Dermoscopy of fully regressive cutaneous melanoma

Metastatic melanoma of unknown origin is a difficult challenge diagnostically and therapeutically. Diagnosis of the putative primary lesion is difficult. This difficulty increases when the primary lesion has undergone complete regression.

To define the dermoscopic features of fully regressed melanoma.

A single-institution, register-based study of an unselected consecutive series of seven cases of metastatic melanoma in the lymph nodes with no known or visible primary lesion was carried out. Skin examination included dermoscopy; when a suspicious area was found, observed dermoscopic features were recorded and a biopsy was performed. Diagnosis of completely regressive cutaneous melanoma was based on clinical-pathological correlation according to widely accepted criteria.

Seven dermoscopic features were associated with completely regressive melanoma: scar-like depigmentation (100%); pink coloration of the background (100%); linear-irregular vessels (86%); globular pattern of the vessels (43%); remnants of pigmentation (86%), either macular (43%) or with a peppering aspect (43%); and white lighter transverse bands (43%). The last feature was only observed with polarized light dermoscopy devices.

Dermoscopy more accurately distinguishes the vascular, pigmentary and scarring changes of fully regressive melanoma. We believe that dermoscopy should be included in the search for a regressive primary lesion in case of metastatic melanoma of unknown origin.