Hypnic Headache: A Rare Primary Headache Syndrome in an Indian Population with a Mini Review of Literature

Context: Hypnic headache (HH) is a rare primary headache syndrome first described by Raskin in 1988. Aim: To describe the occurrence of HH in Indian patients and compare its clinicoepidemiological features to those published in the literature and attempt to trace some of the evolving concepts regarding its etiology and clinical features since it was first described. Materials and Methods: Patients attending the neurology outpatient department of a tertiary referral teaching hospital from 01-05-2011 to 30-04-2016 who were identified to have HH as per ICHD 3 beta criteria were included in the study. A meticulous history of the headache and comorbidities, clinical examination, Epworth Sleepiness Scale, blood counts, blood biochemistry, magnetic resonance imaging (MRI) scans of the brain and polysomnography (in selected patients) were done and the results were compared to selected international literature. Results: A total of 11 patients with HH were identified during the study period, of which 8 (72.72%) were males and 3 (27.27%) were females. The age of the patients varied from a minimum of 53 years to a maximum of 78 years (Mean: 63.36, SD: 8.09).The frequency of attacks per month ranged from 5 to 46(Mean: 20.36, SD: 11.67).The duration of each headache episode ranged from a minimum of 30 minutes to a maximum of 4 hours (Mean: 1.93, SD: 1.23). The occurrence of the headaches was maximum during the time periods of 0.00-2.00am and 2.00-4.00am (38% and 36%, respectively). The pain was dull in a majority of patients, 7 (63.63%). Trigeminal autonomic features such as lacrimation, ptosis, or rhinorrhea were not recorded from our cohort. Motor activity was noted in 7 (63.63%) cases. Two (18.18%) patients had associated migraine headaches whereas 3 (27.27%) had associated tension-type headaches. None of the patients in our series had chronic obstructive pulmonary disease. Four (36.36%) patients had systemic hypertension and 1 patient (9.09%) had diabetes mellitus. Two (18.18%) patients had symptoms of obstructive sleep apnea syndrome. Three (27.27%) patients had symptoms of excessive daytime sleepiness according to the Epworth Sleepiness Scale. Blood examinations and MRI were normal in all patients, except for the findings of a few lacunar infarcts and nonspecific T2 weighted hyperintensities in 3 patients (27.27%). Conclusion: Our study proves the existence of the newly described primary headache syndrome called HH in the Indian population. On comparing our results with the international literature, the similarities are much greater than the differences. MRI voxel-based morphometry to demonstrate the loss of gray matter in the posterior hypothalamus may prove to be a reliable test to diagnose primary HH in the future.