Pathology of Bone and Joint Tuberculosis

Although isolation of the mycobacterial agent from the infected tissues is the gold standard for the definitive diagnosis of tuberculosis, histopathological examination of bone and joint tissues allows establishing the diagnosis of tuberculosis, especially if bacteriology is not available or fails to identify the causative agent. Typically, tuberculosis is characterized by necrotizing granulomas, which represent tissue reactions that arise in the presence of tubercle bacilli and are sufficiently characteristic of tuberculosis. But pathologists must be aware that the introduction of tubercle bacilli into a tissue elicits a spectrum of inflammatory reactions and granulomatous and necrotic lesions may be also elicited by other infective organisms, such as non-tuberculous mycobacteria, Brucella spp., and fungal species. Non-infectious conditions such as sarcoidosis can also mimic tuberculous lesions. Pathologists also must be aware of atypical forms of tuberculosis such as suppurative forms seen in acute or reactivation phases and fibrotic forms seen in late phases. Ancillary techniques used on histological sections, particularly special stains for acid-fast bacilli, may help confirm the diagnosis of tuberculosis. However, these stains are often negative in osteoarticular tuberculosis due to the scarcity of tubercular bacilli in this form of tuberculosis. Nucleic acid amplification tests in formalin-fixed embedded tissues may help establish the diagnosis of tuberculosis, especially in cases without available bacteriology.