Sex differences in the transition to chronic pain.

Chronic pain affects more than 50 million Americans, with women disproportionately affected by severe pain, pain interference, and overall disability. The development of chronic pain is multifactorial and often begins with an incident of acute pain associated with an injury or a surgical procedure that transitions to persistent pain lasting for months or years. Despite this, there are limited clinical studies investigating sex differences in predictors and biomarkers for the transition to chronic pain. Several preclinical animal models have been developed to gain a better understanding of the mechanisms for the transition to chronic pain, and several sex-specific mechanisms have been identified across multiple systems. These preclinical models generally involve a multiple-insult approach, in which a priming insult enhances sensitivity to a subsequent induction stimulus. There is emerging evidence from preclinical research for several male-specific and female-specific mechanisms, as well as several studies showing shared mechanisms. Here, we review the clinical and preclinical literature covering sex differences in the periphery and immune system, the central nervous system, and the endocrine system related to the transition to chronic pain. We further highlight gaps in the literature and provide recommendations for future research to understand sex-specific differences in the transition to chronic pain.