Cutaneous tuberculosis is an ancient disease. Cutaneous lesions of TB were described long before Robert Koch identified Mycobacterium tuberculosis. The first description of cutaneous TB is attributed to Laennec⁶ in 1826 who described his own prosector’s wart that followed an injury sustained while carrying out an autopsy on a patient with spinal TB. Mycobacterium tuberculosis was first demonstrated in tissue sections of lupus vulgaris by Demme⁷ in 1883. In 1886, Reihl and Paltauf⁸ established that the prosector’s wart was a TB lesion. Apple-jelly nodules in lupus vulgaris were first described in 1888⁹ and tuberculids in 1896¹⁰.

Table (1):
Confirmed Cutaneous TB positive cases.

Cutaneous TB appears to have been frequently encountered all around the world during the early part of this century and comprised 0.1 to 2.6 per cent of the total number of dermatology patients in various hospitals at different periods of time^11-17.

In India, Cutaneous TB accounts for 0.11 to 2.5 per cent of all patients with skin diseases seen at hospitals located in different parts and this figure seems to be constant for all regions of the country^18-22. In a study from Vishakhapatnam¹⁸, cutaneous TB constituted 0.025 per cent of all patients with TB and 15 per cent of all patients with extra-pulmonary TB. One study²² found that cutaneous TB was associated with TB in other organs in 22.1 per cent of patients.

Table (2):
Types of Mycobacterium recovered from positive samples.

Cutaneous TB is not a well-defined entity but encompasses an extensive range of clinical manifestations²³. Because of this extensive range of manifestations coupled with the rarity of the disease, a high index of clinical suspicion is required to identify skin lesions that could possibly be tubercular in origin and therefore will require Mycobacteriological evaluation. Histopathology many a times shows non-specific inflammation without granuloma formation²⁵. The presentation is determined by the host immune response, the route of inoculation and the previous sensitization of the host to the Mycobacterium tuberculosis²⁴. Cutaneous tuberculosis is classified according to the source of infection²⁵ [Table 5] as; Clinical presentation varies from an ulcer to multiple plaques, papules, pustules, nodules, warts, sinus tracts and soft tissue abscesses (Image 1 showing clinical presentation of a patient in our hospital). Lupus vulgaris is the most commonly reported type from India and globally followed by TB verrucosa cutis and scrofuloderma. In our study, the most common variety was Lupus vulgaris (n=06) followed by scrofuloderma (n=03) and TB verrucosa cutis (n=01) [Table 4]. The other types are distinctly rare. The lesions of Lupus vulgaris routinely appear as “Apple jelly” nodules on diascopy and are most frequently found on the face and neck²⁶.

Table (3):
Age and gender-wise distribution of patients with suspected lesions.

Our study group consisted of skin biopsy specimens diagnosed as Cutaneous TB after microbiological evaluation.

Histopathology of skin biopsy specimens, demonstrates the characteristic features (well-formed granulomas with absence of caseous necrosis, granulomas with caseous necrosis, and the presence of poorly formed granulomas with intense caseous necrosis) [Image 3 showing a granuloma in a H&E stained skin biopsy specimen). Khandka, P et al. in their study, Cutaneous Tuberculosis: Clinicopathologic Arrays and Diagnostic Challenges proposed that, the equivocal manifestation of cutaneous tuberculosis to correlate the histologic with clinical observations in an evidence-based diagnosis is imperfect and lacking pragmatics²⁷.

Table (4):
Clinical variants and Laboratory data of samples.

AFB: Acid fast bacilli

AFB smear microscopy still remains a fast, simple, and cost-effective technique for the early diagnosis and assessment of treatment response in most countries globally. But its limitations remain overall low and variable sensitivity and the inability to differentiate between Mycobacterium tuberculosis and non-tuberculous mycobacteria²⁸. Also, a minimum of 10,000 (10⁴) Bacilli/ml of a specimen are required for the smear to be positive^29,30. In our study, none of the smear was positive for AFB.

Table (5):
Classification of cutaneous TB (According to the source of infection).

