Diffuse melanosis cutis (DMC) is a rare presentation of metastatic melanoma characterized by a progressive blue-gray discoloration of the skin and mucous membranes.

To foster a better understanding of the clinical presentation, histological findings, and pathophysiology underlying DMC.

A systematic review of the literature was completed utilizing MEDLINE, CINAHL, Embase, and Google. Data were extracted using a protocol-driven spread sheet with all statistical analyses completed using SPSS.

The review identified 68 original cases of DMC. The mean time from diagnosis of melanoma until development of DMC was 11.48 months (95% confidence interval [CI]: 0-48.16). The mean time to death following the onset of DMC was 4.43 months (95% CI: 0.00-11.11). Histological findings were relatively consistent demonstrating intracellular and extracellular melanin deposition in the dermis, with a pronounced perivascular distribution. The pathophysiological mechanisms underlying DMC could not be definitively elucidated; however, it is hypothesized that the melanin precursors, melanin, and melanosomes liberated by cytolytic metastatic melanoma deposits are phagocytosed by dermal histiocytes, manifesting clinically as diffuse melanosis.

The cross-sectional nature of case reports, paucity of cases of DMC, and heterogeneity in reporting limit any conclusions being drawn regarding the pathophysiology of DMC definitively.

DMC heralds a poor prognosis for patients with metastatic melanoma and affected patients should be made aware of the implications of this condition on survival.