Atypical heparin-induced thrombocytopenia:: heparin allergy with thrombocytosis

WE: report a truck driver with severe soft tissue contusion of both legs who developed atypical heparin-induced thrombocytopenia (HIT) after a thrombosis prophylaxis with unfractionated heparin; despite a thrombosis the patient showed a systemic allergic reaction to heparin in combination with elevation of thrombocytes and positive heparin-dependent antibodies. Six days after the initial trauma deep vein thrombosis of the left lower leg was diagnosed and fasciotomy was performed, preventing an imminent compartment syndrome. Another 5 days later the patient developed exanthema of the trunk and upper extremities and urticaria on his face, as well as severe headache. His platelet count increased from 134000/mu l to 258 000/mu l. After exclusion of other causes for these symptoms, a reaction to heparin-dependent antibodies (heparin-platelet-factor 4 complex) was demonstrated 2 days later. Thrombosis prophylaxis was changed to hirudiu (Refludan) and elevation of thrombocytes to 445 000/mu l was noted. Shortly after rinsing of an intravenous line with less than 50 IE unfractionated heparin at day 36 after trauma; ma the patient developed an anaphylactic shock, which could be managed with cortisone. We suggest that in HIT the thrombocytopenia may represent only one form of an allergic reaction to heparin. The cause of the thrombembolic event is an antigen-antibody reaction to heparin taking place on the surface of the thrombocyte. This is similar in all forms of systemic reaction to heparin application, even though the symptoms may vary. As thrombocytopenia may not be the main symptom of a heparin-induced antibody reaction - in our hospital only 5 of 10 patients with HIT - the disease should rather be named "heparin allergy". We suggest a new classification of different pattern of heparin allergy types I-IV. The new types I and II are similar to HIT types I and II. Type III is the reaction of antibodies without decrease of thrombocytes, and type IV the reaction of antibodies associated with systemic allergic symptoms.