Incidental diagnosis of medullary thyroid microcarcinoma in COVID-19 patient with elevated procalcitonin levels.

A 38-year-old male patient was admitted to the Medical Intensive Care Unit during the second wave of the coronavirus disease (COVID-19) pandemic presenting with fever, headache, muscle pain, and cough. The low-dose chest computed tomography (CT) result was normal, but an increased serum level of procalcitonin (PCT) was detected. Due to COVID-19, pronounced symptoms, and increased inflammatory markers, empiric antibiotic therapy was started. PCT level remained elevated despite 7 days of antimicrobial treatment. Hence, the diagnostic evaluation of the patient was expanded, and we identified medullary thyroid microcarcinoma. After diagnosis, a total thyroidectomy with cervical lymph node resection was performed, and the patient was discharged with oral levothyroxine. Control measurements of serum calcitonin and 18F-fluorodihydroxyphenylalanine positron emission tomography (18F-PET/CT) showed cervical and mediastinal lymph node metastases. Beside surgical treatment, the patient was not motivated for any adjuvant therapy and no new lesions were detected on control PET/CT two years after. In conclusion, clinicians should also consider malignancies such as medullary thyroid carcinoma as a potential cause of increased PCT levels, and as a next step should measure serum calcitonin level and perform neck ultrasound.