# Thyrotoxicosis: Unraveling the Mystery of Fever

## TL;DR

This paper presents a case of subacute thyroiditis causing prolonged fever and highlights the importance of considering thyroid disorders in diagnosing fevers of unknown origin.

## Contribution

The paper emphasizes the need to include thyroid function tests in the routine evaluation of fever of unknown origin.

## Key findings

- A 65-year-old male with prolonged fever was diagnosed with subacute thyroiditis after negative infectious workups.
- Thyroid function tests showed suppressed TSH and elevated T4 and T3 levels, confirming thyrotoxicosis.
- Corticosteroid treatment led to rapid resolution of symptoms, underscoring the importance of timely diagnosis.

## Abstract

Subacute thyroiditis (SAT) is a transient inflammatory thyroid disorder, typically following an upper respiratory tract viral infection, and can rarely present as fever of unknown origin (FUO). Considering endocrine diseases in the differential diagnosis of fever is essential to prevent delayed diagnosis and unnecessary investigations.

We report a case of a 65-year-old male who presented with a prolonged fever of two to three weeks, unresponsive to antibiotics, starting with mild upper respiratory symptoms. Extensive infectious and other workups were negative. Thyroid function tests revealed suppressed thyroid-stimulating hormone (TSH) and elevated free thyroxine (T4) and triiodothyronine (T3) levels. Thyroid ultrasound findings were consistent with thyroiditis. The patient was diagnosed with SAT and treated with corticosteroids, leading to rapid symptom resolution.

SAT can be overlooked in the evaluation of FUO, particularly in the absence of classic symptoms. Thyroid function testing can be considered in the routine workup of FUO. Treatment should be based on symptoms, with an appropriate corticosteroid regimen if needed, and proper follow-up is essential to monitor thyroid recovery and potential progression.