Hemicrania continua (HC) is a primary headache disorder characterised by continuous unilateral head and facial pain with superimposed exacerbations. Although it can mimic migraine, it differs significantly in pathophysiology, clinical features, and management.

Clinical features:

HC presents as a persistent, strictly unilateral moderate pain that waxes and wanes but never completely resolves. Exacerbations are often severe and may be accompanied by migrainous symptoms such as photophobia, phonophobia, nausea, and vomiting.

Cranial autonomic symptoms:

During exacerbations, patients frequently experience ipsilateral autonomic features including conjunctival injection, lacrimation, nasal congestion or rhinorrhoea, ptosis, or miosis. These overlap with trigeminal autonomic cephalalgias but are less prominent than in cluster headache.

Differentiation from migraine:

Unlike migraine, HC is continuous rather than episodic. Migraine attacks last 4-72 hours with pain-free intervals; HC pain is unremitting. Migrainous aura is absent in HC. Response to indomethacin is diagnostic for HC, whereas migraine does not respond consistently.

Pathophysiology:

The exact mechanism remains unclear but likely involves activation of the trigeminal-autonomic reflex and central sensitisation. The indomethacin response suggests involvement of prostaglandin pathways.

Relevance to idiopathic intracranial hypertension (IIH):

IIH can present with headaches mimicking migraine or other primary headaches including HC-like features. However, IIH headaches are typically diffuse and associated with raised intracranial pressure signs (papilloedema). Differentiation requires neuroimaging and lumbar puncture.