Evaluation of fluorescent staining for diagnosis of leprosy and its impact on grading of the disease: Comparison with conventional staining

Introduction: Leprosy is a chronic infectious disease caused by Mycobacterium leprae (M. leprae). Histopathological examination of skin lesion is the gold standard for diagnosis. We evaluated the possible role of fluorescent microscopy in this direction which is increasingly used for rapid screening. Aim: To compare the efficacy of auramine rhodamine stain with Ziehl-Neelsen and modified Fite-faraco staining in diagnosing M. leprae in tissue sections. Study Design: Experimental, cross-sectional and retrospective study conducted for 4 years. Methods and Materials: Skin biopsies of sixty clinically diagnosed leprosy patients were stained by Ziehl-Neelsen, Fite-Faraco and fluorescent stain. The presence of the bacilli and the bacillary index was scored for each case. The bacillary index by each staining methods were compared. Statistical Analysis: SPSS v 17 (IBM, New York) used for data analysis. Chi-Square test was used to calculate significance between differences. The p-value of <0.05 was considered as statistically significant. Pearson Correlation (r-value determined) was also used for comparison between groups. Results: Sensitivity of fluorescent stain for indeterminate and borderline tuberculoid leprosies were 100% each. Positivity rates and mean bacteriological index with fluorescent stain was higher (43.3 and 11.5 respectively) as compared to that of Ziehl- Neelsen and Fite-faraco when the bacillary load was less (bacillary index < 3). There was significant correlation between the three staining types at higher bacillary load. There was a higher mean bacillary index with fluorescent stain as well as detection of an additional multibacillary case. Conclusion: Fluorescent method is more sensitive than modified fite-faraco method in detecting lepra bacilli in tissue sections especially in cases with bacillary index less than three. With its higher sensitivity, paucibacillary cases could be upgraded to multibacillary thus affecting treatement decisions.