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A Patient with Neuropsychiatric Manifestations and Thyrotoxicosis in a background of Lithium Toxicity

Arambewela MH

Neuropsychiatric manifestations are well known to occur in thyrotoxicosis. In many cases, these manifestations occur in conjunction with the systemic features of the disease, but may be the presenting symptom in some patients. We report on an elderly gentleman with, neuropsychiatric manifestations and thyrotoxicosis in the background of lithium toxicity who presented as a diagnostic dilemma.

Case report: A-70 year old man awaiting coronary artery bypass graft was detected to have thyrotoxicosis with FT4 of 2.7 ng/l(0.7-1.8) and TSH levels of 0.03 μIU/mL (0.4-4.3). A Tc 99 thyroid scan showed <1% iodine uptake suggestive of thyroiditis. He had no prior history of thyroid disorders, but has had a recent coronary angiogram. He was commenced on thioamides, lithium and small doses of prednisolone. One week after initiation of medication he presented with ataxia, dysarthria, choreiform movements and altered level of consciousness following a bout of diarrhea and vomiting and was found to have elevated levels of lithium 2.57 mmol/l(0.6-1.2) with serum creatinine of 219 µmol/l(80-120). In spite of adequate hydration, hemodialysis and normalization of lithium levels he did not show any clinical improvement. Blood and cerebrospinal fluid analysis for a possible infectious etiology were negative. This prompted an alternative diagnosis of Hashimoto’s encephalopathy (HE). Treatment with high doses of steroids led to a remarkable clinical resolution. HE also known as steroid responsive encephalopathy associated with autoimmune thyroiditis is an autoimmune thyroid disease with neuropsychiatric manifestations. Although almost all cases of HE have positive thyroid antibodies, these were repeatedly negative in our patient.

This case posed a diagnostic challenge in differentiating between acute lithium toxicity and thyroiditis with encephalopathy. The dramatic response to high dose steroids in the presence of negative thyroid antibody highlights the possible rare existence of an antibody negative steroid responsive encephalopathy associated with thyroiditis.