ACAs may not always respond to immunotherapy and can be associated with other autoimmune disorders.

Case: A 17-year-old woman presented to us in thyroid storm along with acute onset opthalmoparesis and gait ataxia. She also had acute systolic heart failure. An inflammatory CSF profile and cauda equine nerve root enhancement on MRI made the clinical picture most consistent with Miller-Fisher syndrome, with minimal response to plasmapheresis (PLEX). Over the next several months a severe pan-cerebellar syndrome ensued, failing to respond to multiple trials of immunotherapy (IVIG, corticosteroids, and PLEX). Thyroidectomy and achievement of euthyroid state had no impact on her neurological status. She is now bedbound.

ACAs associated with a hyper- or hypothyroidism have generally been reported to have shown a good response to treatment of the dysthyroid state. Our case is unique in that we found an unidentified but novel antibody reactive against mouse cerebellum, which did not respond to immunotherapy or correction of hyperthyroidism, and had an initial presentation of Miller-Fisher Syndrome. More cases of patients with the same antibody are needed to permit further study and identification of the antibody involved in this case.