An Unusual Case of Tinzaparin-Induced Haemorrhagic Bullous Dermatosis: Diagnostic and Therapeutic Challenges.

Haemorrhagic bullous dermatosis is a rare (<0.5%), dose-independent complication of treatment with low molecular weight heparin (LMWH), often misdiagnosed as necrotizing fasciitis or vasculitis. The case presented here underscores the importance of clinicopathological correlation in anticoagulated patients. We present a 72-year-old woman with a history of hypertension who developed tender haemorrhagic bullae on her left leg 10 days after initiating tinzaparin (a low molecular weight heparin with 70 to 120 units of anti-factor Xa activity per mg) to treat pulmonary embolism. Histopathology revealed subepidermal haemorrhage with neutrophilic infiltrates but no fibrinoid necrosis/immune deposits. The bullae resolved rapidly after switching to apixaban and local wound care. This case revealed a number of diagnostic challenges. It is important to differentiate haemorrhagic bullous dermatosis from heparin-induced thrombocytopenia-associated skin necrosis by means of the platelet count (normal in our patient), as well as to exclude vasculitis (no leukocytoclastic in our patient) and bullous pemphigoid (no immunofluorescent deposits in biopsies from our patient). LMWH-induced bullous dermatosis requires high clinical suspicion. Early biopsy and switching to direct oral anticoagulants ensure favourable outcomes. LEARNING POINTS: Delayed onset (8-10 days post-initiation of low molecular weight heparin), dose independent.Haemorrhagic bullous dermatosis is not a hypersensitivity reaction.High-risk profile: age >70 years-old, estimated glomerular filtration rate <30 ml/min, concomitant steroids, or vascular fragility.