Periodic hypersomnia: case report with biochemical and EEG findings.

We report on a 23-year-old patient with periodic hypersomnia. Electroencephalographic (EEG) background activity for this individual was slightly slowed in the EEG during an episode of hypersomnia, and intermittent slow activity was found in addition. Usual laboratory parameters were normal; however, leucine-enkephalin was markedly elevated in the plasma at that time, whereas free cysteine could not be demonstrated. Clinical findings were normal in the following years, and the EEG background activity returned to normal; leucine-enkephalin and cysteine also returned to normal values.