Immune Checkpoint Inhibitor (ICI)-Induced Painful Thyroiditis: A Rare Presentation With Thyrotoxicosis

Document Type

Abstract

Publication Date

9-1-2025

Abstract

Description: Thyroid dysfunction occurs in 5% to 15% of patients undergoing Immune Checkpoint Inhibitor (ICI) therapy, such as pembrolizumab, typically presenting as painless thyroiditis followed by hypothyroidism. Although often mild and manageable, rare cases of painful thyroiditis with overt thyrotoxicosis can arise, potentially complicating treatment. Case Report: A 23-year-old female with breast cancer treated with pembrolizumab presented with 6 days of fever, chills, erythema, and tenderness at a port site. Despite port removal and antibiotics, fevers persisted with tachycardia. An infectious workup and repeat were negative. Thyrotoxicosis was identified; TSH < 0.008 mIU/L (0.35-4.94), free T4 3.23 ng/dL (0.70-1.48); thyroid tenderness and elevated ESR, consistent with thyroiditis. Free T3 was normal. Thyroid ultrasound showed diffuse gland enlargement. Initial treatment with prednisone, methimazole, and propranolol improved symptoms. After a contrast CT, fever and odynophagia worsened, managed with IV dexamethasone and increased methimazole. At discharge, she remained thyrotoxic; however, fever subsided. Endocrinology follow-up was arranged. Discussion: ICI-mediated thyroiditis, seen in cancer patients undergoing immunotherapy, typically begins with a thyrotoxic phase, often asymptomatic, and transitions rapidly to likely permanent hypothyroidism. Unlike other thyroiditis etiologies, it is not included in hyperthyroidism or thyrotoxicosis guidelines, necessitating a tailored approach. Painless thyroiditis from ICIs usually involves transient thyrotoxicosis in 5% to 20% of cases, followed by hypothyroidism lasting about 6 months, with most recovering normal function, though 10% to 20% develop permanent hypothyroidism. Unlike subacute or postpartum thyroiditis, ICI-mediated thyroiditis is painless, transitions faster (3 months vs 6-9 months), and may involve elevated TPO or thyroglobulin antibodies. Conclusion: This case emphasizes the importance of recognizing atypical patterns in ICI-mediated thyroiditis to ensure timely and appropriate intervention. The requirement for high-dose IV steroids and escalating thionamide doses highlights the severity of the condition, deviating from the usual mild and transient course of ICI-related thyroid dysfunction. This further underscores the need for close monitoring of thyroid function in patients undergoing immunotherapy to prevent complications such as thyroid storm. Guidelines recommend checking thyroid function tests every 4-6 weeks from therapy initiation and every 2-3 weeks after a thyroiditis diagnosis to detect hypothyroid conversion.

Publication Title

Endocrine Practice

Volume

31

Issue

9 Supplement

First Page

S127

Last Page

S127

Comments

AACE Annual Meeting 2025 held 2025-05-15 to 2025-05-17 in Orlando, FL, USA

Link to Full Text

Open Access

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