Summary

A 30-year-old woman presented with severe headache, dysarthria and right hemiparesis. She was treated for suspected viral encephalopathy and recovered over the following weeks although the headaches persisted. Two months later she was treated in-hospital for pulmonary embolism. The following year she was readmitted for increased frequency of headaches and was given a diagnosis of migraine. A subsequent MRI head scan was suggestive of longstanding venous sinus infarcts and neuroradiology review concluded that encephalitis had been the incorrect initial diagnosis. Subsequent investigations for an underlying cause of the two episodes of venous thrombosis revealed a total homocysteine level of >350 μmol/L (<15 μmol/L). An underlying diagnosis of homocystinuria secondary to cystathionine β-synthase deficiency was made although this metabolic condition is normally recognised in childhood. Treatment with pyridoxine and betaine normalised her homocysteine levels and she has had no further thrombotic event since.