A population study of the incidence of fibromyalgia among women aged 26-55 yr.

In a population survey, we assessed the incidence of fibromyalgia (FM) among females. A screening questionnaire about pain was distributed twice (in 1990 and 1995) to 2498 females aged 20-49 yr, living in South Norway. A positive answer classified the responder as positive, merely negative answers as negative. One hundred females converting from negative to positive responders and 100 females remaining negative responders (controls) underwent a structural interview and examination for tender points (TP). Of the 870 negative responders in 1990, 717 answered the questionnaire in 1995. Of these, 523 were still negative responders, while 194 were positive converters. Twelve of the converters developed FM and none of the controls. The calculated annual incidence of FM in females was 583/100,000. This rather high incidence is most likely explained by the design of the study, also detecting cases usually not seen in hospital settings.