New Vistas: Intraoperative Neurophysiological Monitoring and Small-Pain-Fibers Method of Testing for Spinal Cord Assessment in Pain States

Pain is the most common patient complaint encountered by practitioners in the outpatient setting. At times, the diagnosis and treatment of a given pain syndrome can be challenging due to its subjective nature. Besides the physical examination, there are several methods for quantifying and measuring pain and sensory nerve fiber outputs. In the 1940s, a logical approach to the sensory examination was identified with defined surface areas highly correlated with specific anatomic dermatomes. These dermatomes are associated with specific nerve roots and are very useful for the clinician attempting to ascertain the source of a pain generator. The concept of current perception threshold was later developed to measure the degree of sensory deficit. There was significant variability associated with this diagnostic technique, which involved changing skin resistance. These limitations led to further evolution and development of sensory conduction testing. It is important to know the evolution of nerve testing and to differentiate small-pain-fibers method of testing from previous techniques. This chapter discusses sensory nerve conduction threshold testing and the small pain fibers method of sensory nerve interrogation.