Case 1 was a 51-year-old Japanese woman. She presented with an asymptomatic brown macule located on the right axilla of 2 months’ duration. The smooth macule was 2 cm in diameter with a sharp demarcation (Fig. 1A).
Case 2 was a 62-year-old Japanese man. He presented with asymptomatic, symmetric, gray–brown macules located on the groin, axillae, and popliteal region of 6 months’ duration. The smooth macules were several millimeters to centimeters in diameter and sharply demarcated (Fig. 1B).
Oral or nail lesions, previous inflammatory processes in affected areas, and internal malignancies were absent. A causal relationship with drugs, recent sun exposure, or trauma could not be identified. Findings for work-up, including blood cell count, fasting blood sugar levels, liver function, serum electrolyte levels, serum electrophoresis, urinalysis, antinuclear antibodies, and serological examinations for human hepatitis viruses and syphilis, were within normal limits or negative. The lesions gradually disappeared without medication within 6 months.
Biopsy specimens showed a lymphocytic infiltrate with basal vacuolar changes and prominent melanin incontinence in the upper dermis (Fig. 2A). The band-like lymphocytic infiltrate was moderate in Case 1 and mild in Case 2. Immunohistochemistry showed infiltrative CD8+ T lymphocytes with keratinocytic damage, indicating cytotoxic injury of the keratinocytes (Fig. 2B). Both the epidermis and the upper dermis contained CD1a+ cells (Fig. 2C). The keratinocytes focally and weakly expressed HLA-DR (Fig. 2D). These findings were identical in samples from both patients.