Hypnic headache

Hypnic headache (HH) is a rare primary headache disorder. Its main clinical features are strict sleep-related headache attacks that awaken patients from sleep. As headache attacks often occur at the same time at night, HH has also been referred to as ‘alarm clock headache’. Currently, 225 cases have been reported in the literature. Patients are generally older than 50 years of age at headache onset, but occurrence in younger patients and even children has been described. More women than man are affected. The headache may be bilateral or unilateral. Some migrainous features, such as nausea or photophobia, or mild cranial autonomic symptoms, such as lacrimation, may accompany HH and create diagnostic uncertainty. While most patients display some motor activity during the headache attacks, the agitation and motor restlessness that is characteristic of cluster headache does not appear. The pathophysiology of HH is still enigmatic. Hypothalamic involvement has been considered on the basis of the circadian rhythmicity, relationship with sleep, and imaging evidence of a decrease in grey matter volume within the posterior hypothalamus. Caffeine, lithium carbonate, and indomethacin may be effective for the prevention of attacks, but randomized, placebo-controlled trials are not yet available.