Chronic Pain and Thoracic Surgery Michael A. Erdek, MD a, * , Peter S. Staats, MD a,b a Division of Pain Medicine, The Johns Hopkins University School of Medicine, 550 North Broadway, Suite 301, Baltimore, MD 21205, USA b 160 Avenue-at-the-Commons, Shrewsbury, NJ 07702, USA Chronic pain after thoracic surgery is a difficult problem for patients and practitioners alike. Theo- ries for its etiology are multiple, and a review of definitions of pain, its types, and appropriate treat- ments is appropriate before specific consideration of pain after thoracic surgery. Pain has been defined by the International Association for the Study of Pain as ‘‘an unpleasant sensory and emotional experience associated with actual and potential tissue damage, or described in terms of such damage.’’ The same organization defines chronic pain as ‘‘pain that persists beyond the normal time of healing.’’ Although acute pain can be considered functional and mainly a physiologic response to tissue damage, chronic pain involves psychological and behavioral mechanisms in addition to the physiologic mecha- nisms [1]. It is not the duration of pain that dis- tinguishes acute from chronic pain, but the inability of the body to restore its physiologic function to normal homeostatic levels [2]. An example of this is neuropathic pain, which is chronic, often burning pain that persists secondary to nerve injury (Box 1). Prevalence of chronic pain Studies attempting to ascertain the prevalence of chronic pain are beset with challenges. The intensity of pain, survey method, and definition of chronicity vary from study to study. One group attempted to review the literature to search for the prevalence of chronic benign pain among adults (all epidemiologic studies concerning pain were included, provided that the study was not focused exclusively on acute pain or pain as a consequence of a defined disease, such as cancer or rheumatoid arthritis) [1]. Fif- teen studies were identified reporting the prevalence of chronic pain in a general population with subjects age 18 to 75 years. The prevalence of chronic pain ranged from 2% to 40% (median 15%). The inves- tigators speculated as to reasons for the large variance in pain prevalence. It would be expected that studies defining chronic pain with fewer criteria for inclusion would find a higher prevalence than studies with more inclusion criteria. In addition, the investigators surmised that data collection would influence results: Clinical examination by a physician is more stringent than self-response to a questionnaire. Finally, the review noted that the prevalence of chronic pain was higher in studies in which chronic pain was not defined or the definition was unclear [1]. Neurobiology of chronic pain The initial pain impulse usually is perceived through the primary afferent nociceptors , grouped into myelinated A-delta fiber mechanothermal and unmyelinated C fiber polymodal nociceptors. These nerve fibers are responsive to many mechanical, thermal and chemical stimuli [3]. Another important finding is that ‘‘silent’’ or ‘‘sleeping’’ nociceptors normally cannot be activated and become excitable only under pathologic conditions, such as inflamma- tion [4]. 1547-4127/05/$ – see front matter D 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.thorsurg.2004.10.001 thoracic.theclinics.com * Corresponding author. E-mail address: merdek@jhmi.edu (M.A. Erdek). Thorac Surg Clin 15 (2005) 123 – 130