Cluster headache

Cluster headaches are among the most painful conditions known to medicine. They belong to a group of primary headache disorders called trigeminal autonomic cephalalgias (TACs), characterised by severe unilateral head pain combined with ipsilateral autonomic features. They are called "cluster" headaches because the attacks occur in bouts — cluster periods — typically lasting several weeks to months, after which the sufferer enters a remission that can last months or years.

**Who is affected:** Cluster headaches are less common than migraine, affecting an estimated 0.1% of the population. They predominantly affect men (male-to-female ratio approximately 3:1) and typically begin between the ages of 20 and 40.

**Causes:** The exact mechanism is not fully understood, but cluster headaches involve activation of the trigeminal nerve and the sphenopalatine ganglion (a nerve cluster behind the nose), producing severe pain and autonomic changes. The hypothalamus appears to drive the characteristic circadian and circannual periodicity of attacks. Triggers during a cluster period include: - Alcohol - Tobacco - High altitude - Bright or flickering light - Physical exertion - Heat (hot weather or bathing) - Foods containing nitrates - Vasodilating medications

**Symptoms** — a cluster attack typically includes: - Severe, excruciating, drilling or burning pain strictly on one side, centred on or behind the eye - Pain spreading to the forehead, temple, jaw, or neck on the same side - Attacks lasting 15 minutes to 3 hours, occurring 1–8 times per day - Most attacks at night, typically 1–2 hours after sleep onset - Ipsilateral autonomic features: tearing, red or injected eye, nasal congestion or rhinorrhoea, ptosis (drooping eyelid), miosis (constricted pupil), facial flushing or sweating, periorbital oedema - Restlessness and agitation during the attack (unlike migraine, where lying still is preferred)

**Cluster periods** are consistent in their characteristics for a given individual — often occurring seasonally (e.g., every spring or autumn). Most patients have episodic cluster headache, with cluster periods of one week to one year separated by remissions of at least 12 months. Chronic cluster headache (fewer than 30 days of remission per year) affects a minority.

**Treatment** has two components: acute (aborting attacks) and preventive (reducing attack frequency during cluster periods). High-flow oxygen and subcutaneous triptans are the standard acute treatments. Preventive medications include verapamil, corticosteroids, and lithium. When medications are insufficient or poorly tolerated, interventional approaches targeting the sphenopalatine ganglion or occipital nerve offer effective alternatives.