Hyperhomocysteinemia due to pernicious anemia leading to pulmonary thromboembolism in a heterozygous mutation carrier.

Pulmonary thromboembolism is a life-threatening condition resulting mostly from lower extremity deep-vein or pelvic-vein thrombosis. A 46-year-old woman was admitted to hospital with pain on the right side of the chest and hemoptysis. On laboratory analysis, D-dimer level was elevated. Computed tomographic pulmonary angiography revealed intravascular filling defects due to thrombi in right lower lobe pulmonary segmental arteries. Screening for thrombophilic states was normal except for heterozygous mutations of both prothrombin and methylene tetrahydrofolate reductase (MTHFR 677) genes. Homocysteine level was high, and vitamin B12 level and serum ferritin level were reduced. Serum antiparietal antibody was positive, and therefore, pernicious anemia was diagnosed along with iron-deficiency anemia. After the diagnoses were established, enoxaparin followed by warfarin was started in addition to oral vitamin B12, pyridoxine, thiamine, folic acid, and ferroglycine sulfate supplementation. At the end of 8 weeks of the replacement therapy, vitamin B12, folate, and homocysteine levels and red cell volume were found to be normal, with complete resolution of the thrombus confirmed by repeat computed tomographic pulmonary angiography. We conclude that hyperhomocysteinemia due to vitamin B12 deficiency associated with pernicious anemia might have decreased the threshold for thrombosis. In addition, the presence of heterozygous prothrombin and methylene tetrahydrofolate reductase mutations might serve as synergistic cofactors triggering pulmonary thromboembolism.