Clinical Vignette Session A: Vignette Award Finalists

CASE: A 50-year-old female with chronic obstructive pulmonary disease, tobacco use and bipolar disorder presented with acute, intense substernal chest pain and heart rate of 170 bpm. She had no previous cardiac history and no similar episodes in the past. She started taking lithium 2 months earlier for bipolar disorder. Her electrocardiogram showed inferior ST depression and an incomplete left bundle branch block (LBBB). Troponin T was elevated at 0.48 ng/mL. An emergent left heart catheterization revealed non-obstructive coronary artery disease and vasospasm of the left main and left anterior descending coronary arteries which resolved with intra-coronary nitroglycerine. She remained tachycardic and the electrocardiogram later showed multifocal atrial tachycardia. A subsequent thyroid-stimulating hormone level came back low (< 0.01 mIU/L) and free T4 elevated (3 ng/dl). Thyroid stimulating antibodies were negative however thyroid peroxidase (TPO) was positive. Thyroid ultrasound was unremarkable. Despite a sub-therapeutic lithium level (0.53 mmol/L), lithium-induced hyperthyroidism was suspected given its narrow therapeutic index. Lithium was discontinued and methimazole was started. After 2 days, she became asymptomatic and converted to normal sinus rhythm; she was discharged with cardiology and endocrinology follow-up.