Chronic pruritus: targets, mechanisms and future therapies

Pruritus (itch) is an unpleasant sensation inducing the desire to scratch. Chronic pruritus (>6 weeks' duration) is a major and distressing symptom of many diseases of dermatological, systemic, neurological or psychogenic origin. Frequently, the underlying cause of pruritus cannot be identified and causal therapy is not possible. Furthermore, chronic pruritus is frequently refractory to conventional symptomatic therapies. Recent research has revealed new neuronal mechanisms in the skin and brain, suggesting novel therapeutic targets. The efficacy of the corresponding innovative therapies has been proven in recent studies and case series. For example, topical or systemic application of specific agonists such as cannabinoids or calcineurin inhibitors can influence neuroreceptors on sensory nerve fibers of the skin and suppress pruritus. Itch-selective neurons in the dorsal horn of the spinal cord can be targeted to inhibit the transmission of pruritus to the somatosensory cortex. Anticonvulsants, antidepressants and micro-opioid receptor antagonists interfere with the sensation of pruritus in the central nervous system. Chronic pruritus of any origin leads to considerable psychosocial burden and impairs quality of life. Psychoeducational interventions, stress training, training in social competence and relaxation techniques are therefore important elements in the treatment of chronic pruritus. Increasing knowledge of the neurobiology of chronic pruritus offers new therapeutic strategies. Currently, several clinical trials are investigating the efficacy of new substances addressing neuroreceptors and cytokines in the skin and central nervous system. The present review aims to provide an overview of current neurophysiological and neurochemical therapeutic models in chronic pruritus.