Psychological factors affecting response to antidepressant drugs in fibromyalgia.

Background: The use of antidepressant drugs in fibromyalgia is extensive despite small evidence of the real impact in the clinical practice setting. This study was aimed to evaluate the long-term efficiency of antidepressant treatment in fibromyalgia and the role of psychosocial factors in treatment response.

Methods: A total of 102 consecutive patients with fibromyalgia from primary health care centers were studied with psychopathological and psychological assessment interviews and questionnaires. Sustained release venlafaxine was added to previous treatments in flexible doses from 150 to 300 mg daily for a 6-month period. Efficacy measures included the Clinical Global Impression (CGI) scale (patient and clinician versions) and the Fibromyalgia Impact Questionnaire (FIQ) score reduction.

Results: At 6 months, 48% patients were considered responders to treatment (CGI change score 1 or 2) and 23.5% had a mild response. Of note, 57.8% had less fatigue and 31.4% had less pain. The proportion of responders was greater in the group with major depression (65%) than in those without depression (45%), but the difference did not reach statistical significance. However, the reduction of FIQ scores was significantly greater in depressed (21.1; IQR: 1.4-42.0) than in non-depressed patients (41.4; IQR: 23.6-52.6) (P<0.05). FIQ score reduction was significantly smaller in patients taking concomitant opiate treatment (P<0.01) and in patients seeking incapacitation (P<0.01).

Conclusion: Antidepressant treatment in fibromyalgia was effective in patients with and without major depression, but the functional response was greater in depressed patients. Treatment response to antidepressants might be significantly influenced by attitudinal and psychosocial factors of the disease.