RESUMEN
Cutaneous tuberculosis presents a diagnostic challenge, as it is difficult to demonstrate the causative organism by histopathology and also culture of organisms from skin lesions is a less rewarding and time consuming process. Aim: Present study was undertaken to evaluate the utility of immuno-histochemical staining to demonstrate Mycobacterium tuberculosis antigen in tissue sections. This is based on the finding that the mycobacterial antigen is the last to disappear from the tissues and thus can be used as a marker of mycobacterial infections. Material & Methods: Fifty randomly selected skin biopsy specimens were subjected to routine histopathological examination to corroborate the clinical diagnosis. Immuno-histochemical study was undertaken to demonstrate mycobacterial antigen. Observations: All the tissue sections were negative for AFB, both by Z-N stain and by culture. Mycobacterial antigen was demonstrable in 68% of cases of cutaneous tuberculosis. The highest positivity was recorded in scrofuloderma (89%), followed by Lupus Vulgaris (69%) and Tuberculosis Verrucosa Cutis (47%). Conclusions: Mycobacterial antigen was demonstrable in majority of cases of cutaneous tuberculosis using polyclonal antiserum. However, since cross reactivity was reported in cases of leprosy and also in some fungal infections, this test by itself cannot be considered as diagnostic. The results should be considered along with other findings.