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Cutaneous reaction to low‐molecular‐weight heparin

A 33-year-old woman with a previous history of lower limb deep vein thrombosis received thromboprophylaxis with subcutaneous unfractionated calcium heparin during pregnancy. She developed an erythematous skin reaction to heparin injections. The preparation was changed to sodium heparin and then to low-molecular-weight heparin (dalteparin), but she reacted to all (left). A re-challenge with dalteparin a few months after delivery caused a similar reaction 2 d following an injection. A skin biopsy was performed. A haematoxylin ⁄ eosin-stained section of the biopsy showed marked mononuclear cell infiltration, intense perivascular cuffing and occasional mast cells within the perivascular inflammatory infiltrate (right). There was no evidence of eosinophilic infiltration, vasculitis, vascular occlusion due to thrombosis or extravasation of red cells. The combination of delayed onset and the histological features suggests that cell-mediated type IV delayed hypersensitivity plays a role in the pathogenesis of heparin-induced skin reactions.