Oligohydrosis and hyperthermia: pilot study of a novel topiramate adverse effect

A 6-year-old boy with partial complex seizures developed recurrent episodes of hyperthermia 2 months after topiramate was introduced into his antiepilepsy drug regimen. Further investigation revealed that the febrile episodes were related to environmental temperature and physical activity. A pilocarpine iontophoresis sweat test showed that the amount of sweat produced by the child was 5% that of age-matched controls. Topiramate discontinuation resulted in the disappearance of febrile episodes and normalization of sweat quantity in repeat sweat testing. Based on this observation and the previous data on zonisamide and isolated case reports on topiramate-related hyperthermia and the effect on sweat production, topiramate was suspected of causing oligohydrosis. A pilot study was carried out involving 13 additional children and young adults (age range 1-37 years) receiving topiramate. All patients were directly questioned regarding symptoms of decreased sweating and heat intolerance, went through a pilocarpine iontophoresis sweat test, and were compared with 14 age-matched controls who went through the sweat test for unrelated reasons. Nine of the patients were found to have reduced sweat quantity on the pilocarpine iontophoresis sweat test (including index case) (mean 0.089 g/30 minutes, SD 0.082; age-matched control: mean 0.21 g/30 minutes, SD 0.06). Eight of them were children (below 16 years). However, only three patients revealed symptoms related to heat intolerance. Topiramate is most likely responsible for decreased sweat production as detected by a pilocarpine iontophoresis sweat test. The effect seems to be more significant in children than in adults. There is a discrepancy between test results and clinical symptoms. Interestingly, oligohydrosis was found to be a relatively common side effect of zonisamide. Both zonisamide and topiramate share a carbonic anhydrase inhibitor activity. The significance of oligohydrosis in hot climates should not be underestimated. Its extent, the role of sweat test prediction, and clinical significance during topiramate treatment should be further estimated.