Histologic examination of the biopsy specimen showed subcorneal and intraepidermal neutrophils, epidermal intercellular edema, and a mononuclear cell infiltrate in the upper dermis. Focal reticular degeneration was noted. No eosinophils were seen. The histologic findings were consistent with AGEP.
Ten weeks after the patient was discharged from the hospital, prick and intradermal skin testing was performed with penicillin G, benzylpenicilloly polylysine (Pre-Pen), and benzylpenicilloate at maximum concentrations. The results were all negative. The patient was then given 250 mg of amoxicillin as an oral challenge. Three hours later, she developed nausea, headache, pruritus in her hands and feet, and severe facial flushing. Her temperature rose to 39.9°C. She vomited twice over the following 12 hours, and in the morning she was noted to have a recurrence of diffusely scattered, small, white pustules similar to the ones that were seen during her initial exposure to antibiotics. Laboratory tests showed a white blood cell count of 11 400/mm3, with 96% neutrophils (52% polymorphonuclear leukocytes and 44% stab cells). The results of IgE radioallergosorbent tests were below detection, and those of IgG radioallergosorbent tests were nondiagnostic. Oral prednisone therapy (50 mg/d for 5 days) was initiated, resulting in eventual resolution of the pustules. The patient was advised to avoid all future contact with penicillin derivatives.