A 30-year-old man, who has been taking lithium carbonate 1350 SR daily for 2 years for management of treatment refractory schizoaffective disorder was admitted into the mental health ward for a relapse of schizophrenia symptoms. He had recent increase in the dose of Lithium due to low level. He had no symptoms suggestive of thyrotoxicosis Neither any features suggestive of thyroiditis like neck pain, fever, or any preceding viral illness. On routine testing of thyroid function, he was found to be thyrotoxic with fT4 25.3 pmol/L (9.0-25) pmol/L, fT3 11.2 pmol/L (3.5-6.5) pmol/L, TSH 0.01 mIU/L (0.40-4.00) mIU/L. His lithium level was 0.7 milliequivalents per liter (therapeutic range 0.4-1.2). Anti-thyroid peroxidase antibody 36 U/ml (Reference range <60), anti-thyroglobulin antibody U/ml <15, thyroid stimulating hormone immunoglobulin (TSI) <0.10 IU/L. A technetium thyroid uptake scan demonstrated absent uptake as shown in figure 2. Ultrasound of the thyroid gland showed a normal sized thyroid gland with no nodules, normal vasculature, and homogenous echotexture. At this stage, a diagnosis of lithium-induced silent thyroiditis was the working diagnosis. Further investigations excluded autoimmune thyroid disease. With medical treatment and cessation of lithium, His thyroid function improved.
Treatment:
He was initially started on carbimazole 5 mg twice per day and the dose was subsequently doubled and prednisolone 25 mg per day was added. Carbimazole reached a maximum dose of 20 mg twice per day. Due to poor initial response to medical treatment and ongoing high T4 and T3 , a Thyroidectomy was considered but was not needed due to response to medical treatment as seen in his last thyroid function test showed a TSH of 0.04 mIU/L, a fT4 of 14.2 pmol/L and a fT3 of 5.6 pmol/L. His carbimazole dose was slowly reduced and he is awaiting a follow up with the endocrinology team