Subacute Thyroiditis: An Unusual Presentation of Fever of Unknown Origin Following Upper Respiratory Tract Infection

Abstract

Objective:Rare disease Background:Fever of unknown origin (FUO) is a diagnosis that requires a demanding workup from physicians before confirming a diagnosis. Thyroid diseases are a rare cause of FUO. Subacute thyroiditis is an inflammatory disease that can lead to a wide spectrum of presentations. Case Report:We report a case of a previously healthy male who presented with persistent fever of 4 weeks following an upper respiratory tract infection associated with constitutional symptoms. His laboratory workup included complete blood counts (CBC), complete metabolic panel (blood urea and creatinine, liver function tests, and serum electrolytes), blood cultures, abdominal and pelvic ultrasound, and computed tomography abdomen and pelvis that were inconclusive. His thyroid function tests showed a hyperthyroid state and a thyroid scan confirmed a picture of thyroiditis. The patient was treated with Ibuprofen and then with prednisolone; he showed significant improvement over a few days and was discharged with treatment of tapering doses of prednisolone over 6 weeks. Two weeks after discharge the patient had a follow-up at an outpatient clinic and was found to be in good health with resolution of his symptoms. Conclusions:Thyroid disorders are not a common cause of FUO, and even if the clinical assessment of the patient is not suggestive of thyroid disease, we should consider it a possible cause. and thyroid function test should be performed to exclude thyroid problems.

New aspects in the pathogenesis and management of subacute thyroiditis

“…The clinical characteristics of the disease has been changing significantly for the recent years. More and more cases of painless SAT have been reported [ 29 , 34 , 35 ], with frequency reaching 6.25% in our studies published in 2019 [ 29 ], but increasing instantly during the pandemic, including virtually the majority of patients with SAT hospitalized due to COVID-19 [ 18 , 30 ]. The latter observation was primarily assigned to the frequent application of analgesics and nonsteroidal anti-inflammatory drugs (NSAID) to COVID-19 patients [ 36 ].…”

Fever of unknown origin as the major manifestation of subacute thyroiditis

“…Both antibodies were negative in our case, making silent thyroiditis less likely. A low radioiodine uptake with high inflammatory markers confirm the diagnosis of SAT ( 4 , 8 ). However, the contrast-enhanced CT scan precluded this investigation because of iodine interference with the tracer uptake by the gland.…”

“…It is a self-limiting, inflammatory thyroid disorder, probably of viral origin, that usually follows an upper respiratory tract infection and spontaneously regresses ( 2 , 3 , 7 ). Many viruses have been identified as the cause such as coxsackie, mumps, measles, and influenza viruses ( 4 , 8 ). Several case reports and small case series have reported atypical SAT appearing during or up to several weeks after resolution of COVID-19.…”

“…Inflammatory markers, ESR and CRP, are usually high during the initial phase. Other findings may include mild anemia, leukocytosis, and elevated liver enzymes during the early hyperthyroid phase ( 3 , 4 , 8 ). Despite the localized nature of the thyroiditis on cross-sectional imaging in our patient, the acute phase reactants and elevated liver enzymes prompted further investigations for SAT.…”

“…However, the contrast-enhanced CT scan precluded this investigation because of iodine interference with the tracer uptake by the gland. Ultrasound of the thyroid gland is not necessary for the diagnosis but, when performed, shows an enlarged patchy, hypoechoic thyroid with irregular margins and reduced vascularity ( 3 , 4 , 8 ). These same findings in our case prompted sonographic-guided FNAB which solidified the diagnosis by showing the typical cytologic features of SAT, including many multinucleated giant cells ( Fig.…”