LAS VEGAS – If a patient complains of an itch that is "too deep to scratch," and the skin doesn’t show a cause, refer the patient to a neurologist, said Dr. Timothy G. Berger.
Dr. Timothy G. Berger
"The only thing I want the neurologist to tell me is that the patient doesn’t have multiple sclerosis," said Dr. Berger of the University of California, San Francisco.
There have been numerous reports of patients presenting with signs and symptoms of neuropathic itch who subsequently are diagnosed with multiple sclerosis. Dr. Berger commonly sees patients who are referred to him because treatment of their itching did not help, and they have neuropathic itch.
What does neuropathic itch look like? "The way to think about this is itch with other sensory findings," such as hypesthesia, he suggested at the seminar sponsored by Skin Disease Education Foundation. "We often have patients who’ve had neural or back injury" and develop itch with hypesthesia.
Many patients will say the "itch is too deep to scratch," he said. Or, the itch may be accompanied by burning or pain. There may be no primary lesion, or only erythema, in the itch area. The patient may describe the itch as sharp spasms of itch, or formication of skin (a crawling itch). Plenty of reports in the medical literature describe patients who present with delusions of parasitosis or formication who turn out to have multiple sclerosis, he noted.
A different CNS problem also can cause neuropathic pruritus: progressive multifocal leukoencephalopathy. Peripheral causes of neuropathic itch include brachioradial pruritus, notalgia paresthetica, or postherpetic neuralgia. In addition, prurigo nodularis or lichen simplex chronicus can produce neuropathic itch.
Spinal cord tumor or cervical spine disease with nerve entrapment are two of three important differential diagnoses when you see a patient with neuropathic itching on the extensor forearms, elbows, and arms that is typical of brachioradial pruritus. Consider also the possibility of polymorphous light eruption (sun allergy), Dr. Berger said. Sun exposure worsens all of these, making them difficult to distinguish clinically.
Referring patients with brachioradial pruritus to a physical medicine department or a spine center may help make the diagnosis and provide treatment and support, Dr. Berger suggested.
The itching from brachioradial pruritus tends to be worst with late-summer sun exposure and may clear in the winter. In contrast, polymorphous light eruption tends to be worst in the spring. Brachioradial pruritus is severe and causes potentially disabling itch, most commonly affecting white, middle-aged, affluent women with chronic sun damage.
Patients often use ice to stop the itching because little else seems to help. Sun protection and topical steroids may provide some relief. Lidoderm patches may also help. Some clinicians have prescribed topical Sinequan or capsaicin for brachioradial pruritus. Wrapping up the itching area in Unna’s boot occlusion for a few weeks may break the itch-scratch cycle, Dr. Berger suggested.
Other treatments that have been tried include gabapentin, paroxetine, mirtazapine, acupuncture, physical therapy, spinal cord manipulation, and transcutaneous electrical nerve stimulation (20 minutes per day for 5 weeks).
Thalidomide (25-200 mg nightly) is particularly effective for neuropathic pruritus, especially brachioradial pruritus, prurigo nodularis, or photodermatoses, but doses greater than 100 mg/day increase risk for deep vein thromboses and stroke.
Two of Dr. Berger’s patients on thalidomide for prurigo nodularis developed stroke. "Both of those patients are back on thalidomide after their stroke even though they know that thalidomide caused their stroke, because this is the only thing that stops their itch," he said.
Thalidomide also can cause neuropathy at doses greater than 25 mg/day, "so I start everybody at 50 mg every other day" and titrate up, he said. The drug also can cause constipation, weight gain, and sedation. Its slow onset of action can take weeks to show any benefit. "You have to hang in there," he added.
Dr. Joseph F. Fowler Jr., who moderated a question-and-answer session after Dr. Berger’s presentation, echoed his advice to send patients with neuropathic pruritus to neurologists.
"I see a lot of people who itch who come to me for patch testing as a kind of last resort," and only one or two had relevant patch test results when no skin disease was visible as a potential cause of itch, said Dr. Fowler of the University of Louisville (Ky.) "It can happen, but it’s not terribly common."
More commonly, if he doesn’t see much on the skin besides secondary lesions from scratching, "I immediately send them" to a neurologist, he added.
The neurologists aren’t always impressed. Dr. Fowler recalled a neurologist who was amused by the referral until imaging showed a tumor in the cervical spinal cord that was at risk of imminently severing the spinal cord and was causing referred itching.