Chapter 21 - Biomarkers of Pain: Quantitative Sensory Testing, Conditioned Pain Modulation, Punch Skin Biopsy

Abstract

Treatment of chronic pain is difficult and requires a correct diagnosis and prospective identification of treatment responders. The establishment of pain biomarkers is essential to improve therapy for patients with chronic pain. To date, no valid biomarkers have been identified for pain. However, results of previous studies indicate some promising candidates: sensory testing, i.e. quantitative sensory testing (QST) and conditioned pain modulation (CPM), as well as skin biopsies. Using a standardized QST protocol, an individual somatosensory profile can be created for each patient that reflects the underlying pathophysiologic mechanisms. Patients’ stratification according to their sensory profile may be helpful to predict treatment response and realize the concept of a mechanism-based therapy. CPM is a dynamic measurement that refers to an endogenous descending pain modulatory pathway in which a conditioning stimulus is used to affect a painful test stimulus (the pain inhibits pain phenomenon). Many different pain syndromes are characterized by a less sufficient CPM effect. Furthermore, a reduced CPM may affect treatment response and be used as a pharmacodynamic measurement to monitor treatment effect. Skin punch biopsies are an objective measurement and can be used in particular to detect small fiber neuropathies that are characterized by an abnormal intraepidermal nerve fiber density. Additional neuronal markers may be useful to predict treatment response to specific agents. Both sensory testing and skin biopsies have limitations that should first be investigated in future studies before an establishment as a biomarker is possible.