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Hypnic headache (HH) is an uncommon primary headache disorder that tends to only affect patients older than 50 years of age. However, single case reports also describe HH also in younger patients and even in children [1]. Patients usually wake up with a holocranial headache on more than 15 nights per month. Usually the headache lasts more than 15 min. As the headache often occurs at the same time at night, this headache entity is also referred to as an 'alarm clock headache'. In addition, HH attacks can also arise from day-time naps. More women than men are affected by this disease. Moderate migraneous features such as nausea or phono- or photo-phobia might accompany the pain, and trigeminal autonomic symptoms such as lacrimation or rhinorrhea are missing in most cases [2]. In contrast to migraineurs, HH patients report that they get out of bed when they awake with headache and perform some motor activity [3]. Some patients take a shower, some eat, some read and some go for a walk. However, HH patients do not present with the kind of restlessness that can be observed in cluster headache patients (Box 1).
The underlying pathophysiology of HH is still mysterious. The circadian rhythmicity of headache attacks is the most striking pathognomonic feature in HH, and it is thought to reflect possible hypothalamic involvement. Initially, some authors suggested HH to be a rapid eye movement (REM) sleep disorder, but previously non-REM (NREM) sleep-associated HH attacks have been also described [4,5]. Other authors have suggested that obstructive sleep apnea or nocturnal high blood pressure might cause HH, but these cases should be rather considered as secondary causes. HH can also occur secondary due to intracranial lesions [6-8] or ischemic stroke in the midrostral upper pons [9].
Controlled clinical trials investigating the efficacy of different treatment options are currently unavailable. One typical feature of HH is that caffeine is often helpful to relieve pain as an acute acting agent and also prevents pain due to its prophylactic properties when consumed at night before going to bed.
A significant connection between headache disorders and caffeine is quite well known. Caffeine-containing mixed analgesics are widely used in several headache disorders and are often effective. Chronic caffeine intake can induce withdrawal...