MICHAEL E.MINGMD, MSCE
The skin biopsy specimen showed many dark-colored particles in the dermis and subcutis, predominantly ingested by histiocytes. The particles did not appear to be of endogenous substance. On follow-up, 1 year later, the blue discoloration had faded.
Clinically, the clear-blue discoloration had the appearance of an artificial dye. It was not consistent with a hematoma, deep deposition of melanin pigment, or an ordinary tattoo. This clinical appearance, in combination with the phagocytosed structures observed on light microscopy, strongly suggested that the particles were of exogenous origin.
Acute Blue Patch on the Forearm—Diagnosis. Arch Dermatol. 2007;143(7):937-942. doi:10.1001/archderm.143.7.937-e