RESUMEN
To determine whether the effects of symptom duration on fibromyalgia physical impairment are moderated by symptom self-efficacy, data from 572 female participants, who were members of a large health maintenance organization and had a diagnosis of fibromyalgia syndrome (FMS) were assessed. Age, symptom duration, history of physical, sexual, and emotional abuse, fibromyalgia-specific self-efficacy (Arthritis Self-Efficacy Scale adapted for FMS [ASES]), depression (Centers for Epidemiological Studies Depression Scale [CES-D]), fibromyalgia physical impairment (Fibromyalgia Impact Questionnaire [FIQ]), and pain (McGill Present Pain Index [PPI]) were measured five times across 18 months. Linear regressions were performed to predict baseline FIQ and PPI cross-sectionally. Of primary interest was a hypothesized interaction between ASES and symptom duration, which was significant in relation to FIQ but not PPI. Multilevel mixed models were performed to determine whether the same pattern existed longitudinally controlling for baseline symptom duration as an effect of time and ASES. The interaction was significant in the models for both FIQ and PPI. These results suggest that the effects of age and symptom duration on FMS are unique, and that self-efficacy plays a crucial role in moderating disease course (measured by symptom duration or time) in FMS.