Assessment of Various Laboratory Diagnostic Methods in Diagnosis of Cutaneous Tuberculosis. A Study from A Tertiary Care Hospital of North India

Abstract

Cutaneous tuberculosis (CTB) is the rarest case of extrapulmonary TB comprising 2% of total cases. It’s often a challenge both clinically and diagnostically. 1) To determine prevalence, age & gender-wise distribution of CTB. 2) To assess various diagnostic, microbiological modalities for the diagnosis of CTB. 76 skin biopsy specimens from suspected CTB lesions were analysed using following methods – Acid-fast Bacilli (AFB) staining (Ziehl-Neelsen method), growth of mycobacteria in culture (Lowenstein-Jensen media), and Gene Xpert MTB/RIF, Histopathological (H&E staining). Of the 76 specimens, 44 were males and 32 were females. The most commonly affected age group was 40–59 years. Infections were least common in 0-19 years age group. AFB was not seen in any of the primary smears. 10 were confirmed as CTB by the recovery of Mycobacterium in solid culture. Of the 10 culture positives, 9 were confirmed as MTB, and 1 was found to be NTM. Staining of 10 culture positive specimens revealed acid fast, beaded rods. Detection of MTB by Gene Xpert gave positive result in 9 cases with all RIF sensitive. All 9 PCR confirmed cases were also culture positive, all 9 were slow growers with a minimum of 5 weeks required for growth on the LJ slant. PCR is the test of choice and should be performed on all specimens of suspected CTB. However when coupled with the “gold standard” culture method, the diagnostic accuracy improves. Also, further, culture helps in identification and isolation of NTM’s.

Keywords

• mycobacterium
• cutaneous tuberculosis
• lupus vulgaris
• acid-fast staining
• culture
• genexpert mtb/rif