Subacute Hashimoto's encephalopathy, treated with plasmapheresis.

We report a patient with subacute diffuse encephalopathy characterised by rapidly progressive dementia with visual hallucinations, myoclonus and generalised seizures. She was euthyroid but showed high serum levels of thyreoglobulin and thyreoperoxidase antibodies. Hashimoto's encephalopathy was diagnosed. MRI of the brain in the acute phase demonstrated no structural abnormalities. However in the mesotemporal regions and the anterior parts of the brain, a decrease of the N-acetylaspartate and an increase of the Choline-containing compounds was found on MRI-spectroscopy. Reversal of these abnormalities was demonstrated a few months later after starting therapy. Plasmapheresis resulted in normalisation of serum levels of the antibodies and rapid clinical improvement. This observation supports the idea that a correlation exists between the serum levels of the thyroid auto-antibodies and the course of the clinical illness.