By Orly Avitzur, MD, MBA
I recently saw a patient with a cervical radiculopathy — neck pain radiating to his arm from a pinched nerve. But worse than the pain was the localized itch (pruritus) that accompanied the pain, and caused him to constantly scratch the area seeking relief.
The itch had first appeared two years ago, but resolved after an operation to remove a herniated disc. Now it was back, and despite visits to several dermatologists, two neurosurgeons and his primary care doctor, no one could explain it or provide relief.
In this week’s Neurology Today story "New Research Shows Itch Is a Lot More than Skin Deep", Anne Louise Oaklander, MD, PhD, associate professor of neurology at Harvard Medical School and Massachusetts General Hospital, explained that itch sensation is transmitted by subsets of small-fibers that may or may not also transmit pain, and that neuropathic itch can be triggered by any neurological condition that damages portions of these itch neurons.
Last October, reports Neurology Today, the NIH National Institute of Arthritis, Musculoskeletal and Skin Diseases (NIAMS) invited Dr. Oaklander and others to an invitation-only roundtable of experts to explore the underlying mechanisms of chronic itch, including its connections to the central nervous system.
Workshop participants included specialists in neuroscience, dermatology, immunology, anesthesiology, pharmacology and psychiatry. They discussed the three major causes of chronic itch: 1) skin diseases such as atopic (allergic) dermatitis, 2) organ diseases of the liver, kidney, and blood, where abnormal metabolites stimulate itch neuron, and 3) neurological causes.
Conditions such as shingles, certain types of stroke, and pinched nerves, as in my patient, are among those that can trigger itch. "Neurologists need to ask their patients about itch, and to pay attention to signs of excess scratching. If caused by neurological disease, then "we can’t really be sending these patients to dermatologists," Dr. Oaklander told Neurology Today. "What we’re talking about is neurological management."
Treatment is often difficult, but my patient was lucky. I prescribed diphenhydramine (Benadryl), an inexpensive over-the-counter drug, and, as he emailed me the next day: "It worked!!" He was lucky because most neuropathic itch does not respond to the antihistamines effective for itch from bug bites, and allergies.
"Neuropathic itch patients may need to apply prescription local anesthetics to the area, or take medications to slow excess neuronal firing," Dr. Oaklander advised, adding, "If a dermatologist can't help, best bet is to check with a neurologist interested in peripheral nerve disorders or pain."