The contribution of histopathology to the diagnosis of tuberculosis. Lessons from archival biopsy samples.

Background: Histopathological analysis of tissue samples is an ancillary complementary diagnostic tool in tuberculosis (TB) with variable sensitivity and specificity according to different clinical settings. We evaluated the spectrum of histological findings, their diagnostic sensitivity, diagnostic utility, and requests over time in a sample of archival biopsies.

Methods: Analysis of biopsies of confirmed TB cases between years 2011-2019 at a reference hospital in Chile.

Results: The series included patients with a histological study for TB confirmed by culture (88.9%) or PCR (11.1%). In total, 34 samples were available for analysis, most of them of extrapulmonary origin (82.4%). Biopsies were taken before the start of treatment in 26 cases (76.5%) or after the start-end of treatment for different reasons in 8 cases (23.5%). Restricting the analysis to the group with pretreatment biopsies, the prevalence/diagnostic sensitivity of granulomas was 93.3%, 69.2% for caseous necrosis, 26.9% for granulomas with caseous necrosis without acid-fast bacilli (AFB), and 46.2% for AFB in any histological context. A histological score was constructed to evaluate the homogeneity of lesions, observing that 76.9% had at least four of the six components of the score. The request for biopsies was maintained over time despite the increase in the use of molecular techniques. The presence of AFB contributed to the diagnosis before microbiological results in 23.1% of the cases.

Conclusions: Histological study continues to contribute to the diagnosis of TB, especially in extrapulmonary forms.