A rare case of long-standing lupus vulgaris with psoriasiform manifestations diagnosed by mNGS: a case report.

This report describes a rare case of lupus vulgaris mimicking psoriasis, undiagnosed for over 40 years. Conventional diagnostics, including histopathology and mycobacterial culture, failed to yield a definitive diagnosis. Ultimately, metagenomic next-generation sequencing (mNGS) of the skin tissue detected the Mycobacterium tuberculosis complex, confirming the infection. The patient showed marked clinical improvement following two months of dual-drug anti-tuberculosis therapy. This case highlights the clinical utility of mNGS for diagnosing atypical, long-standing cutaneous tuberculosis when conventional methods are negative, thereby preventing prolonged misdiagnosis and ensuring timely treatment.