Liver dysfunction is a common complication observed in patients with hyperthyroidism, however the dysfunction is always mild and obvious jaundice is rarely observed. We present the case of a 43-year-old man who suffered from hyperthyroidism complicated by severe jaundice. The jaundice likely occurred as a secondary consequence of cholestasis due to hyperthyroidism, since other causes such as drug-induced or autoimmune liver dysfunction were ruled out. Treatment with methimazole improved severe cholestatic jaundice in parallel with normalization of thyroid function. The mechanism of cholestasis as a secondary complication of hyperthyroidism has not been uncovered and there is no specific biochemical marker for cholestasis due to this hormonal disease at present. This case serves as a reminder that severe jaundice can be a manifestation of simple hyperthyroidism, and that administration of antithyroid drugs is an effective treatment for severe cholestatic jaundice in such cases.
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