Serum hyaluronic acid levels do not explain morning stiffness in patients with fibromyalgia.

To investigate the serum levels of hyaluronic acid (HA) in Korean female patients with fibromyalgia (FM) and correlate these levels with variables of disease severity including morning stiffness, we measured HA serum levels in 69 FM patients, 72 rheumatoid arthritis (RA) patients, and 71 healthy controls by enzyme-linked binding protein assay. The serum levels of HA in FM patients did not differ from those in the age-matched controls, whereas HA levels were significantly higher in RA patients than in FM patients and controls (both P < 0.001). With a cut-off value of 75 ng/mL, the prevalence of seropositivity was higher in RA patients (59.7%) than in FM patients (26.1%) or controls (14.1%; both P < 0.001). There were no differences in seropositivity between FM patients and controls, or between FM patients with severe symptoms and those with mild symptoms. The HA levels in FM patients were significantly correlated with age, age at diagnosis, age at symptom development, disease duration, symptom duration, and level of education. There were no correlations between HA levels and morning stiffness, tender point counts and scores, or Fibromyalgia Impact Questionnaire, State-Trait Anxiety Inventory, and Beck Depression Inventory scores. In our patients, the serum HA levels were not increased and did not reflect disease severity. These results suggest that serum HA is not a useful laboratory marker for diagnosis and assessment of FM.