Background <p>Subacute thyroiditis is often misdiagnosed owing to its nonspecific symptoms, which can mimic other conditions. Accurate diagnosis relies heavily on thorough physical examination and careful interpretation of laboratory tests.</p> Case information <p>A 53-year-old female of Iranian (Persian) ethnicity was initially misdiagnosed with sinusitis after presenting with persistent anterior neck pain, fever, and worsening fatigue. As her symptoms progressed, she was later diagnosed with pyelonephritis, further delaying the recognition of her underlying condition. After multiple visits, a comprehensive physical examination revealed peripheral vision loss and thyroid tenderness. Laboratory tests eventually confirmed subacute thyroiditis. The patient was treated with a 10-day course of prednisone, resulting in rapid symptom improvement.</p> Conclusion <p>This case underscores the critical role of a comprehensive physical examination and strategic selection and interpretation of laboratory tests in accurately diagnosing subacute thyroiditis. Early recognition through thorough clinical assessment can help prevent diagnostic delays, unnecessary treatments, and prolonged patient symptoms.</p>