Background: Diagnosis of naevus lesions may be complex where they contain little or no pigmentation. Naevus spilus (or naevus on naevus) is, generally, readily identified by the difference in pigmentation between overlying and underlying naevi and healthy skin. Malignant transformation of naevus spilus is rare. We report two cases of melanoma in which surgical procedures revealed underlying melanocyte lesions, diagnosed at histology but undetectable on clinical examination.
Patients and methods: Two patients were operated for melanoma in which surgery, at a site remote from the melanoma, suggested incomplete relapse despite the fact that previous clinical examination had indicated healthy skin. A diagnosis was made of melanoma in invisible naevus spilus.
Discussion: Diagnosis of melanoma in invisible naevus spilus may be suspected where several naevi are found together in a specific area. The main problem is the therapeutic stance to be adopted since complete excision of the underlying naevi is difficult in practice. Wood's light examination may be helpful.