Misdiagnosis of Graves' hyperthyroidism due to therapeutic biotin intervention.

Background: Lately, high dose of biotin is often given orally to patients with a primary progressive multiple sclerosis (PPMS). However, the molecule biotin is also a principle compound in various analytic immunoassays.

Clinical Case: An asymptomatic 60-year-old woman with PPMS on high dose of biotin therapy (3 × 100 mg/d) displayed abnormal thyroid function tests (TSH 0.