Purpose: To describe and evaluate somatic symptoms in patients with rheumatoid arthritis (RA) and fibromyalgia, determine the relation between somatization syndromes and fibromyalgia, and evaluate symptom data in light of the Diagnostic and Statistical Manual-5 (DSM-5) criteria for somatic symptom disorder.
Methods: We administered the Patient Health Questionnaire-15 (PHQ-15), a measure of somatic symptom severity to 6,233 persons with fibromyalgia, RA, and osteoarthritis. PHQ-15 scores of 5, 10, and 15 represent low, medium, and high somatic symptom severity cut-points. A likely somatization syndrome was diagnosed when PHQ-15 score was ≥10. The intensity of fibromyalgia diagnostic symptoms was measured by the polysymptomatic distress (PSD) scale.
Results: 26.4% of RA patients and 88.9% with fibromyalgia had PHQ-15 scores ≥10 compared with 9.3% in the general population. With each step-wise increase in PHQ-15 category, more abnormal mental and physical health status scores were observed. RA patients satisfying fibromyalgia criteria increased from 1.2% in the PHQ-15 low category to 88.9% in the high category. The sensitivity and specificity of PHQ-15≥10 for fibromyalgia diagnosis was 80.9% and 80.0% (correctly classified = 80.3%) compared with 84.3% and 93.7% (correctly classified = 91.7%) for the PSD scale. 51.4% of fibromyalgia patients and 14.8% with RA had fatigue, sleep or cognitive problems that were severe, continuous, and life-disturbing; and almost all fibromyalgia patients had severe impairments of function and quality of life.
Conclusions: All patients with fibromyalgia will satisfy the DSM-5 "A" criterion for distressing somatic symptoms, and most would seem to satisfy DSM-5 "B" criterion because symptom impact is life-disturbing or associated with substantial impairment of function and quality of life. But the "B" designation requires special knowledge that symptoms are "disproportionate" or "excessive," something that is uncertain and controversial. The reliability and validity of DSM-5 criteria in this population is likely to be low.