Chapter 4 Primary hyperalgesia and nociceptor sensitization

Abstract

Publisher Summary This chapter describes hyperalgesia as the enhanced pain sensitivity that often occurs after injury, inflammation or certain diseases. It is characterized by a leftward shift of the stimulus–response function that relates magnitude of pain to stimulus intensity. Hyperalgesia is a common complaint when tissue is injured and/or inflamed. It also reviews nociceptor sensitization as the neurophysiological correlate of hyperalgesia. Nociceptor sensitization is characterized by a lowered threshold for activation, an enhanced response to suprathreshold stimuli, and spontaneous discharge. The chapter focuses on the features of primary hyperalgesia and sensitization of primary afferent nociceptors. After a cutaneous injury, hyperalgesia can be found in the area of injury called “primary hyperalgesia” and also in a large, uninjured area surrounding the injury site called “secondary hyperalgesia.” Primary hyperalgesia is characterized by enhanced pain to both heat and mechanical stimuli and is thought to be because of sensitization of primary afferent nociceptors. Secondary hyperalgesia is characterized by enhanced pain to mechanical, but not heat, stimuli and is thought to be because of sensitization in the central nervous system.