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Hypothyroidism is associated with prolonged COVID-19-induced anosmia: a case–control study
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  • Published on:
    Response to "Persistent COVID-19 related anosmia in patients with chronic autoimmune thyroiditis: What’s behind hypothyroidism?"
    • Paraskevi C. Fragkou, Internal Medicine Consultant Fourth Department of Internal Medicine, Attikon University Hospital, National and Kapodistrian University of Athens
    • Other Contributors:
      • Sotirios Tsiodras, Professor of Internal Medicine and Infectious Diseases
      • Georgios Tsivgoulis, Professor of Neurology

    We recently published our preliminary case-control study showing that a medical history of hypothyroidism was more prevalent among COVID-19 patients with persistent olfactory dysfunction compared to controls (50% vs 8%; p=0.009) and that hypothyroidism was independently (p=0.021) associated with higher likelihood of persistent hyposmia/anosmia among patients with COVID-19 (OR: 21.1; 95%CI: 2.0 to 219.4) after adjusting for age and sex (1). As previously stated, our results are not -by any means- confirmatory of an etiologic association between hypothyroidism (or preferably chronic autoimmune thyroiditis, CAT, as aptly suggested by Rotondi et al.) and the development of persistent anosmia in COVID-19 patients (1). However, the suggetsed mechanism by Rotondi et al. strengthens our observations by proposing a possible biomolecular explanation behind our clinical observations. Indeed, chemokines that are induced by SARS-CoV-2 infection, and especially CXCL10, could act as effectors of demyelination of the central nervous system (CNS) - including the olfactory apparatus - through attraction and recruitment of T-lymphocytes (2,3). Although the proposed pathogenetic mechanism by Rotondi et al. needs further investigation and laboratory confirmation through experimental studies in COVID-19 patients with persistent olfactory dysfunction, it certainly invigorates our preliminary clinical results and sets the grounds for further research in a clinically significant post-COVID-9 seque...

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    Conflict of Interest:
    None declared.
  • Published on:
    Persistent COVID-19 related anosmia in patients with chronic autoimmune thyroiditis: What’s behind hypothyroidism?
    • Mario Rotondi, Endocrinologist Istituti Clinici Scientifici Maugeri IRCCS, Unit of Internal Medicine and Endocrinology, Lab. for Endocrine Disruptors, Pavia
    • Other Contributors:
      • Francesca Coperchini, Biologist
      • Fernando de Castro, Neurologist
      • Laura Croce, Endocrinologist
      • Antonio Oliviero, Neurologist
      • Luca Chiovato, Endocrinologist

    Thyroid hormones play a role in the development and function of virtually all human cells, including maturation of olfactory neurons. The clinical observation that patients with hypothyroidism can experience disturbances in their sense of smell was first reported more than 60 years ago, and it was subsequently confirmed in both humans and animal models. In vivo animal studies clearly demonstrated that hypothyroidism induced by anti-thyroid drugs administration in mice was associated to variable degrees of anosmia, which however promptly reverted following restoration of euthyroidism by levothyroxine replacement therapy (1).
    This latter finding was regarded as the proof that thyroxine, besides its role for correct development of the nervous system would also be involved in the genesis of new olfactory receptor neurons, a process demonstrated to be maintained also in adulthood.
    Since the early phase of the ongoing Sars-CoV-2 pandemic, anosmia was identified as a peculiar clinical symptom of COVID-19 being experienced by nearly 80% of the affected patients (2). It is now known that, at least in some cases, COVID-19 course may encompass protracted olfactory dysfunction and development of olphactory bulb atrophy (3). Thus, attention was paid to potential risk factors predicting this long-term sequela. Interestingly, Tsivgoulis et al., recently performed a prospective case–control study aimed at evaluating whether hypothyroidism could be associated to prolonged COVID...

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    Conflict of Interest:
    None declared.