Hypnic (or alarm clock) headache is an uncommon headache disorder. It primarily occurs in age groups over 50 years and is female predominant [1, 2]. It is typically a nocturnal headache, occurring in sleep and waking the patient up, hence the name “alarm clock headache”. It is commonly bilateral but can be unilateral and usually lasts 2–3 h. It is commonly dull or throbbing in character and does not make the patient restless, unlike in Cluster Headache. Most patients engage in some activity after waking up (eating, drinking, showering, reading etc.) [1]. Some patients report improvement with a cup of coffee [3] (which our patient was unwilling to try due to her concern over possible gastric irritation). Sometimes it can be associated with trigeminal autonomic features such as rhinorrhea, tearing and ptosis [1, 2]. Diagnosis is mainly clinical and underlying causes must be excluded. International Classification of Headache Disorders 3rd Edition (ICHD-3)-beta [5] provides diagnostic criteria for hypnic headache. Clinical trial evidence for treatment is lacking and the usual empiric treatment options include indomethacin, lithium, caffeine and melatonin which is structurally similar to caffeine [1,2,3,4,5,6]. A recent study has suggested that lithium appears to be the most effective treatment option [6]. It was not tried in our patient as her symptoms responded well to the more readily available indomethacin. Indomethacin is noted to be particularly useful if headache is unilateral [1, 2], as in this case. Given its relationship with a variety of headache disorders, indomethacin has been the subject of various studies and reviews. While some headache disorders like hypnic headache, primary stabbing headache, primary cough headache and hemicrania spectrum headaches are responsive to indomethacin, some are resistant. (e.g. Cluster headache). Why indomethacin is better in headache management than other non-steroidal anti-inflammatory drugs remains unclear [7, 8]. A recent case report described improvement of hypnic headache with greater occipital nerve block when all pharmacological options failed [9]. Pathophysiology of hypnic headache is not clearly identified. Currently available evidence suggests involvement of posterior hypothalamus as in Cluster Headache [10]. Our patient fulfilled the ICHD 3-beta criteria for Probable Hypnic Headache. Absence of autonomic features is a required criterion but some patients do report autonomic manifestations [1, 2, 6], as noted in our patient. She did not meet the criteria for related headache disorders like cluster headache and the hemicrania spectrum. Cluster headache usually occurs in younger males, produces excruciating pain with prominent autonomic features and has poor response to indomethacin. Paroxysmal hemicranias do respond to indomethacin but are excruciating and more frequent (more than 5/day as per ICHD-3). Other indomethacin responsive headache disorders like primary cough headache and primary stabbing headache were unlikely in our patient, as the main clinical criteria were not present. Secondary causes of chronic daily headache such as tumours were excluded in our patient with normal MRI imaging. Nocturnal hypertension may cause a similar headache syndrome [11]. Multiple blood pressure measurements were normal in our patient including recordings during episodes of nocturnal headache. The exploding head syndrome is another rare nocturnal disorder seen especially in women over 50 years. However it is rather an auditory sensation than pain and is described as a sudden momentary snap or a pistol shot sound while falling asleep. Our patient had a recurrence of headache after discontinuation of indomethacin, but she has been compliant with medication since then. While most headaches are benign and can be treated easily, some of the rare headache disorders can cause distress to both the patient and the clinician. Difficulties in their diagnosis inevitably leads to extensive investigations and delays in proper treatment. More awareness about the uncommon headache disorders and their management can lead to early initiation of appropriate treatment and significant cost savings.
