Predictors of treatment response to serotonin and noradrenaline reuptake inhibitors in fibromyalgia.

INTRODUCTION: Fibromyalgia (FM) is often comorbid with anxiety and depression. Serotonin and noradrenaline reuptake inhibitors (SNRIs) are used in the treatment of FM, depression, and anxiety, but they are ineffective in a substantial number of patients. Recently, it has been reported that FM is associated with impaired glucose metabolism. OBJECTIVES: The aim of the study was to explore the associations between insulin resistance, psychiatric comorbidities, and treatment response to SNRIs in patients with FM. PATIENTS AND METHODS: A total of 59 patients with FM and 30 healthy controls (HCs) were recruited. The study patients were classified as treatment­nonresponsive if the SNRI treatment resulted in a reduction in reported pain by less than 30%. All participants were examined by a physician and completed self­report questionnaires. Blood samples were drawn to assess fasting glucose and insulin levels and to calculate the Homeostatic Model Assessment of Insulin Resistance (HOMA­IR) values. Multivariable logistic regression models were constructed to analyze the associations between insulin resistance, psychiatric comorbidies, and the lack of response to treatment with SNRIs. RESULTS: The SNRI nonresponders (FM [T-]) had higher body mass index (BMI), fasting insulin level, and HOMA­IR values than the responders (FM [T+]) and HCs. The FM [T+] patients did not significantly differ from HCs in terms of BMI, levels of fasting glucose and fasting insulin, and HOMA­IR values. Depression, anxiety, and personality disorders were significantly more prevalent in the FM [T-] than in the FM [T+] group. Insulin resistance, depression, anxiety, and personality disorders were identified as the predictors of nonresponse to SNRI treatment. The effect of BMI on the lack of response to SNRIs was fully mediated by insulin resistance. CONCLUSIONS: Increased values of certain clinical and metabolic parameters (BMI, fasting glucose, fasting insulin, HOMA­IR) as well as the presence of psychiatric comorbidities could affect the response to treatment with SNRIs in the patients with FM.