MRCP2-1573

MRCP2-1573

A 38-year-old man comes to the endocrinology clinic for a follow-up appointment. He was previously investigated for hyperthyroidism and was asked to return for further evaluation by the consultant. The patient initially presented to the emergency department with palpitations and was diagnosed with atrial fibrillations. Further investigations revealed an undetectable TSH with a free T4 of 52 ng/dl. Since his discharge, he has been taking bisoprolol and apixaban, which have significantly improved his palpitations, but he still experiences them. On examination, there is no apparent neck swelling or tenderness. The patient returns with thyroid-stimulating hormone receptor antibodies that were tested and reported as undetectable. What is the next appropriate investigation?