A 50-year-old woman is referred to dermatology for evaluation of a rash that, for the past 30 years or so, has recurred episodically three to four times a year. Each occurrence lasts an average of three to six days and is always accompanied by a single symptom: a burning sensation confined to the rash itself. The patient denies concurrent weakness or illness and is otherwise healthy, with no history of hypertension, chronic diarrhea, flushing, or blushing. There is no family history of similar problems. The dermatology appointment was made on an urgent basis, since she is experiencing an episode.

Over the years, the patient has been seen by a number of providers. Although blood tests were negative for connective tissue diseases such as lupus, she has never seen a dermatologist or had a biopsy done on her rash. Extensive history taking failed to establish any connection between her episodes and the season in which they occurred. Stress did not seem to be a precipitating factor, nor were there any known alleviating factors, despite the many topical and oral medications that have been tried.

On examination, the rash is seen to involve the entire chest, with a strikingly bright purplish-red macular process that is also seen on the anterior neck. The portion of the neck shaded by the chin is spared. The erythema is highly blanchable on digital palpation and nontender, and it extends faintly onto the sides of the face. The eyelids, dorsal hands, and periungual areas are also spared. Forceful stroking of the skin fails to provoke urtication.

ANSWER
The correct answer is amyopathic dermatomyositis (ADM; choice “d”), details of which are discussed below. Contact dermatitis (choice “a”) would have itched, not burned, and would almost certainly have involved surface disruption such as vesiculation and/or scaling.

Polymorphic light eruption (choice “b”) presents as an exaggerated photosensitivity that typically begins early in the spring, with a “hardening” effect as summer goes on, yielding far less rash. But it itches and doesn’t burn, as with our patient. Even though it has a wide range of clinical expressions (hence the term polymorphic), it would more likely involve the dorsal arm, and there would probably be epidermal disruption, such as blistering or papular formation.

Pheochromocytoma (choice “c”) is a benign tumor (with malignant potential) that secretes a vasoactive peptide, which can result in hypertension, tachycardia, flushing, and blushing. But it would be unlikely to produce symptoms of burning, and it is quite unlikely to be active and stable for all those years without progression.

DISCUSSION/TREATMENT
The punch biopsy showed results consistent with possible dermatomyositis, confirming the striking clinical impression of a rash that feels like an exaggerated sunburn, even sparing neck skin shaded by the patient’s chin. The total absence of muscle weakness, added to the classic rash and biopsy results, means the patient probably has ADM, an unusual condition of unknown etiology, and not classic clinical dermatomyositis.

Too few cases of ADM have been seen to be able to draw many conclusions about prognosis or to try to explain why this form exists at all. Blood work has been ordered to assay levels of muscle enzymes, to rule out muscular involvement.

With classic dermatomyositis, there would be a mandatory search for a possible triggering occult malignancy, but this seems quite unlikely, given the chronicity and lack of progression in this patient’s condition. If no other major information is uncovered, we’ll likely treat her with initially high doses of steroids (120 g triamcinolone intramuscular or by infusion). But given her history, a cure is not likely to be forthcoming.

This case emphasizes the value of not only asking patients key questions but believing their answers. A burning sensation, if different enough from pure pain or itch, has a very narrow differential—the main item on which is dermatomyositis. As usual, it also highlights the value of simply knowing that a particular disease exists, which is what often prompts the search. Indeed, the lack of such knowledge is what kept this woman’s diagnosis in the dark for so many years.