Malignant Pseudothyroiditis after COVID-19 Infection


Anaplastic thyroid carcinoma (ATC) is an uncommon form of cancer characterized by its rarity and poor prognosis. The incidence of ATC is significantly below six new cases per 100,000 person-years, with age-adjusted rates of 0.12 per 100,000 person-years in the US and 0.1 to 0.3 per 100,000 person-years in Europe.

Over a 30–40-year period, there has been a consistent increase in the incidence rates by approximately 3.0% and 1.3% per year in the US and Europe, respectively. Interestingly, this rise cannot be attributed to improved screening or diagnosis, as all ATC patients present with cervical compressive symptoms [1].

ATC is a rare but serious malignancy that has shown some improvement in prognosis over the past two decades due to a better understanding of its molecular mechanisms and the development of targeted therapies. However, the prognosis still remains poor, and early detection and referral to expert centers play a crucial role in improving outcomes [2].

Case Presentation

We present a case of a 60-year-old male patient who, approximately one month after recovering from a COVID-19 infection, developed a clinical presentation resembling subacute thyroiditis (SAT). However, further investigation revealed a rapidly fatal ATC. The patient’s atypical presentation and the challenges encountered in reaching a definitive diagnosis highlight the need for vigilance in identifying rare clinical entities and diagnostic delays, particularly in the context of the COVID-19 pandemic [3].


Malignant pseudothyroiditis (MPT), first described by Rosen et al. in 1978, refers to cases where SAT-like symptoms are caused by the infiltration of the thyroid gland by malignant cells. Three categories of MPT have been identified: MPT revealing a solid cancer, MPT revealing hematological malignancies, and MPT revealing anaplastic carcinoma. In our case, the patient’s clinical presentation aligned with MPT revealing anaplastic carcinoma [2].

Similarities between our patient and previously reported cases of MPT were noted, such as the age of onset (usually greater than 55 years), initial presentation with an inflammatory syndrome, progressively enlarging goiter, thyrotoxicosis, and a high FT4/FT3 ratio. However, our patient exhibited three distinct peculiarities: the association with recent COVID-19 infection, challenging cytological and histological diagnosis despite expert analysis, and the presence of a known EU-TIRADS 4 nodule [4].

The relationship between COVID-19 infection and the subsequent development of MPT is yet to be established. While no direct link has been proposed between viral infections and thyroid carcinogenesis, the possibility of a promoting role of thyroiditis triggered by COVID-19 infection requires further investigation. The complex interplay between inflammation, viral infection, and tumor growth needs careful consideration when evaluating atypical clinical presentations [5].


We present a unique case of malignant pseudothyroiditis mimicking subacute thyroiditis in a patient who had recently recovered from a COVID-19 infection. This case highlights the importance of prompt recognition and appropriate diagnostic measures in patients with atypical clinical features, particularly during the ongoing pandemic.

While rare, the potential for malignant pseudothyroiditis should not be overlooked, and timely referral to expert centers for further evaluation is crucial for improving patient outcomes. The inclusion of ultrasound examination, microbiopsy, and body CT imaging can aid in accurate diagnosis and facilitate optimal patient management.

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