This is a prospective single-center study performed on consecutive patients who had been hospitalized for COVID-19 at the IRCCS, Humanitas Research Hospital, Rozzano-Milan, Italy in the period between March 1st and April 1st 2020 [3]. The inclusion criteria were: 1) hospitalization for COVID-19 diagnosed by real-time reverse-transcriptase–polymerase-chain-reaction assay of nasal and pharyngeal swab specimens and/or bronco-alveolar lavage fluid associated with clinical and radiological signs of pneumonia [17]; 2) primary thyrotoxicosis diagnosed during hospital stay [3]; 3) duration of follow-up ≥30 days after hospital discharge. Exclusion criteria were: 1) treatment with levo-thyroxine or anti-thyroid drugs before and at the time of first thyrotropin (TSH) evaluation; 2) treatment with drugs interfering with thyroid function after recovery of COVID-19.
The diagnosis of clinical and subclinical thyrotoxicosis was based on suppressed serum TSH values associated with high or normal serum free-thyroxine (FT4), respectively. Among 58 patients who developed a SARS-CoV2-related thyrotoxicosis [3], 23 patients (39.7%) died, whereas 6 patients (10.3%) were lost at follow-up. Therefore, 29 patients (11 females, 18 males; median age 64 years, range: 43-85) were enrolled in this prospective study. Nobody of these patients received corticosteroids during hospital stay.
The first end-point was the evaluation of serum TSH values after at least 30 days of follow-up. As secondary end-points, we also evaluated serum FT4 (24 cases), free-triiodiothyronine (FT3) (14 cases), TSH receptor antibodies (TRAb) (29 cases), thyroglobulin antibodies (TgAb) (29 cases) and thyroperoxidase antibodies (TPOAb) (29 cases) and ultrasonographic thyroid structure (29 cases) at the follow-up.
The study was approved by the Ethical Committee of IRCCS Humanitas Research Hospital, and the patients gave their consent to use the clinical and biochemical data for research purposes.
Biochemical assays
Serum TSH, FT4, FT3 were measured at 8.00 a.m. using chemiluminescent methods on the Beckman Coulter DxI 800 Access® immunoassay system. In our laboratory, the reference ranges of TSH, FT4 and FT3 were 0.34-4.80 mU/L, 7.82-17.29 pmol/L and 3.38-6.45 pmol/L, respectively. TRAb were determined using the TRACE (Time-Resoved Amplified Cryptate Emission) on the Kryptor analyzer and reference range in our laboratory was <1.8 IU/L. Overt thyrotoxicosis was defined by low TSH values and serum FT3 and/or FT4 above the reference ranges. Overt hypothyroidism was defined by high TSH values and serum FT4 and/or FT3 below the reference ranges. Subclinical thyroid dysfunction was defined when TSH was either low or high accompanied by FT4 and FT3 in the reference ranges.
Ultrasound evaluation of thyroid gland
Ultrasonographic examination of the thyroid was performed with a linear transducer 5-14 (CANON APLIO A). The echogenicity was evaluated by a standardized comparison of thyroid parenchyma with the adjacent sternohyoideus, sternothyroideus and sternocleidomastoideus muscles, in a longitudinal scan of the thyroid lobes. Thyroid volume was calculated measuring the three axes of the thyroid lobes; for all measurements, the transducer kept perpendicular the skin surface. The length was measured from the most cranial to the most caudal part of the lobe on a screen picture following the longitudinal axis of the lobe; the maximal width and depth of the lobe were measured horizontally on a screen picture cross-sectional to the longitudinal axis of the lobe, taken from the middle half of the lobe in the lateral plane. Thyroid volume was calculated for each lobe separately using the formula for a rotation ellipsoid (length x width x depth x π/6) [18].
Statistical analyses
Data were presented as median and range, unless otherwise stated. The un-paired comparisons were performed by Mann-Whitney’s and Kruskal-Wallis’ tests, whereas paired data were compared by Wilcoxon’s and Friedman’s tests. Frequencies were compared by the Chi-Square’s test, with Fisher correction when appropriate. A p value <0.05 was considered as significant.