Pathological Diagnosis of Bone and Joint Infections

Bone and joint infection (BJI) is a major global health burden with significant management challenge. BJI can be divided into suppurative (mainly bacterial infection), granulomatous (e.g., tuberculosis and fungal infection), and parasitic infection. Although isolating the pathogen from tissues is the gold standard for the confirmation of BJI, pathological examination performs a major role in the diagnosis of BJI. An invasive sampling is often required for several reasons including the distinction between infectious from non-infectious diseases. The inflammatory response to pathogenic microorganisms is sufficiently consistent to allow pathologists to diagnose an infectious process and to suggest the causative agent. For example, epithelioid cell granulomas associated with caseous necrosis are highly suggestive of tuberculosis, and the diagnosis can be retained with confidence even if bacteriological investigations are lacking or negative. Although necrotizing granuloma is highly suggestive of tuberculosis, it must be kept in mind that fungal infections and bacteria such as Brucella spp. may also cause necrotizing granulomas. The identification of the infectious agent such fungi or parasite allows establishing the etiological diagnosis of BJI. Ancillary techniques: special stains, immunochemistry, and molecular assays may help identify infectious agent in tissue sections.