A unilateral sympathetic blockade does not affect stress-related pain and muscle activity in patients with chronic musculoskeletal pain.

Objective: Chronic musculoskeletal pain is often exacerbated by mental and social stress. The association between stress and musculoskeletal pain is potentially mediated by peripheral sympathetic nerves, either directly or indirectly through muscle activity. In the present study we wanted to determine whether sympathetic blockade could affect either the pain or the muscular activity experienced during mental stress in patients with chronic musculoskeletal pain.

Methods: We performed a unilateral anaesthetic blockade of the lower cervical sympathetic ganglion (ganglion stellatum) in 18 patients with chronic musculoskeletal pain (10 with fibromyalgia and eight with chronic shoulder/neck pain). After the blockade the patients performed a 60-minute stressful task with low-grade mental stress that has induced pain and muscle activity in earlier experiments. Surface electromyography (SEMG) of the forehead, temples, neck, and shoulders, and heart rate and blood pressure were recorded together with ratings of pain.

Results: We did not find any side or sidextime effect for pain or muscular activity in any of the four muscle groups (p>0.12).

Conclusion: We investigated the potential involvement of peripheral sympathetic nerves in stress-related musculoskeletal pain. A peripheral sympathetic block did not affect pain and muscle responses to a stressful task. Other explanatory models should be implemented and tested experimentally to further investigate the clinical impression that mental stress exacerbates pain in patients with chronic musculoskeletal pain.