How to diagnose cluster headache
Like all primary headache syndromes, the diagnosis of cluster headache is made clinically based on the patient’s history according to Third edition of the International Classification of Headache Disorders (ICHD-3). The ICHD-3 criteria require at least 5 attacks that are strictly unilateral, severe or very severe, orbital, supraorbital or temporal pain lasting for 15-180 minutes, when untreated. The signature feature of cluster headaches is the association with cranial autonomic symptoms. The ICHD-3 criteria require at least one of the following to be present, ipsilateral to the pain side: conjunctival injection, lacrimation, nasal congestion, rhinorrhoea, eyelid oedema, forehead and facial sweating, miosis or ptosis. Patients with cluster headache are usually restlessness or agitated during attacks. In the rare cases in whom cranial autonomic symptoms are absent, the presence of restless or agitation is sufficient to make the diagnosis. The attacks occur at a frequency that ranges between one every other day and 8 per day.
Attacks occur in series lasting for weeks or months (so-called cluster periods or bouts) separated by remission periods usually lasting months or years. Cluster headache is further subclassified depending on the duration of the cluster bout. Approximately 10-15% of patients have chronic cluster headache, without such remission periods or remission periods lasting less than 3 months per year. The remaining 85-90% have episodic cluster headaches with remission periods lasting more than 3 months per year.
Diagnosis can be aided by observation of an attack or photograph or video of an attack demonstrating cranial autonomic symptoms. Between attacks neurological examination is usually normal though some patients can have a partial Horner’s syndrome.
The main differential diagnoses of cluster headache are paroxysmal hemicrania and secondary causes. Paroxysmal hemicrania is phenotypically similar to cluster headache but the attacks are shorter lasting 2-30 minutes, usually occur more than five times daily and responds exquisitely to indomethacin. A trial of indomethacin should be considered in patients with probable cluster headache if attacks are shorter than 30 minutes or occur more than five times daily.
Rarely a patient can present with a clinical syndrome resembling primary cluster headache due to secondary pathology. This may include pituitary tumour, cavernous sinus pathology, arterial dissection or aneurysm. Magnetic resonance imaging (MRI) is required to exclude secondary causes in all patients who present during the first bout. In those presenting in the second bout or later a secondary cause is extremely unlikely, and risk of incidental findings is not insignificant, but it is reasonable to perform imaging as the devastatingly disabling attacks frequently provoke concern about secondary causes and imaging is often reassuring.
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The IHS Cluster Headache Awareness Campaign focuses on educating Healthcare Professionals, offering the essential information to assist them in managing patients with cluster headache.
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