Between March 2020 and February 2021, 4,332 patients were hospitalized in a university hospital due to COVID-19 pneumonia. Of this group, 1,403 patients were visited in the Respiratory Clinic 3 months after discharge. The first 66 patients in correlative chronological order presenting respiratory symptoms, radiological alterations and decreased pulmonary function test values in the post hospitalization follow-up underwent a fibrobronchoscopy with a cryobiopsy for diagnostic purposes.
Out of the 66 initial patients who underwent cryobiopsy, all 66 received HRCT follow-up at 3 months, and 48 also had HRCT at 6 months. The reasons for the lack of radiologic follow-up in the remaining 18 patients are as follows: 5 patients had HRCT performed outside the 6-month window (all showed improvement on HRCT); follow-up HRCT were not performed for 2 patients due to the normalization of pulmonary function and resolution of dyspnea; 1 patient died from systemic cryptococcosis; and 10 patients were lost to follow-up and did not have follow-up HRCT.
Basal characteristics of the study population
The basal characteristics of the study population are summarized in Table 1. Thirty-two (48.48%) patients were female with a mean (SD) age of 58.22 (9.78) years. The mean body mass index was 27.89 (3.90) kg/m2, and 15 (22.73%), 13 (19.70%) and 38 (57.57%) were current smokers, ex-smokers and never smokers, respectively. Forty-two (63.64%) patients required admission in the intensive care unit with a mean stay of 18.70 (17.90) days. Thirty-five (53.03%) patients required mechanical ventilation. The mean hospital stay per patient was 33.06 (38.11) days. The data regarding the treatment received during and after hospitalization are summarized in Table 2. Eighty-one percent (54) of patients underwent cardiorespiratory rehabilitation based on the treating physician's discretion.
Pulmonary function testing along the follow-up visits
Table 3 summarizes the pulmonary function test results corresponding to the follow-up visits at 3 and 6 months after hospital discharge. The mean forced vital capacity (FVC) at 3 months was 3.03 liters (SD 1.03) and 3.20 liters (0.84) (p=0.003) at 6 months. The mean FVC in the first second was 2.48 liters (0.84) at 3 months and 2.64 liters (0.69) (p=0.010) at 6 months. The DLCO at 3 months was 56.77% (14.50) of the predicted value and 67.11% (16.46) (p= <0.001) at 6 months.
HRCT images along the follow-up visits
The radiological findings of the HRCTs corresponding to the 3- and 6-month follow-up visits after hospital discharge are shown in Table 4. Sixty-six (100%) patients presented GGO at 3 months compared to 44 patients (91.67) (p=0.134) at 6 months. In regard to the grade of extension of the GGO at 3 months, no patient presented grade 0, 9 (14.64%) presented grade 1, 29 (43.94%) grade 2 and 28 (42.42%) presented grade 3, while 4 (8.33%), 13 (27.08%), 29 (60.42%) and 2 (4.17%) patients presented grades 0, 1, 2 and 3 GGO at 6 months, respectively (p < 0.001). Sixty-four (96.97%) patients presented septal/subpleural lines at 3 months after hospital discharge compared to 42 (87.50%) (p=0.131) patients at 6 months. With respect to the extension of septal/subpleural lines 2 (3.03%), 27 (40.91%), 29 (43.94%) and 8 (12.12%) patients presented grades 0, 1, 2 and 3 at 3 months, respectively compared to 6 (12.5%), 25 (52.08%), 15 (31.25%) and 2 (4.17%) at 6 months (p=0.010).
Histological features of the lung cryobiopsies
The histological characteristics evaluated are summarized in Table 5. Twenty-two (33.33%) patients presented Masson bodies. Regarding interstitial inflammation, 15 (22.73%) patients showed none, while 33 (50%) patients presented mild inflammation, 15 (22.73%) moderate inflammation and 3 (4.55%) patients presented severe inflammation. Immunohistochemical characterization of the inflammatory infiltrate revealed that it was mostly composed of CD3 cells and that CD4/CD8 was >1. The mean number of mastocytes per HPF was 60.05. Thirteen patients (19.70%) presented bronchiolar metaplasia, 12 (18.18%) pigmented macrophages, and 5 (7.58%) presented interstitial giant cells.
Regarding senescence, defined as the abundance of cells expressing P16, in 4 (6.06%) patients it was absent, in 39 (59.09%) mild, in 18 (27.27%) it was moderate and in 5 (27.27%) patients senescence was severe. Lymphatic vessels proliferation, labeled with D2-40, was mild, moderate, and severe in the samples of 25 (37.88%), 23 (34.85%) and 18 (27.27%) patients, respectively (Fig 1).
Factors predicting mid-term outcomes after hospital discharge
Multivariate analyses showed that patients with Masson bodies in the cryobiopsy at 3 months were less likely to have an FVC (%) < 80 at the 6-month visit (p=0.04).
P16 and D2-40 in the histological samples at 3 months after hospitalization were related to DLCO values < 70% at 6 months (p=0.02, 0.04). The multivariate regression model confirmed that lymphatic proliferation and senescence values in the histological samples at 3 months after hospitalization were independently related to DLCO values < 70% at 6 months (p=0.04) (Table 6).