Pathomorphological aspects of heparin-induced thrombocytopenia II (HIT-II syndrome).
The therapeutic use of heparin results in thrombocytopenia in 5-30% of patients. In 0.1-1% of patients treated with heparin, the platelet count decreases to between 100 x 10(9)/l and 50 x 10(9)/l and leads to severe synchronous central arterial and venous thrombosis with a mortality of 18-36%. This is known as "white-clot syndrome" or heparin-induced thrombocytopenia II (HIT-II syndrome). Whilst the clinical aspects and the central type of thrombosis in HIT-II syndrome are well documented, the histomorphology and differential diagnosis of thrombosis are not. We report three cases of HIT-II syndrome with thrombosis of the central arteries and veins. The HIT-II thrombi could be differentiated from thrombi of other origins, particularly from mural thrombi. Heparin-induced thrombi were seen on microscopical examination to be like onion skin in structure, and immunohistochemistry showed that they had a markedly reduced content of fibrin and clearly enhanced amounts of IgG and IgM. The layered structure thus implied appositional growth. The thrombi in HIT-II syndrome do not seem to be induced by activation of the coagulation cascade, but by platelet aggregation mediated by anti-platelet antibodies.
Hermanns
B
B
Institute of Pathology, Medical School of the Technical University of Aachen, Germany.
Janssens
U
U
Handt
S
S
Füzesi
L
L
D000368:Aged; D001323:Autoantibodies / Q000032:analysis; D017809:Fatal Outcome; D005260:Female; D005337:Fibrin / Q000378:metabolism; D006493:Heparin / Q000009:adverse effects*; D006801:Humans; D007074:Immunoglobulin G / Q000032:analysis; D007075:Immunoglobulin M / Q000032:analysis; D007150:Immunohistochemistry; D013921:Thrombocytopenia / Q000139:chemically induced / Q000473:pathology*; D013927:Thrombosis / Q000276:immunology / Q000378:metabolism / Q000473:pathology*
D001323:Autoantibodies; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D005337:Fibrin; D006493:Heparin