Hypnic headache.

Hypnic headache is a rare primary headache disorder that is characterized by exclusively sleep-related headache attacks in patients usually beyond 50 years of age. Only 174 cases have been reported in the literature so far. Owing to its low prevalence, clinical features and therapeutic options, as well as underlying pathophysiologic mechanisms, are widely unknown or being controversially discussed. The association of hypnic headache with rapid-eye movement sleep was strongly contradicted in recent articles, while an association with hypothalamic dysfunction is thought to be one important pathophysiological mechanism. Common acute, as well as prophylactic, treatment is caffeine intake, either in the form of a cup of coffee or a caffeine tablet. Lithium, indomethacin and melatonin were promoted as potent medical treatments, while almost every other drug commonly used to treat headache or other pain syndromes was reported to be effective in single case reports on hypnic headache.