A Thyrotoxicosis Surprise: Jod-Basedow Phenomenon Following IV Contrast Administration.

Jod-Basedow phenomenon (JBP) is a rare thyrotoxic condition due to increased exogenous iodine exposure, also known as iodine-induced hyperthyroidism (IIH). Historically JBP was typically seen in iodine-deficient patients when exposed to increased amounts of iodine. However, in today's era, the most common cause of JBP is exposure to iodinated contrast media commonly used in various radiological examinations and interventional procedures, resulting in massive iodine exposure. Patients with normal thyroid function usually experience no ill effects. There has been increasing use of iodinated contrast in imaging and procedures over recent decades. Deposition of iodine in the thyroid in a person with normal functioning thyroid glands would usually be autoregulated and inhibited by the Wolff Chaikoff effect. However, a small albeit a significant portion of patients, particularly those with pre-existing thyroid conditions, can escape this auto-regulatory effect and be subject to life-threatening conditions, such as arrhythmias, heart failure, pulmonary arterial hypertension, cerebrovascular and pulmonary embolism, and cardiomyopathy. We present a case of a 59-year-old female with pre-existing goiter who presented with altered mentation and seizures, requiring endotracheal intubation for airway protection. She underwent a CT angiogram of the head and neck for a suspected stroke, receiving iodinated IV contrast in the process. Thyroid function tests on admission showed a thyroid-stimulating hormone (TSH) of 0.974 mIU/L (reference range 0.465-4.650 mIU/L) and free T4 of 0.46 ng/dL (reference range 0.75-2.19 ng/dL). The ensuing ICU course was complicated by thyrotoxicosis eight days after contrast administration with a surge of free T4 from 0.46 ng/dL on admission to 4.07 ng/dL and a TSH suppression to <0.015 mIU/L. She subsequently required three sessions of emergent plasmapheresis to remove excess free T4 before undergoing partial thyroidectomy and cardiac catheterization. Iodine-induced hyperthyroidism solidifies the need for awareness of a potential JBP following contrast administration, especially in an aging population and undiagnosed thyroid conditions, and timely diagnosis and intervention can greatly influence outcomes.