Histopathologic examination showed a bandlike inflammatory infiltrate consisting of lymphocytes, mainly in the papillary and reticular dermis, interspersed with extravasated erythrocytes. The hemosiderin deposits were demonstrated by a Prussian blue stain (Figure 3). These features were consistent with pigmented purpuric dermatosis. Serologic tests were negative for antinuclear antibody, rheumatoid factor, and antibodies to hepatitis B virus surface antigen and hepatitis C virus.
Purpuric Eruption on the Finger—Diagnosis. Arch Dermatol. 2005;141(10):1311-1316. doi:10.1001/archderm.141.10.1311-g