Seven days after undergoing bilateral total knee arthroplasty, a 65-year-old man comes to the physician with a dark discoloration and blisters on his abdomen. Current medications include simvastatin, aspirin, and low molecular weight heparin. His vital signs are within normal limits. Examination of the skin shows multiple coalescing blisters with areas of necrosis around the umbilicus. Laboratory studies show a platelet count of 32,000/mm3. Which of the following is the most likely underlying cause of this patient's symptoms?

Question

Quizplus · Accepted Answer

Eductional Objective: This patient's thrombocytopenia (< 100,000/mm3) and the timing of his symptoms (5-10 days after initiation of heparin therapy) are consistent with heparin-induced thrombocytopenia (formerly called type 2 HIT), which occurs due to the formation of IgG autoantibodies against complexes composed of platelet factor 4 (PF4) and heparin. Subsequent clot formation leads to consumption of platelets and thrombosis, which can cause DVT, pulmonary embolism, limb gangrene, as well as ischemia and necrosis at the heparin injection site.

Seven Days After Undergoing Bilateral Total Knee Arthroplasty, a 65-Year-Old