Pathogenesis of TB:

• An infected individual releases droplets containing tubercle bacilli, that are inhaled by a healthy individual. These droplets then travel to the alveoli present in lungs.

• In the alveoli, tubercles multiply in number. Some tubercles may enter the bloodstream and travel to different parts of the body such as brain, larynx, spine, bone, kidney, etc.

• Within 2 to 8 weeks of infection, macrophages are activated in the alveoli which start engulfing the tubercle bacilli. Many such macrophages form Granuloma (called Gohn Focus), a shield or barrier which contains the bacilli from multiplying. (Latent Tuberculosis Infection)

• If the immune system fails to keep the bacteria under control, the bacteria start to multiply rapidly, causing TB disease.

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Extrapulmonary TB:

• The above described process can occur in any part of the body.

• Miliary TB: Characterized by spots all over the body or found in a specific organ. Mostly occurs in children younger than 5 years of age.

• Potts's Disease: Occurs when TB infection of spine reaches to the spinal ligaments.

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Sources: 

https://www.cdc.gov/tb/education/corecurr/pdf/chapter2.pdf

https://www.jotscroll.com/forums/11/posts/156/extrapulmonary-tuberculosis-tb-symptoms-types-diagnosis-treatment.html

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