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The number of comorbidities in individuals with fibromyalgia may be associated with the severity of fibromyalgia-related variables and the prevalence of fibromyalgia, according to study results published in the Journal of Rheumatology.

Researchers conducted this cross-sectional study on the data of 12,215 patients in a research databank to examine the relationship between a fibromyalgia diagnosis and fibromyalgia-related variables and the presence of comorbidities. A total of 9017 patients with rheumatoid arthritis and 3198 patients with noninflammatory rheumatic and musculoskeletal disorders (eg, fibromyalgia, osteoarthritis, and back pain syndromes) were included.

Binary determinations of fibromyalgia and widespread pain were used, in addition to constituent variables of fibromyalgia diagnosis such as widespread pain index, symptom severity score, and polysymptomatic distress scale. Participants were assessed for the presence of 10 self-reported comorbid conditions and several covariates.

Using nearest neighbor matching and regression adjustment treatment effect models, a positive association was established between fibromyalgia-related variables and the probability of having comorbid conditions. Patients who had ≥1 comorbidities had a polysymptomatic distress scale increase of 3.0 units, a widespread pain index increase of 1.8 units, and an symptom severity score increase of 1.2 units, as well as increase in the prevalence of fibromyalgia from 20.4% to 32.6%.

With a number of comorbid conditions increasing from 1 to ≥4, there was a stepwise percentage increase of polysymptomatic distress scale, widespread pain index, symptom severity score, and fibromyalgia occurrence. In addition, patients with ≥4 conditions were predicted to have a 55.2% fibromyalgia prevalence.

Study limitations include its cross-sectional design and issues related to the reliability and validity of self-reported data.

“Although the causal paths between comorbid conditions and fibromyalgia are complex and not easily discernible, we believe that there is substantial evidence to implicate stress as a key causal factor…including early life trauma, traumatic and post-traumatic stresses, depression; and major life stresses,” noted the study authors.