Evaluation of Slit-Skin Smear Against Punch Biopsy in Diagnosing Leprosy: A Cross-sectional Study in a Tertiary Care Centre of West Bengal

Abstract

Background: Leprosy is an infectious disease which faces diagnostic challenges. Slit-skin smear (SSS) is an age simple diagnostic technique, yet not commonly applied by health care providers. The study aimed to determine the effectiveness of SSS in terms of validity, diagnostic accuracy, and percentage agreement against punch biopsy in diagnosing leprosy among leprosy patients who were diagnosed with leprosy on clinical grounds only (i.e., number of skin lesions and/or peripheral nerve thickening). Methods: An evaluation study of diagnostic tests with a cross-sectional design was conducted at a tertiary care center of Bankura. In general, 70 new untreated leprosy patients, diagnosed solely by clinical grounds (i.e., count of skin lesions and/or thickening of the nerve) and attending the dermatology outpatient department (From February 2019 to January 2020) were enrolled in this study. After excluding pure neuritic, relapse, and seriously ill patients by consecutive sampling, they were subjected to both SSS and punch biopsy using a standard process. SPSS for Windows (Version 16.0., Chicago, SPSS Inc.) was used to analyze data. Z test, chi-square test, and kappa test were conducted to test the statistical significance between the effectiveness of SSS and punch biopsy. Results: The sensitivity, specificity, positive predictive value, negative predictive value, positive likelihood ratio, negative likelihood ratio, diagnostic odds ratio (DOR), and diagnostic accuracy of SSS were 81.81%, 95.83%, 90%, 92%, 20%, 0.19%, 102.87%, and 91.42%, respectively. Based on the results, SSS could detect acid-fast bacilli (AFB) in clinically diagnosed leprosy cases slightly less than punch biopsy, but it was statistically insignificant (Z=0.3689, P=0.71138, df=1). Finally, Cohen’s Kappa coefficient was 0.796, representing substantial agreement between SSS and punch biopsy (95% CI: 0.641-0.951). Conclusions: Overall, SSS is more or less equally effective as compared to punch biopsy in confirming leprosy cases. Interest and training on SSS among resident doctors should be emphasized accordingly.