A 62-year-old woman is referred to dermatology for evaluation of a pruritic rash that has been present on both soles for more than two years.
Attempts to treat it with different OTC topical creams (eg, clotrimazole, miconazole), prescription antifungal creams (oxiconazole and nystatin), and even a combination cream (clotrimazole/betamethasone) have been unsuccessful. The last eased her symptoms but yielded no lasting relief.
Her primary care provider had prescribed a month-long course of oral terbinafine (250 mg/d). When that did not help, a two-week course of oral antibiotic (cephalexin 500 mg qid) was tried. Neither had any salutary effect, so the patient was referred first to a podiatrist, who quickly sent her to dermatology.
Complaining bitterly of itching on these areas, she explains that the condition began with tiny pustules, then tiny blisters that gradually covered both insteps. She denies having any such rash elsewhere (eg, on elbows or knees or in the scalp). There is no known family history of skin problems, and no personal history of arthritis.
Just prior to the onset of this problem, she had received a diagnosis of bipolar affective disorder, which forced her to leave her job and start taking lithium. Although the lithium has helped, she remains unable to work.
On examination, the skin of both insteps is covered with discrete and confluent papules and tiny pustules on an erythematous and hyperpigmented (brown), sharply demarcated, and highly symmetrical base. As the patient said, her skin, nails, and scalp elsewhere are free of any such lesions. Given her Hispanic ancestry, her skin is phototype IV/VI.
Punch biopsy is performed and shows almost no spongiosis or edema, relatively tortuous capillary loops, and collections of neutrophils above foci of parakeratosis. Special stain for fungal elements fails to identify any sign of that family of organisms.