Platelet involvement in cutaneous small vessel vasculitis

Secretory products of platelets serve important functions in inflammation and thrombosis. Participation of platelets in the tissue reaction associated with cutaneous small vessel vasculitis has not yet been evaluated, so we systematically investigated the presence of platelet aggregates in inflamed microvessels.

Thirty-six biopsies containing vasculitis and 18 biopsies with perivascular or interface type dermatitis were reviewed and adjacent sections were immunohistochemically stained with anti-CD61 antibody recognizing GPIIbIIIa receptors on platelets and with anti-von Willebrand factor (anti-vWF) antibody.

Platelet aggregates were observed in 27 (75%) of the vasculitis biopsies and three (16.7%) of the perivascular dermatitis biopsies, of which two (11%) had traumatic vessel damage. In all vasculitis cases, platelet clumps were associated with diffuse immunostaining of the perivascular stroma with the initiator of platelet aggregation anti-vWF. In the non-vasculitis type of dermatitis anti-vWF staining remained strictly limited to the cytoplasm of endothelial cells in 10 cases, and in eight cases there was also slight diffuse perivascular staining, albeit less extensively than in vasculitis cases.

Formation of platelet aggregates appears to play a thus far unrecognized role in cutaneous small vasculitis. Secretory products of platelets will likely contribute to the inflammatory response and tissue damage in vasculitis. Moreover, platelet immunohistochemistry may be helpful in the diagnosis of microvascular damage in paraffin sections.