Functional and structural assessment of patients with and without persistent pain after thoracotomy.

Abstract

Persistent pain is frequent after thoracotomy, with a reported prevalence of up to 60%. It remains unclear why some patients develop pain, whereas others do not. We therefore examined patients with and without pain after thoracotomy to identify pathophysiological contributors to persistent pain. Twenty patients with persistent pain, 12 patients without pain and 20 healthy controls underwent detailed functional and structural assessment including psychometric and neuropathic pain questionnaires, bedside examination for pinprick hyperalgesia and brush allodynia, quantitative sensory testing according to the protocol of the German Research Network on Neuropathic Pain, measurement of capsaicin-evoked flare response, intradermal nerve density as determined by skin biopsies and laser- and heat-evoked potentials. Bedside testing revealed evoked pain in 16 of 20 patients with pain, but only in 2 of 12 patients without pain (p<0.001). Quantitative sensory testing showed increased mechanical pain sensitivity (p=0.018) on the operated side in patients with pain, but there were no differences between the two patient groups with regard to intradermal nerve fibre density, area and flux following capsaicin application and laser- and heat-evoked potentials. Different and individual pathophysiological mechanisms of pain may obscure the clinical picture and thus preclude identification of a specific pain profile in patients with persistent post-thoracotomy pain. Evoked pain is more frequent in patients with pain. Assessment of intradermal nerve density, capsaicin-induced flare response and contact and laser heat-evoked potentials revealed no differences between pain patients and pain-free patients.