Acral lentiginous melanoma is the most common type of malignant melanoma in the Japanese population. In most instances, classic acral lentiginous melanoma or acral lentiginous melanoma in situ can be readily distinguished from other benign pigmented lesions by virtue of its atypical clinical appearance.
We present three cases of seemingly malignant pigmented lesions on the foot, all arising in Japanese females. Clinically, the lesions are characterized by irregular borders and variegated pigmentation closely mimicking those of acral lentiginous melanoma in situ. However, the histologic findings revealed only focal slight melanocytic hyperplasia with minimal cytologic atypia along the basal layer. Despite the malignant clinical features, thorough histologic examination failed to disclose any area with significant melanocytic atypia or evidence of malignancy.
To the best of our knowledge, similar lesions with the clinical appearance of melanoma in situ and completely lacking histologic evidence of malignancy have not been reported. We, therefore, prefer to designate these lesions as atypical melanosis of the foot to highlight the clinically apparent atypical findings and to distinguish them from malignant melanoma in situ of the foot.(Arch Dermatol. 1994;130:1042-1045)