Cryptococcal antigen testing of lung tissue homogenate improves pulmonary cryptococcosis diagnosis: Two case reports

Abstract

BACKGROUND

Pulmonary cryptococcosis (PC) is an opportunistic infectious disease of the respiratory system. Lung tissue biopsies, culture of respiratory samples (e.g., sputum, lung tissue, pleural fluid, and bronchoalveolar lavage fluid), and cryptococcal antigen (CrAg) testing are helpful for a definitive diagnosis. However, these tests are sometimes falsely negative. PC is often misdiagnosed or underdiagnosed owing to the absence of obvert symptoms, poor imaging specificity, and false-negative laboratory tests.

CASE SUMMARY

We report two female patients who underwent computed tomography-guided percutaneous needle pulmonary biopsy of a lung nodule for a confirmed diagnosis. In both patients, the CrAg test on the lung biopsy tissue homogenate was positive, while the serum CrAg test was negative. Combined with the lung tissue pathology, we made the diagnosis of PC. Antifungal therapy was effective in both patients.

CONCLUSION

Given the findings of our cases and the literature review, lung tissue homogenate CrAg testing can be helpful in improving the diagnosis of PC.

Keywords: Lung tissue homogenate; Cryptococcal antigen test; Pulmonary cryptococcosis; Lung biopsy; Diagnosis; Case report

Core Tip: Pulmonary cryptococcosis (PC) is often misdiagnosed or underdiagnosed owing to the absence of obvert symptoms, poor imaging specificity, and false-negative laboratory tests. We presented two cases of PC wherein serum cryptococcal antigen (CrAg) tests were negative; however, CrAg tests using lung tissue homogenate were positive. Our report aims to highlight the dilemma in diagnosing PC, as well as a novel adjunct in the diagnostic work-up for PC–cryptococcal antigen tests on lung tissue homogenates.