Intact cognitive inhibition in patients with fibromyalgia but evidence of declined processing speed

Patients with fibromyalgia frequently report cognitive complaints. In this study we examined performance on 2 cognitive inhibition tests, the Stroop Color-Word Test (SCWT) and the Multi-Source Interference Test (MSIT), in 35 female patients with fibromyalgia and 35 age-matched healthy female controls. Experimental pressure pain thresholds (PPT) were determined, and fibromyalgia patients rated their current pain on a visual analog scale and completed the pain and fatigue subscales of the Fibromyalgia Impact Questionnaire. Further, all subjects completed questionnaires assessing symptoms of pain catastrophizing, depression, and anxiety. Significant group differences were found for SCWT and MSIT performance in both the neutral (N) and interference (I) conditions with slower reaction times in patients versus controls. However, no significant group differences were found for the difference (I-N) or proportion (I/N) scores, or on the number of errors made. For patients, pain experienced during PPT correlated significantly to several indices of cognition. Psychosocial variables were not related to cognitive test performance. Fibromyalgia patients performed worse on both tests but to a similar extent for the neutral condition and the interference condition, indicating that there is no specific problem in cognitive inhibition. Evidence of decreased mental processing and/or psychomotor speed was found in patients with fibromyalgia.

Fibromyalgia patients performed worse on interference tests, but no specific problem in cognitive inhibition was found. Decreased reaction time performance may instead point to an underlying problem of psychomotor or mental processing speed in fibromyalgia. Future studies should examine potential deficits in psychomotor function in fibromyalgia patients in more detail.