The shared clinical features of psoriatic arthritis (PsA) and fibromyalgia syndrome (FMS) that have the greatest discriminating power for FMS are the number of FMS-associated symptoms and tender point count. These are the factors that can best help clinicians distinguish between the conditions.
Marchesoni and coworkers conducted a cross-sectional study in 10 Italian rheumatology centers in 2009, enrolling all consecutive patients with PsA and FMS who agreed to participate. They collected all standard clinical and laboratory data for PsA and FMS from all patients. Records were made of somatic symptoms, response to the use of NSAIDs, self-evaluated pain, general health, disability, and responses to the Fibromyalgia Impact Questionnaire. The analysis concentrated on the clinical features shared by the two conditions.
Patients with FMS had higher mean tender point and enthesitis scores and more somatic symptoms, and they responded less to the use of NSAIDs. The presence of 6 or more FMS-associated symptoms and 8 or more tender points was the best predictor of FMS.