A 28-year-old woman with a history of pulmonary tuberculosis now presents with spinal deformity and kyphosis. Which is the most common organism responsible for tuberculosis of the spine?

Explanation

## Causative Organism of Pott Disease **Key Point:** *Mycobacterium tuberculosis* (human strain) is the causative organism in >95% of spinal tuberculosis cases worldwide, including in India. ### Mycobacterial Species in Spinal TB | Organism | Frequency in Pott Disease | Source | Clinical Notes | |---|---|---|---| | **M. tuberculosis (human)** | >95% | Human-to-human transmission | Standard TB; most common | | **M. bovis** | <5% | Unpasteurized dairy, cattle contact | Rare; associated with zoonotic exposure | | **M. marinum** | <1% | Aquatic environments | Skin/soft tissue primarily; spinal involvement exceptional | | **M. avium complex** | <1% | Immunocompromised (HIV/AIDS) | Opportunistic; rare in immunocompetent | ### Epidemiological Context **High-Yield:** In endemic TB regions like India, the overwhelming majority of Pott disease cases arise from reactivation of latent TB or progressive primary TB involving the lungs, with hematogenous dissemination to the spine. The human strain is transmitted via respiratory droplets and is the dominant pathogen. ### Pathogenesis **Clinical Pearl:** Spinal TB typically develops through: 1. Primary pulmonary TB infection 2. Hematogenous dissemination (often years later) 3. Seeding of vertebral metaphysis 4. Progressive vertebral body destruction and kyphotic deformity **Mnemonic:** **MTB-H** = *Mycobacterium tuberculosis* — **H**uman strain — responsible for >95% of Pott disease. **Warning:** Do not confuse M. bovis (from unpasteurized milk) with the human strain. While M. bovis can cause TB, it is rare in spinal disease and is associated with specific epidemiological exposure (cattle farming, unpasteurized dairy consumption). [cite:Harrison's Principles of Internal Medicine 21e Ch 205]