Fibromyalgia in patients with non-psychotic mental disorders: Prevalence, associated factors and validation of a brief screening instrument.

Background: Fibromyalgia (FM) is a chronic pain syndrome associated with significant distress and numerous unpleasant consequences. Mental health problems in people with FM have been reported in many studies. People with mental disorders are thought to be at higher risk of FM than the general population, but the prevalence has not been established.

Objective: We aimed to investigate the prevalence of FM in a representative sample of inpatients with non-psychotic mental disorders. Additionally, we aimed to assess the psychometric properties of the Fibromyalgia Rapid Screening Tool (FiRST) in the Russian-speaking population of people with mental disorders.

Methods: Consecutive inpatients admitted to the Moscow Research and Clinical Center for Neuropsychiatry for treatment of non-psychotic mental disorders were evaluated for FM by a neurologist and completed the FiRST, Beck Depression Inventory (BDI), and State and Trait Anxiety Inventory (STAI).

Results: Of the 1168 patients evaluated 9.0% met the diagnostic criteria for FM. FM was associated with being female, having a diagnosis of unipolar depression, and having higher total scores on the BDI and STAI. The psychometric properties of the FiRST were good (McDonald's omega 0.79, corrected item-total correlation greater than 0.45). An optimal cut-off point with the highest Yuden's index (J = 0.75) was >3 (AUC of 0.89).

Conclusion: FM is a common comorbidity in people with non-psychotic mental disorders, associated with being female, having a diagnosis of unipolar depression, and having more severe anxiety and depression. The FiRST can be used for the FM screening with its cut-off >3 in people with non-psychotic mental disorders.

Significance Statement: It is the first study to determine the prevalence of FM in people with non-psychotic spectrum mental disorders. The study design included a consecutive sample in a real-life setting to avoid bias. In addition, we evaluated the psychometric properties of the FM screening instrument in a population of people with mental disorders and established the cut-off. The specificity of this subpopulation is explained by both the high prevalence of pain symptoms and the overlap of some psychiatric and FM symptoms.