Tuberculous Arthritis Diagnosed by Metagenomic Sequencing after Negative Microbiology Studies and a 4-Year Delay

Tuberculous arthritis of the knee is a rare form of extrapulmonary tuberculosis that often presents with nonspecific symptoms, leading to delayed or missed diagnosis, particularly in elderly patients with comorbidities. We report the case of a 70-year-old man with a 2-year history of left knee pain and recurrent swelling. The patient was under therapy for lung cancer. He underwent two arthroscopic procedures for both diagnostic and therapeutic purposes. Repeated standard tests for tuberculosis were negative before metagenomic next-generation sequencing (mNGS) identified Mycobacterium tuberculosis nearly 2 years later. After 1-year triple-antituberculous therapy, he remained asymptomatic at the 2-year follow-up. This case highlights a high index of suspicion for indolent infection in culture-negative chronic arthropathy. The use of mNGS-increasingly accessible and cost effective-enables rapid and sensitive diagnosis of paucibacillary extrapulmonary tuberculosis.