SUN-316 - De Quervain Thyroiditis Following Pneumococcal Vaccination: A Rare Case Report

Background:
De Quervain (subacute) thyroiditis is most often linked to post-viral inflammatory reactions, and vaccine-related cases have predominantly involved viral antigens. A review of the literature found no prior documented cases following pneumococcal vaccination, which contains bacterial rather than viral components, making this presentation exceptionally rare.

Case Description:
A 70-year-old male with no prior endocrine history and previously normal thyroid-stimulating hormone (TSH) levels presented to the emergency department with fatigue, poor appetite, a 20-lb unintentional weight loss, fevers, diaphoresis, mild right-sided neck pain with tenderness and mild swelling, dysphagia to solids, odynophagia, and hypertensive urgency. He reported feeling unwell since receiving the pneumococcal vaccine two weeks earlier.
Acute suppurative thyroiditis, subacute thyroiditis and toxic goiter were considered given severe neck pain and symptomatic hyperthyroidism. Laboratory studies showed suppressed TSH (0.01 mIU/L) and elevated free T4 (3.96 ng/dL). Although leukocytosis was absent, intravenous antibiotics were started due to the severity of systemic symptoms. Methimazole and propranolol were initiated for suspected toxic goiter. A comprehensive viral respiratory panel was negative. Inflammatory markers were elevated (CRP 8.6 mg/dL, ESR 108 mm/hr). Thyroglobulin antibodies were markedly elevated (708 IU/mL), thyroid peroxidase antibodies were elevated (168 IU/mL), and thyroid-stimulating immunoglobulin was negative.
Ultrasound demonstrated a heterogeneous thyroid, predominantly in the right lobe, with increased vascularity and no nodules; significant thyroid tenderness was also noted. Findings supported subacute thyroiditis, and methimazole and IV vancomycin were discontinued. The patient was treated with celecoxib and propranolol, with marked improvement within 24 hours.
At a follow-up 2 months later, ESR had improved (52 mm/hr) and TSH had normalized to 3.14 mIU/L with near-complete symptom resolution.

Clinical Lessons:
Clinicians should consider vaccine-triggered subacute thyroiditis after pneumococcal immunization, potentially mediated through adjuvant-based immune stimulation (ASIA-related mechanisms). Early recognition may prevent unnecessary antibiotics and antithyroid drugs. A thorough vaccination history facilitates timely diagnosis and management.

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