Effect of Low-Dose Amitriptyline on Autonomic Functions and Peripheral Blood Flow in Fibromyalgia: A Pilot Study

Abstract

Amitriptyline (10-50mg) is the most common drug prescribed for the treatment of fibromyalgia. Amitriptyline influences the autonomic nervous system, as is well known; fibromyalgia is also associated with dysautonomia. The present preliminary study was designed to observe the effects of amitriptyline prescribed in a low dose (10mg) on the autonomic function tests and blood flow measurements in well-diagnosed patients with fibromyalgia. Amitriptyline (10mg) was prescribed for 3 months to 21 female patients with fibromyalgia. A standard battery of noninvasive autonomic function tests comprising of lying to standing test, hand grip test, cold pressor test, deep breathing test, and Valsalva maneuver was performed both before and after amitriptyline therapy to study the autonomic reactivity of the patients with fibromyalgia. Heart rate variability analysis was done to quantify autonomic tone (activity). Blood flow measurement around the knee joint was performed using impedance plethysmography technique. The patients were also assessed for 10 major clinical symptoms of primary fibromyalgia and state and trait anxiety (state and trait anxiety inventory) at both instances. No significant changes in autonomic activity (tone) and reactivity were observed after amitriptyline therapy. Clinical symptom score and anxiety scores (both state and trait) decreased significantly from the pretreatment values. Blood flow measurement showed significant improvement in blood flow index values at the affected sites after amitriptyline therapy. Amitriptyline therapy (10mg for 3 months) increases blood flow to the affected sites. It does not affect autonomic tone and reactivity in the patients with fibromyalgia.