Clinical considerations on side-locked unilaterality in long-lasting primary headaches.

The relevance of side-locked unilateral pain (with no side shift) in diagnosing and differentiating primary long-lasting cephalgias such as tension headache and migraine is not clear. In the present study we have retrospectively examined the frequency of side-locked unilaterality in 1169 primary headache outpatients, whose pain duration was more than four hours. The cases were migraine (66%), tension-type headache (21%) and non-classifiable headache and atypical facial pain (not well defined headaches) (13%). The occurrence of side-locked unilateral pain was more frequent in migraine (17%) than tension headache (4%). However side-locked pain was found to be more frequent in patients with not-well-defined head pain (28%). Of the 1169 patients, 181 (15%) had side-locked unilateral pain: 70% of the 181 had migraine, 25% were not-well-defined head pain cases and 5% were tension-type headache cases. The high percentage of migraine cases in the side-locked unilateral group reflects the high proportion of migraine patients in the studied population.