title: Diagnosing leprosy: revisiting the role of the slit-skin smear with critical analysis of the applicability of polymerase chain reaction in diagnosis.
abstract: BACKGROUND
  Diagnosing leprosy is challenging, especially in early-stage cases, and the need for a sensitive diagnostic tool is urgent. Polymerase chain reaction (PCR) holds promise as a simple and sensitive diagnostic tool, but its usefulness in the Indian context requires further evaluation. Slit-skin smear (SSS) remains the conventional method of leprosy detection. Hence, this study was undertaken to evaluate and compare the diagnostic efficacy of PCR versus that of SSS.
  
  
  METHODS
  Punch biopsy of skin and SSS were obtained from the active margins of lesions. Cases were clinically grouped according to whether they were multibacillary (MB) or paucibacillary (PB) and classified into tuberculoid (TT), borderline tuberculoid (BT), borderline lepromatous (BL), lepromatous (LL), histoid, and indeterminate groups after clinicopathological correlation. DNA was extracted from biopsy specimens, and multiplex PCR was carried out incorporating primers intended for the amplification of a specific 372-bp fragment of a repetitive sequence of Mycobacterium leprae DNA.
  
  
  RESULTS
  Among 164 patients, PCR was positive in 82.3%. The sensitivity of PCR was significantly greater (P < 0.0001) than that of SSS in both the MB (85.9% vs. 59.8%) and PB (75.4% vs. 1.8%) subgroups; the difference in sensitivity in the PB subgroup is remarkable. Positivity by PCR and SSS was found in 100% of LL and histoid leprosy, but PCR had significantly greater (P < 0.0001) positivity in BT leprosy and was of definite increased value in indeterminate and TT leprosy.
  
  
  CONCLUSIONS
  Polymerase chain reaction had higher sensitivity compared with SSS, especially in diagnostically challenging and PB cases. Thus, the use of this costly but sensitive tool should be restricted to this subgroup, because SSS is sufficiently sensitive in the diagnosis of LL and histoid leprosy.
authors.affiliation: Department of Biochemistry, Institute of Postgraduate Medical Education and Research, Medical College, Kolkata, West Bengal, India.
authors.forename: Surajita
authors.initials: S
authors.lastname: Banerjee
authors.forename: Nibir
authors.initials: N
authors.lastname: Biswas
authors.forename: Nilay
authors.initials: N
authors.lastname: Kanti Das
authors.forename: Amrita
authors.initials: A
authors.lastname: Sil
authors.forename: Pramit
authors.initials: P
authors.lastname: Ghosh
authors.forename: Abu Hena
authors.initials: AH
authors.lastname: Hasanoor Raja
authors.forename: Sarbani
authors.initials: S
authors.lastname: Dasgupta
authors.forename: Pijush
authors.initials: P
authors.lastname: Kanti Datta
authors.forename: Basudev
authors.initials: B
authors.lastname: Bhattacharya
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001706:Biopsy; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007918:Leprosy / Q000175:diagnosis* / Q000382:microbiology / Q000473:pathology; D008297:Male; D008875:Middle Aged; D009166:Mycobacterium leprae / Q000235:genetics / Q000302:isolation & purification*; D016133:Polymerase Chain Reaction / Q000379:methods*; D012680:Sensitivity and Specificity; D055815:Young Adult