Paediatric Autoimmune Thyroiditis Triggered by Prior SARS-CoV-2 Exposure: A Case with Transient Hashitoxicosis.

Introduction: Thyroid dysfunctions in the paediatric population can present with atypical and nonspecific systemic manifestations, making diagnosis particularly challenging. Viral infections, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), have increasingly been implicated in the onset or exacerbation of autoimmune thyroid diseases both in children and adults. This report describes a case of autoimmune thyroiditis with a transient hyperthyroid phase (hashitoxicosis) following prior exposure to SARS-CoV-2, highlighting the possible immune-mediated mechanisms of viral-induced endocrine autoimmunity that may extend to paediatric populations. Case report: A previously healthy 13-year-old boy presented with fever, asthenia, bicytopenia, and hepatic cytolysis. Extensive infectious workup, including tests for hepatitis viruses, Epstein-Barr virus, cytomegalovirus, Leptospira spp., and Coxiella burnetii, was negative, except for rhinovirus detection by reverse transcription-polymerase chain reaction. Thyroid function testing revealed elevated thyroid-stimulating hormone (11.9 μIU/ml) and positive anti-thyroid antibodies (anti-thyroid peroxidase >1000 IU/ml, anti-thyroglobulin, 2108 IU/ml). Anti-SARS-CoV-2 neutralizing antibodies were markedly increased, consistent with previous infection. Thyroid ultrasound showed diffuse inhomogeneous echotexture with a pseudonodular pattern and increased vascularity, consistent with autoimmune thyroiditis. Corticosteroid therapy led to fever resolution and normalization of laboratory parameters, followed by a transient hyperthyroid phase (hashitoxicosis) and subsequent progression to subclinical hypothyroidism. Conclusion: This case underscores the importance of thyroid function evaluation in paediatric or adult patients presenting with unexplained systemic inflammation or cytolysis following viral infections. The overlapping effects of SARS-CoV-2 and other respiratory viruses may unmask or accelerate autoimmune thyroid disorders. LEARNING POINTS: Post-viral thyroid dysfunction, including autoimmune thyroiditis, may occur after severe acute respiratory syndrome coronavirus 2 infection even in children and should be considered in the differential diagnosis of prolonged febrile or inflammatory syndromes.Hashitoxicosis represents a transient destructive phase of autoimmune thyroiditis and can mimic subacute thyroiditis or other causes of thyrotoxicosis; ultrasound vascularity and antibody profile help differentiate them.Systemic inflammation with hepatic cytolysis or cytopenias may accompany autoimmune thyroid involvement, reflecting multi-organ immune activation rather than isolated endocrine disease.Thyroid function testing (thyroid-stimulating hormone, free thyroxine, antibodies) should be included in the evaluation of patients, children or adults, with unexplained post-viral symptoms or abnormal inflammatory profiles.