Striking MRI brain changes resembling leukoencephalopathy are rarely seen in classical homocystinuria. Our case suggests that reversible white matter changes (WMC) are linked to elevated plasma methionine levels arising during treatment.
A 6-year-old boy with learning difficulties and a normal MRI brain scan was diagnosed with homocystinuria (initial total homocysteine 344 μmol/L and methionine 64 μmol/L). At the age of 6.5 years, he developed superior sagittal sinus (SSS) thrombosis. Antithrombotic and homocysteine-lowering treatments were started. Due to poor dietary compliance and betaine treatment, his methionine level reached 1,285 μmol/L, and left side weakness developed. Repeat MRI scan revealed new confluent WMC in previously myelinated brain areas. Further 3-month treatment with tighter dietary control significantly dropped his methionine level (233 μmol/L) with resolution of his neurological deficit and of radiological changes.
We suggest a reversible toxicity from hypermethioninaemia as a possible source of cerebral WMC (secondary to a demyelinating process) in patients with homocystinuria. It highlights the importance of homocysteine-lowering treatment as a prevention and complete resolution of neurological complications. It also demonstrates the need to consider homocystinuria in a differential diagnosis of paediatric leukoencephalopathy.