Pulmonary thromboembolism and aortic thrombosis due to severe hyperhomocysteinemia with MTHFR C677T mutation: a case report.

Background: Hyperhomocysteinemia is a well-established risk factor for arterial and venous thromboembolism. Among the various aetiologies, a homozygous C677T mutation in the methylenetetrahydrofolate reductase (MTHFR) gene impairs the remethylation of homocysteine, promoting a prothrombotic milieu. However, simultaneous manifestations of pulmonary thromboembolism and aortic thrombosis remain exceedingly rare and clinically underrecognized. Case summary: We report a case of a 58-year-old male who presented with acute dyspnoea. Chest computed tomography angiography revealed bilateral pulmonary thromboembolisms and extensive mural thrombi in the thoracic and abdominal aorta. Laboratory findings demonstrated markedly elevated plasma homocysteine (>50 µmol/L) and a folate deficiency, and genetic analysis confirmed homozygosity for the MTHFR C677T mutation. The patient also had a history of acute myocardial infarction and ischaemic stroke suggestive of a chronic thrombotic diathesis. The patient was managed with intravenous anticoagulation and daily supplementation with vitamin B6 and folate, with gradual clinical improvement. Discussion: This case highlights the systemic thrombotic consequences of inherited hyperhomocysteinemia caused by a homozygous MTHFR C677T mutation. In the absence of conventional risk factors, the coexistence of arterial and venous thromboses underscores the importance of the early detection of genetic predispositions in patients with unexplained or recurrent thromboembolic events. Targeted metabolic correction, including folate repletion, may help attenuate the residual vascular risk in this subset of patients.