Successful treatment with levothyroxine for idiopathic hypersomnia patients with subclinical hypothyroidism

Our objective was to discuss the effect of levothyroxine on excessive daytime sleepiness (EDS) and a prolonged nocturnal sleep at patients with idiopathic hypersomnia who presented with subclinical hypothyroidism.

We present two patients with hypersomnia who complained of EDS and a prolonged nocturnal sleep time. Sleep architecture and subjective daytime sleepiness were estimated by polysomnography (PSG) and Epworth Sleepiness Scale (ESS), respectively. Diagnoses were made using the International Classification of Sleep Disorders, 2nd Edition criteria for idiopathic hypersomnia with long sleep time.

PSG demonstrated a short sleep latency, a prolonged total sleep time and normal proportions of all non-rapid eye movement (REM) and REM sleep stages. Nocturnal PSG excluded other causes of EDS. No medical, neurological and mental disorders were present. Their laboratory data indicated mildly elevated thyrotropin, despite free thyroxine (T4) and triiodothyronine (T3) estimates within their reference ranges, which is a characteristic of latent hypothyroidism. Levothyroxine (25 microg/day) was administrated orally. After treatment with levothyroxine for 8 weeks, the mean daily sleep times decreased. EDS was also improved, and a significant decrease in the ESS score was observed. Levothyroxine was effective for their hypersomnia and well tolerated.

It should be noted that hypersomnia may be associated with subclinical hypothyroidism, although few abnormalities in physical and neurological examinations are present.