AMELIA ISLAND, FLA. — Neurogenic sources should be considered in patients who have severe pruritus for which a cutaneous cause can't be found, Dr. Jeffrey D. Bernhard said at a symposium sponsored by the Dermatology Foundation.
In many of these cases, there is a nonspecific rash that is caused by the patients' repeated scratching rather than by the disease itself, which can lead to misdiagnosis.
“Patients who scratch a lot can end up with a nonspecific rash that may be eczematous in nature. Don't assume there isn't an underlying noncutaneous cause,” said Dr. Bernhard, professor of medicine and physiology in the division of dermatology at the University of Massachusetts, Worcester.
Notalgia paresthetica and brachioradial pruritus are two examples of severe itches that arise in the peripheral nervous system rather than on the skin.
Localized pruritus of the midback, called notalgia paresthetica (NP), occurs in about 10% of the population. For most people, it's simply an occasional annoying itch. But in a small number of individuals, it manifests as a severe, constant pruritus on a patch of skin in one or both of the medial scapular borders that may be accompanied by numbness, tingling, formication, burning, hyperalgesia, and tenderness.
Associated findings also may include hyperesthesia, along with reductions in pinprick sensitivity, light-touch sensation, two-point discrimination, temperature sensitivity, and sweat response. Although NP does not ordinarily produce visible skin changes, there may be hyperpigmentation over the pruritic area and sometimes a “ragged spot” on a blouse or shirt, both caused by the patients' persistent scratching and/or rubbing.
The condition is believed to result from spinal nerve impingement. In a study of 43 NP patients with 61 lesions, 34 patients had vertebral pathology—including degenerative changes and herniated nucleus pulposus—on spinal radiography. In 28 of the 34, the changes were most prominent in the vertebrae that corresponded to a lesional dermatome (J. Am. Acad. Dermatol. 2005;52:1085–7).
The authors speculated that spinal pathologies that cannot easily be diagnosed radiographically, such as cervical fibrous bands or muscle spasms, also might contribute to NP. They urged physicians who are treating the neuromuscular problems in these patients to consider pruritus in the list of signs and symptoms of spinal disease.
Another study of 12 NP cases found dorsal arthrosis or spinal static disequilibrium on spinal x-ray in 9 patients. Symptoms improved in four of six patients who underwent spinal and paraspinal ultrasound or radiation physiotherapy. Those authors noted that capsaicin has been reported to relieve symptoms in some NP patients, but only transiently (J. Eur. Acad. Dermatol. Venereol. 1999;12:215–21).
NP is an uncomfortable condition, but brachioradial pruritus (BP) can be excruciating. Patients describe BP as a “horrendous itch” that has a “tingling, prickling, sometimes burning sensation.” It also is commonly associated with abnormal pinprick and temperature sensations. In contrast to NP, in which patients may scratch and rub to alleviate the itch, patients with BP sometimes actually gouge their forearms attempting to alleviate the sensation, Dr. Bernhard noted.
As with NP, evidence suggests that BP also arises from nerve compression or damage. In a retrospective study for which Dr. Bernhard was a coinvestigator, a chart review of 22 patients with BP seen between 1993 and 2000 showed that in all 11 for whom cervical spine radiography had been performed, the cervical spine disease correlated with the location of the itching (J. Am. Acad. Dermatol. 2003;48:521–4).
In another study of seven consecutive BP patients, electrophysiologic studies of the median, ulnar, and radial nerves yielded abnormal responses diagnostic of cervical radiculopathy in four. One of those patients had polyneuropathy secondary to diabetes. Six of the seven reported sunlight as a trigger for their itch (J. Am. Acad. Dermatol. 2003;48:825–8).
Indeed, BP also has been named “solar pruritus” because of this curious sun-triggering phenomenon. One recent study attempted to determine whether BP was, in fact, caused by a nerve compression in the cervical spine or by prolonged exposure to sunlight. Skin biopsy specimens collected from itchy skin of 16 BP patients revealed cutaneous innervation visualized by antibodies against protein gene product 9.5 (general neuronal marker), by antibodies against calcitonin gene-related peptide (marker for thin sensory nerve fibers), and by antibodies against VR1-receptor (marker for capsaicin-sensitive nerve fibers).
Compared with controls, the BP patients had reductions of 23%–43% in various nerve fibers. Itching of the arms or shoulders was seasonal in all but two of the patients, occurring more often during August-December than during the rest of the year (J. Am. Acad. Dermatol. 2005;52:142–5).
“The temporal course of brachioradial pruritus and the [histologic] changes in the skin similar to those caused by ultraviolet light indicate that sunlight is an eliciting factor and that cervical spine disease can be a predisposing factor,” the authors wrote.