Lifetime prevalence and concordance risk of cluster headache in the Swedish twin population

Objective: To examine the lifetime prevalence and the concordance risk of cluster headache (CH) in a twin sample representative of the Swedish general population. Methods: The authors assessed CH as defined by the second edition of the International Classification of Headache Disorders in 31,750 registered twins born from 1935 to 1958. Structured lay screening interviews were followed by neurologist interviews of possible cases. Co-twins of affected index twins were follow-up interviewed regardless of their screening outcome. Results: A total of 250 screening-positives (0.8%) were found, of which 218 (88%) were follow-up interviewed. Forty-five (21%) had the CH diagnosis verified. Among screen-negatives, hospitalization records pointed at two more verified cases and index twins at one more verified case. A total of 48 CH cases provided a crude lifetime prevalence of 151 per 100,000 (95% CI: 108, 194). The male-to-female sex ratio corresponded to 4.8 (95% CI: 2.3, 9.9). The crude lifetime prevalence of CH was higher in the twins born from 1945 to 1958 than in the twins born from 1935 to 1944 (190 vs 90/100,000). CH recurred in 2 of 12 co-twins of monozygous index twins (including 1 nonparticipant twin), whereas all co-twins of 25 dizygous index twins proved to be unaffected. Conclusion: As many as 1 per 500 of the general population are affected by cluster headache. Twin concordance seems low, but genetic factors may play a role for familial clustering.