Steroid-responsive encephalopathy in Hashimoto's thyroiditis caused by cerebral vasculitis?

Hashimoto encephalopathy is a syndrome of encephalopathy and high serum antithyroid antibodies of still unclear pathogenesis. It may be caused by immunologically mediated cerebral vasculitis or unidentified anti-neuronal autoantibodies. We report a 24 year old patient with diabetes mellitus type I complaining about abdominal pain and vomiting and presenting with ketoacidosis, elevated CRP and thrombopenia. 14 days ago thyreostatic therapy was initiated due to hyperthyroidism. On examination she was subfebrile, somnolent and confused. Brain CT, CSF and repeated TEE were normal. Thoracal and abdominal CT showed pleural effusions and ascites without evidence septic foci. Examination of ascites ruled out peritonitis. Blood cultures were negative. The patient was diagnosed as septic encephalopathy due to sepsis of unknown origin. 2 days later level of consciousness deteriorated, she developed cortical blindness and a first generalised epileptic seizure treated with i.v. clonazepam and valproat. Emergency CCT showed a new left periventricular hypodense lesion. Subsequent T2-w MRI demonstrated multiple subcortical and cortical hyperintense lesions in both hemispheres accentuated in the occipital regions with and without contrast enhancement on T1-w-images. Dw-images and initial MR-angiography were normal. Clinical and laboratory screening for systemic vasculitis was negative. Thyroid function tests showed hyperthyroidism and markedly elevated thyroid antibodies. She was treated with a 5 day course of intravenous methylprednisolon (750mg/day) followed by oral medication. Within 2 days she was alert, fully oriented and had no persistent visual field defects. Despite clinical recovery EEG showed moderate diffuse slowing, MRI was still abnormal and repeated MRA and transcranial dopplersonography showed multiple intracranial stenoses suggestive of cerebral vasculitis. The diagnosis of Hashimoto encephalopathy was made due to typical features of the disease as impairment of consciousness and cognitive functions, seizures, pathological EEG, high serum antithyroid antibody concentrations and responsiveness to steroids. Contrary to previously reported cases MRI in our patient was abnormal and demonstrated vasogenic oedema and disruption of blood-brain-barrier due to cerebral vasculitis revealed by MRA. This case suggests that autoimmune cerebral vasculitis might be the causal link between encephalopathy in Hashimoto thyroiditis and antithyroid antibodies.