Test your medicine knowledge with the MKSAP challenge, in partnership with the American College of Physicians.

A 59-year-old man is evaluated for a 3-month history of intermittent itching on the forearms. He describes the itch as deep, with a burning or tingling sensation. Scratching helps somewhat, but over-the-counter topical corticosteroids have not helped. Cooling the skin soothes the itch. He did not notice a rash until he started scratching. The itch gets worse after being in the sun, but sun exposure does not cause redness or a rash.

On physical examination, the patient shows evidence of chronic sun damage on sun-exposed skin, including hyperpigmentation and solar lentigines. A few excoriations are present on the forearms, but no significant dermatitis is observed. The patient’s sensation on the arms and forearms is normal. Deep tendon reflexes are normal in the biceps, triceps, and brachioradialis.

Which of the following is the most likely diagnosis?

A: Brachioradial pruritus
B: Polymorphous light eruption
C: Prurigo nodularis
D: Solar urticaria

MKSAP Answer and Critique

The correct answer is A: Brachioradial pruritus.

This patient has brachioradial pruritus, a form of neuropathic itch that has been linked to abnormalities in the cervical spine. Inflammation or irritation of the appropriate cervical nerves causes recurrent and persistent itching in the upper extremities, usually on the forearms, but also, in some patients, around the neck, shoulders, and upper arms. A similar type of neuropathic itch occurs on the mid, medial back, called notalgia paresthetica. Evaluation of the spine may reveal evidence of osteoarthritis or other structural abnormalities; however, in the absence of gross neurologic deficits, surgery is unlikely to be of any benefit in managing this type of itch, so aggressive radiologic evaluation is generally not recommended.

Brachioradial pruritus is an “itch without a rash.” The itch usually has a deep, crawling, or tingling sensation. There are no primary skin findings, although the skin may be excoriated and even become lichenified and hyperpigmented from repeated scratching. A response to application of ice or cold packs is very characteristic and helps clinically confirm the diagnosis. A skin biopsy is nondiagnostic.

Because this is not a histamine-mediated itch, antihistamines and corticosteroids are usually unsuccessful in treating the itch. Topical analgesics, such as pramoxine, offer short-term relief. More prolonged relief may be gained with use of gabapentin or pregabalin in some patients.

Polymorphous light eruption (PMLE) is another skin condition in which patients develop skin lesions after exposure to sunlight. A variety of skin lesions may be seen in PMLE, including urticarial wheals, papules, plaques, and vesicles. PMLE usually develops early in the spring, with the first few exposures to sunlight, and can be triggered by intense exposures. Skin lesions, rather than mere itch, are necessary for the diagnosis.

Prurigo nodularis is commonly known as “picker’s nodules.” This condition can develop in itchy skin (from whatever cause) and consists of thickened, lichenified, excoriated papules and nodules in skin that has been repeatedly scratched.

Solar urticaria is another rare condition in which exposure to ultraviolet light causes hives. It can be difficult to distinguish from PMLE.

Key Point

• Brachioradial pruritus is characterized by a deep, crawling, or tingling sensation on the forearms, shoulders, and upper back; however, there are no visible skin findings.

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