Neuropathic 'Itch' May Result from Multiple Clinical Syndromes
LAS VEGAS—Neuropathic itch is associated with multiple clinical syndromes, including postherpetic itch, trigeminal trophic syndrome, polyneuropathies, brachioradial pruritus, keloids and burn scars, notalgia paresthetica, and spinal cord disorders.
Simply stated, “itch is defined as ‘an unpleasant sensation that induces the desire to scratch,'” said Charles E. Argoff, MD, CPE, Professor of Neurology and Director, Comprehensive Pain Center, Albany Medical Center, New York.
An itch may protect the skin from possibly harmful events or substances. Although itch normally originates in the skin, the mucosa, and the conjunctiva, it can also arise from peripheral and/or central neurological lesions, eg, in association with a peripheral neuropathic condition or stroke.
Neuropathic itch is more likely to develop on the face, head, and neck vs the lower extremities. Many conditions that cause neuropathic itch are accompanied by other sensory complaints, such as painful and non-painful paresthesias, Dr. Argoff said.
Although the precise mechanism—or mechanisms—of neuropathic itch are uncertain, there is clear overlap as well as differences between neuropathic itch and pain. One study has suggested chronic itch can have a significant an effect on quality of life as chronic pain.
“Itch is the least understood among somatic sensations,” Dr. Argoff said. Pruitogens, substances that stimulate itch, normally activate skin receptors that then activate at least two types of C-fibers, some of which respond to heat stimuli. This may explain why heat worsens itch and cooling lessens it.
Also implicated in itch are mast cells and other substances/receptors that may explain why antihistamines and antiinflammatory agents are not effective for neuropathic itch.
In evaluating neuropathic itch, descriptive terms include itchy skin (allokinesis), hyperkinesis, and the “scratch phenomenon”: what is “normally painful may be actually (paradoxically) pleasurable in the setting of itch,” Dr. Argoff said.
“Neuropathic itch is important to recognize so that available treatments can be implemented,” he added. Treatment for neuropathic itch includes nonpharmacological therapies, such as patient education (nail cutting and wearing protective garments), use of moisturizers, avoiding warm environments, wearing loose-fitting clothing, and ultraviolet B therapy (for notalgia paresthetica).
Pharmacological therapies such as capsaicin, topical lidocaine, steroids, tacrolimus, and gabapentin may be effective; antihistamines generally are not helpful. Anecdotal reports suggest benefit with pregabalin, lamotrigine, carbamazepine, doxepin, amitriptyline, nortriptyline, paroxetine, while thalidomide has been used in refractory states.
Additional therapies include subcutaneous botulinum toxin, epidural clonidine/bupivacaine, stellate ganglion blocks, microsurgical decompression for notalgia paresthetica, neurostimulation, transcranial direct current stimulation, and low-dose naloxone.