Erythema induratum associated with tuberculous lymphadenitis: analysis of a case using polymerase chain reactions with different primer pairs to differentiate bacille Calmette-Guérin (BCG) from virulent strains of Mycobacterium tuberculosis complex.

We retrospectively analyzed a bacille Calmette-Guérin (BCG) vaccinated female patient who developed erythema induratum in association with tuberculous lymphadenitis. The polymerase chain reaction (PCR) with two pairs of primers was performed. Only one pair was able to detect the myocobacterial DNA from the paraffin-embedded specimen of the erythema induratum (EI) lesion. However, both pairs showed positive results with the tuberculous lymphadenitis specimen. Sequence analysis of the PCR products excluded the possibility of BCG as the potential pathogen. Both lesions responded favorably to antituberculous therapy. Our study attests to the tuberculous nature of EI and demonstrates that BCG vaccination per se does not induce the lesion or interfere with the PCR result. Finally, using at least two pairs of primers targeting different genomic segments and possessing species-identification capability may raise the detection rates and solve some controversies about the nature of tuberculids.