Neurophysiology of Pruritus

Interaction of Itch and Pain

Ikoma, Akihiko MD
Rukwied, Roman PhD
Ständer, Sonja MD
Steinhoff, Martin MD, PhD
Miyachi, Yoshiki MD
Schmelz, Martin MD, PhD

From the Department of Dermatology, Kyoto University, Kyoto, Japan (Drs Ikoma and Miyachi); Department of Anesthesiology–Mannheim, University of Heidelberg, Mannheim, Germany (Drs Rukwied and Schmelz); and Department of Dermatology, University of Muenster, Muenster, Germany (Drs Ständer and Steinhoff). The authors have no relevant financial interest in this article.

Corresponding author and reprints: Martin Schmelz, MD, PhD, Department of Anesthesiology and Intensive Care Medicine, Faculty of Clinical Medicine Mannheim, University of Heidelberg, Theodor-Kutzer Ufer 1–3, 68135 Mannheim, Germany (e-mail: [email protected]).

Accepted for publication July 22, 2003.

Archives of Dermatology 139(11):p 1475-1478, November 2003.

The discovery of an itch-specific neuronal pathway, which is distinct from the pain-processing pathway, has clarified the neuronal basis for the itch sensation. Albeit being distinct, there are complex interactions between pain and itch. The inhibition of itch by pain is well known and can explain the antipruritic effect of scratching. However, the opposite effect also exists and has major clinical implications: inhibition of pain processing (eg, by spinal opioids) can generate itch. Conversely, blockade of spinal opioid receptors can be used as an antipruritic therapy. Moreover, the spinal processing of pain and itch can be modulated, resulting in a hypersensitivity or hyposensitivity to pain or itch: similar to chronic painful conditions, ongoing activity of pruriceptors can induce a spinal hypersensitivity for itch in patients with chronic pruritus. Therapeutic antipruritic approaches therefore should target both local inflammation and spinal sensitization of itch processing.