Culturing the specimen for the diagnosis of TB is still considered as a “gold standard” method. It has very high sensitivity and can detect as few as 10 Bacilli/ml of a specimen, making it an excellent modality for the isolation of MTB from paucibacillary specimens, as is the case with cutaneous TB and other EPTB samples. But due to slow the generation time of MTB (15-20 hrs) culturing MTB can take 4-8 weeks to yield results, which not only delays diagnosis but also the treatment in many cases^31,32. Khandka, P et al. in their study, observed that, the cultures of the pathogen, Mycobacterium tuberculosis, on specific solid media or by automatic detection of its metabolites in liquid media remain the gold standard method, for identification and their drug sensitivities²⁷. In our study, of the 76 skin biopsy specimens with suspected CTB, 10 (16.6%) were found confirmed as CTB by the recovery of Mycobacterium in solid culture (LJ media). Of the 10 culture-positive cases, 9 (90%) were confirmed as Mycobacterium tuberculosis, and 1 (10%) was found to be Non-tuberculous mycobacteria (NTM).

Table (6):
Different diagnostic modalities used.

Although the standard culture media need a long time for the growth of Mycobacterium tuberculosis, more rapid liquid culture based methods have been developed²⁸. The rapid automated, culture techniques widely used include the radiometric BACTEC 460 TB system and the non-radiometric BACTEC MGIT 960 system which can detect growth in as early as 3–7 days, BacT/ALERT MB which can detect growth as short as 9-14 days^33,34.

Conventional techniques for the diagnosis of CTB have various limitations. Difficult clinical diagnosis and a paucibacillary nature of the lesion act as added roadblocks. This has led to discovery and subsequent use of newer molecular techniques for the diagnosis. DNA PCR based techniques have been recommended for the diagnosis of various forms of CTB, but it has a variable sensitivity³⁵. One of them commonly used worldwide, the Gene Xpert MTB/RIF. The GeneXpert MTB/RIF assay is a rapid, fully automated molecular assay with good sensitivity for CTB specimens, this assay has become a popular point of care choice for the early and accurate diagnosis of CTB. The rapidity of results (within 2 hours) combined with good sensitivity for EPTB specimens has led to incorporation of this test into routine diagnostic algorithms in India and world over. The test also provides Rifampicin sensitivity results subsequently. In PCR reactions, discrete fragments of DNA are specifically amplified from specimens in CTB³⁶. As few as 130 Bacilli per ml of specimen can be successfully detected by the advanced molecular technique and results can be had in under 2 hours³². The GeneXpert MTB/RIF assay was applied to all suspected CTB specimens received by our lab in this study.

The GeneXpert MTB/RIF assay detects the MTB complex DNA and RIF resistance. This is achieved by the amplification of the 81 bp fragment of the MTB rpoB gene and subsequent probing of this region for mutations that are associated with resistance to rifampicin. Five probes (A-E) are used for the detection of MTB complex DNA. This assay can be completed in less than 2 hrs. It incorporates a considerable number of sequences of the mycobacterial genome (IS6110, IS986, 65 kDa, and 38 kDa) for detection of MTB complex and the RIF resistance-determining region³⁴.

However even PCR has few limitations, of particular importance is the reduced sensitivity of the assay, as may be seen with inappropriate specimen collection, processing (loss of DNS during extraction), transport and presence of inhibitory substances³⁷.

The performance of the Xpert MTB/RIF assay when compared with the IS6110‑based RT‑PCR assay for MTB detection in extra-pulmonary tuberculosis specimens was found to exhibit better sensitivity³⁸. Tortoli et al. studied the utility of Xpert MTB/RIF assay in 1476 extra-pulmonary tuberculosis specimens and found it 81.3% sensitive and 99.8% specific³⁹. A systematic review reported that Xpert MTB/RIF assay accurately detected the majority of non-respiratory samples testing smear-positive and culture-positive for Mycobacterium tuberculosis, but only two-thirds of smear-negative samples⁴⁰. Qadri, M et al. in their case report about a culture negative cutaneous TB case observed that, due to the different type of lesions, correct diagnosis may be delayed because investigations fail to detect TB, as in our case where cultures were negative and TB was only detected by GeneXpert⁴¹. The ten PCR positive skin biopsy samples in our study were all culture-positive on solid LJ media.

This comprehensive study has given us a clear insight into the pattern and extend of CTB in this region. Our study in all likelihood is the first of its kind from the Kashmir region (Northern India) describing the prevalence, distribution, variants, and diagnostic modalities available for the optimum detection and recovery of the Mycobacterium in all suspected skin lesion samples.