Cluster headache is a primary headache disorder characterised by attacks of strictly unilateral severe pain lasting 15–180 min, associated with prominent parasympathetic features. Most patients with chronic cluster headache attending tertiary headache centres have severe functional impairment and emotional distress. 1 Donnet A Lanteri-Minet L Guegan-Massardier E et al. Chronic cluster headache: a french descriptive study.

J Neurol Neurosurg Psychiatr. 2007; 78: 1354-1358

A substantial number of patients with chronic cluster headache continue to have at least three severe attacks per week despite adequate treatment trials, and are therefore diagnosed with medically intractable (or refractory) chronic cluster headache. 2 Mitsikostas D Edvinsson L Jensen R et al. Refractory chronic cluster headache: a consensus statement on clinical definition from the European Headache Federation.

J Headache Pain. 2014; 15: 79

Medically intractable chronic cluster headache is one of the most painful conditions in humans, often referred to as the suicidal headache. 3 Ji Lee M Cho SJ Wook Park J et al. Increased suicidality in patients with cluster headache.

Cephalalgia. 2019; 39: 1249-1256