Chronic postoperative pain and sensory changes: Two sides of the same coin?

In Europe 19% of the adult population suffer from chronic pain. Of these, 15% have chronic posttraumatic/postoperative pain [1]. Chronic pain occurs in 10–50% of all patients after surgery [2] and must be regarded as a major health problem. Recent research has revealed that sensory changes frequently accompany chronic postoperative pain and that these may be key symptoms that can help us to understand why some patients develop persistent postoperative pain and others do not [3].

The current issue of Scandinavian Journal of pain contains a clinical study by von Sperling et al. [4] that examines the prevalence, character, and sensory changes and persistent pain following breast reduction surgery. One of the main indications for breast reduction surgery is back and neck pain. In the present study breast reduction gave total relief from back and neck pain in half and partial relief in one third of the patients. Preoperative breast pain in 11 patients was fully or partially relieved in all. However, 20% suffered new and persistent pain in their breasts as a consequence of the surgery. This was only of median pain intensity 2/10 (range 0–10/10), but 7% of all patients had chronic postoperative pain of moderate to severe intensity, with significant impact on daily activities. More than half of the patients with new postoperative pain met the criteria for neuropathic pain. In concert with recent trials [3,5,6] the prevalence of persistent postoperative sensory disturbances was as high as 54%, with about half reporting hypoesthesia and one third reporting hyperesthesia. The presence of sensory disturbances was associated with increased risk for persistent postoperative pain. Young age, sensory abnormality, sensory hypersensitivity, complications to surgery (infection or haematoma) were all associated with higher risk of postoperative pain.

The present trial indicates that even though a number of patients have had their pain changed from chronic back and neck pain to chronic postoperative pain, the patient satisfaction was high both among those with and those without pain. The main reason for this was that most of the patients with persistent postoperative pain had mild pain. However, it is a concern that 7% of the patients suffer from pain strong enough to significantly affect activities of daily life two years after surgery.

In the patients most seriously affected with persistent postoperative pain, the symptoms closely resemble neuropathic pain [7]. The present trial strengthens the evidence that neuropathic sensory disturbances are closely linked to chronic postoperative pain [6]. Even though persistent postsurgical pain do not necessarily have to be accompanied by postoperative sensory disturbances, and postoperative sensory disturbances often appear in patients with no pain, previous trials support the findings in von Sperling et al.’s study [4] that postoperative sensory disturbances, especially hyperphenomena, increase the risk for chronic postoperative pain [1,3,5]. Thus, the same pathologic processes that lead to sensory disturbances will in somehow predisposed patients lead to persistent pain. Sensory disturbances clearly are due to surgical nerve injuries, i.e. nerve injuries during surgery are major risk factors for chronic postoperative pain.

Acute postoperative pain consists mainly of inflammatory pain and nociceptive pain, but neurogenic mechanisms caused by nerve injuries also contribute to acute postoperative pain. Reversible neuropathic pain may dominate from the late acute postoperative phase [8].When postoperative hyperalgesic or allodynic pain persists beyond the usual time of healing it may persist for months and years [9]. This process is considered to be initiated by peripheral nerve injury and central sensitization occurring at an exaggerated degree and causing dysfunctional adaptations of the neurons in the pain-regulating systems of the nervous tissues [10]. Drugs that reduce central sensitization and neuropathic pain, i.e. local anaesthetics (locally, regionally and/or intravenously) ketamine, α-2 agonists, gabapentinoids, glucocorticoids and even NSAIDs have been suggested as candidates for prevention of chronic neuropathic postoperative pain [8]. However, the numbers of good studies indicating pharmacologic preventive effects on persistent postoperative pain are still insufficient for firm evidence based conclusions. Other risk factors for persistent postoperative pain are preoperative pain level, preoperative pain related activity impairment, decreased preoperative experimental pain thresholds, and acute postoperative pain intensity [11].

There are solid evidence that gentle surgical techniques with minimal nerve and tissue trauma reduce the risk for persistent postsurgical pain [11]. Nevertheless, the simplest way to avoid persistent postoperative pain and nerve dysfunction is to avoid surgery that is not strictly necessary, such as, e.g. cosmetic augmentationmammoplasty [3].