Migraine and Cluster Headache – Mechanism and Diagnosis
The commonest form of vascular headache is migraine (megrim means hemicranial). Migraine is characterized by episodic, throbbing hemicranial headache, beginning in childhood, adolescence or early adult life and which tends to decrease in intensity and frequency as age advances. It is estimated that 5% of the population suffers from migraines. Women are slightly more affected. In many cases a positive family history is common.
Mechanism of migraine: Though the exact mechanism is unknown, it is the consensus that an attack of a migraine consists of a neurovascular disorder of the intracranial as well as the extracranial vessels. Sequential studies of cerebral blood flow show an initial reduction which may be localized or generalized followed by increase in blood flow (35-50%) later. The basic cause of this circulatory disturbance is not known. It is found that the blood levels of histamine, serotonin and norepinephrine increase during the attacks. There is also increase during the attacks. There is also increase in platelet aggregation. This may account for strokes which sometimes complicate migraine. The headache has been attributed to excessive pulsation of extracranial arteries, and possibly intracranial ones also.
Classic or neurologic migraine: Here, the episode begins with prominent neurologic symptoms such as visual disturbances (e.g. dazzling zig-zag lines, spreading scotoma, homonumous hemianopia, field defects or rarely total blindness) sensory disturbances affecting one half of the body, disturbances of speech or hemiparesis. There neurologic symptoms last for 15-30 minutes and usually merge into a hemicranial or generalized throbbing headache with nausea and vomiting, all of which may last even for 1 to 2 days. In the majority of cases the duration is much shorter.
Common migraine: Here, there is no preceding neurological symptoms, but there is unheralded onset of headaches, nausea and vomiting following the same sequence. Diagnosis of both classic and common migraine is made mainly from history. Long duration of illness, onset during childhood, positive family history and relief with ergot derivatives are in favor of migraine. Migraine has to be differentiated from other organic disorders such as raised intra-cranial tension, subarachnoid hemorrhage and arteriovenous malformations.
Cluster headache: Another type of vascular headache is a migraine variant known as ‘cluster headache’ (histamine headache, Horton’s syndrome). Men are more affected than women in the ratio 4:1. The headache starts within 3 hours of falling asleep, it is non-throbbing, unilateral, and orbital in location. Along with pain there may be lacrimation, nasal obstruction, rhinorrhea, and sometimes miosis, ptosis, and flushing and edema of cheek-all lasting approximately for an hour or two. It tends to occur every night for weeks or months followed by complete freedom for years. Such clusters of headache may recur over the years. Periods of headache are brought on by stress, prolonged strain, overwork and emotional disturbances. Alcohol, nitroglycerine or tyramine-containing foods may precipitate the headache.