Endocrine Abstracts

Background: The prevalence of iodine-based contrast media-induced (ICM-induced) thyroid dysfunction varies (1-15%). Contrast-induced hyperthyroidism is predominantly found in iodine-deficient regions and in patients with underlying nodular goitre or latent Graves’ disease. Beta-blockers are first-line therapy, but anti-thyroid medication are used for severe symptomatic cases.

Case Report: A 79-year-old man presented with a 4-day history of bilious vomiting, diarrhoea and weight loss. He had a subtotal colectomy for ulcerative colitis a year before, and since then had multiple admissions with gastrointestinal and stoma-related issues. Additional history included subclinical hyperthyroidism, ischaemic heart disease, atrial fibrillation, diabetes, asthma and depression. Regular medication included metformin, digoxin, aspirin, rivaroxaban, bisoprolol, omeprazole, venlafaxime, atorvastatin and loperamide.

Investigation and management: Initial blood results were consistent with dehydration. Inflammatory markers were normal. Abdominal x-ray demonstrated no evidence of bowel obstruction. Gastroscopy demonstrated external compression of the esophagus. A computerized tomography scan demonstrated a large multinodular goitre compressing the trachea. An ultrasound confirmed the same plus reduced vascularity. Subsequent tests revealed a serum TSH of 0.02 mU/l (normal range: 0.3-4.1), free thyroxine: 26.9 pmo/l (12-22), free triiodothyronine: 3.9 pmo/l (3.1-6.8): indicating overt hyperthyroidism. Thyroid uptake scan indicated poor uptake. Thyroid receptor antibodies and thyroid peroxidase antibodies were negative. Further history revealed the patient had undergone radiological imaging involving the use of iodine-based contrast media, on three separate occasions, within the prior three months. A diagnosis of ICM-induced hyperthyroidism was made and carbimazole was prescribed. Biochemical monitoring and tapering the carbimazole dose was performed monthly. Results returned to the usual subclinical levels after three months.

Conclusions: This patient had risk factors for ICM-induced hyperthyroidism. Although most cases of ICM-induced hyperthyroidism are mild and transient, there is a small risk of severe thyrotoxicosis with serious cardiovascular complications. Therefore, clinicians need to be aware of this adverse effect.