Two contrasting post-zoster dermatomal phenomena.

A 29-year-old, normotensive, nondiabetic man presented with a 9-day history of a scaly, pruritic eruption involving the right chest, axilla, and arm. He had a history of herpes zoster involving the same areas about 4 weeks ago. The present eruption started after the herpetic lesions had healed. Examination revealed scaly, erythematous plaques and papules involving the right side of the chest, axilla, and arm in a dermatomal pattern (figure 1). Removal of the scales revealed underlying bleeding points (positive Auspitz sign). The rest of the body, including scalp, palms, soles, and nails, were normal. There was no history suggestive of psoriasis in any family member. Systemic examination and routine investigations were noncontributory. A clinical diagnosis of psoriasis was made and confirmed by histopathologic examination of a skin biopsy sample. The patient was prescribed a topical clobetasol cream and oral levocetirizine. The eruption resolved completely after 3 weeks. A 43-year-old normotensive, nondiabetic woman presented with a 2-day history of fever, arthalgias, and generalized erythematous dermatitis. Five days ago, the patient had a toothache for which she was prescribed injectable ampicillin. After receiving ampicillin for 3 days, she developed fever, myalgias, and arthalgias, which was followed several hours later by an erythematous eruption. The dermatitis started on the trunk and, over a period of several hours, progressed to involve the face and limbs. The eruption was slightly pruritic. History revealed herpes zoster 7 months ago involving left thoracic dermatomes, for which the patient was treated with valacyclovir (1 g thrice a day x 7 days) and analgesics. There was no history of post-zoster neuralgia. On examination, the patient was febrile (oral temperature 102 degrees F), her heart rate was 118 beats per minute, and her blood pressure was 110/70 mm Hg. Cutaneous examination revealed an erythematous, maculopapular dermatitis involving the face and limbs in a bilaterally symmetrical pattern; the palms and soles were also bilaterally involved. The whole of the trunk was involved with erythematous and, in places, violaceous, maculopapular eruption except for a small area on the left side corresponding to T8 and T9 thoracic dermatomes (Figure 2). Complete blood cell counts revealed eosinophilia (9%) and liver function tests, kidney function tests, random blood sugar, routine urine examination, and blood and urine cultures were noncontributory. Histopathologic examination of lesional skin biopsy revealed an intense mononuclear cell infiltration with many eosinophils and an interface dermatitis with hydropic degeneration of basal keratinocytes, while in the spared area, only slight lymphocytic infiltration was present in a perivascular distribution. Based on the history and examination, a diagnosis of ampicillin-induced drug dermatitis was made. The ampicillin was stopped and the patient was put on a short course of oral prednisolone, antipyretics, and topical calamine. The patient was afebrile in 2 days and the eruption resolved completely in 8 days.