Diagnosis of cutaneous tuberculosis in biopsy specimens by PCR and southern blotting

To evaluate the use of a gene amplification and hybridisation method for detecting mycobacterial nucleic acid as a possible diagnostic method for cutaneous tuberculosis infection.

Biopsy specimens from 20 patients with various skin conditions of possible tuberculous aetiology were studied. Six patients had ulcerative nodules, seven lupiform lesions, two non-necrotic granulomas, one scrofulous lichen, one impetigo, one erythematosus lesions, one warty lesions, and one suspected tuberculous lipoma. Biopsy specimens were stained using Ziehl-Neelsen stain and cultured in Lowenstein-Jensen medium. DNA was extracted and then amplified by PCR using primers specific for the Mycobacterium tuberculosis complex. Specificity was confirmed by Southern blotting.

Of the specimens, 30% were positive for mycobacteria on staining with Ziehl-Neelsen stain, 60% were culture positive and 85% PCR positive. Only 35.2% of specimens were positive with all three techniques. A further 32.5% were both culture and PCR positive. All PCR negative samples were also negative when cultured or stained with Ziehl-Neelsen stain. Of the PCR positive specimens, 29.4% were negative when cultured or stained.

PCR, using suitable primers, is an efficient and sensitive method for the diagnosis of cutaneous tuberculosis.