then propagate to the adjacent motor cortex through a direct transcortical pathway. The ability to induce seizures by brushing either side of the mouth suggests that oral somatosensory inputs have bilateral projections. These afferent inputs have bilateral projections to the insular and frontal opercular cortex in nonhuman primates, an anatomically closely related site to the lesion in our patients."