Revisiting the Utility of Histopathological Examination of Biopsy: A Necessity in Microbiology

Abstract

Introduction: Culture is the gold standard, while potassium hydroxide mount is simplest technique used for diagnosis of fungal pathogens. Histopathological examination is the only definitive means to identify certain uncultivable fungi. Aim: To analyse role of histopathological examination and potassium hydroxide (KOH) mount for diagnosing fungal infections by correlating them with culture. Materials and Methods: In this nine year retrospective study, all biopsy specimens submitted for microbiological examination were included. Histopathological examination of biopsies of cases with positive microbiological findings on either KOH mount or culture was carried out. Any discrepancy between histopathology interpretation and microbiology KOH or culture results, taking culture as the gold standard, were noted. Statistical Analysis: Open Epi software was used for statistical analysis. Comparisons between groups were made by using the chi-square test. A p-value < 0.05 was considered statistically significant. Cohen’s Kappa coefficient (κ) was calculated as a measure of agreement between different variables. Results: Concurrent pathology specimen could be obtained in 70 samples positive for fungal elements in either KOH or culture. Thirty-two cases were positive for fungi in culture, of which 16 were correctly identified by histopathological examination. Histopathological examination was strongly associated with culture result. KOH mount was in good agreement with positive culture result for yeast. Eleven culture negative but KOH and histopathology positive cases included seven samples with hyphae suggestive of zygomycosis, and two cases of rhinosporidiosis. Allergic mucin was strongly associated with Aspergillus species. KOH mount and detection of allergic mucin on histopathological examination were found to be excellent complementary tools for diagnosing Aspergillus species. Necrosis was highly specific for fungal growth in culture and had good positive predictive value. Conclusion: We advocate using histopathology, culture and KOH examination in an integral manner to avoid potential lapses in patient management.

Keywords

• culture
• fungal infections
• potassium hydroxide mount