D. M. Davydov

Background Fibromyalgia (FM) is a chronic pain disorder of unknown aetiopathogenesis, in which the role of activity of the hypothalamic–pituitary–adrenal (HPA) axis is not clearly established. Methods This study analysed the modulatory effects of disease chronicity and severity on cortisol levels. Hair cortisol concentrations (HCC) and clinical evaluation data (pain severity, impact of FM on daily activities, depression, anxiety, fatigue and insomnia) were collected from 47 female patients with FM and 36 healthy women (HW). Results The results showed that disease chronicity, with a negative effect, and symptom severity, with a positive effect, were independent predictors of HCC. Patients with a shorter disease duration had higher HCC than patients with a longer disease duration and healthy participants. Furthermore, patients with greater symptom severity had higher HCC than those patients with lower clinical severity and healthy participants. While disease chronicity in FM was associated with a decrease in HCC, clinical severity increased HCC. Conclusions These results support the existence of a dysfunction in the regulation of the HPA axis in FM and its possible contribution to chronic pain development. Significance This is the first study to assess hair cortisol concentrations in a specific sample of patients with fibromyalgia (FM). This method is especially useful for the assessment of long‐term regular cortisol excretion. Results showed a two‐component model for explaining cortisol levels: disease chronicity, with a negative effect, and symptom severity, with a positive effect. This suggests that severe pain/stress evokes higher cortisol levels at earlier stages of FM, while in the longer term a decrease in cortisol levels was observed.