10+ Year Member
7+ Year Member
Feb 28, 2008
Resident [Any Field]
Quick question regarding extrapulmonary TB and I hope someone can clear this up for me.

So my current understanding is extrapulmonary TB is often found simultaneously with secondary (reactivation) pulmonary TB, but extrapulmonary TB is itself classified as primary TB.

So after initial infection, the Mycobacteria may disseminate and lie dormant in the organs, bones, and CNS. Later on, they may become reactivated (still classified as primary TB). At the same time, Mycobacteria in the lungs may become reactivated (secondary TB).

Is my understanding of the classification of primary and secondary TB correct or am I wrong somewhere?

One more question: can extrapulmonary TB come from secondary reactivation (or reinfection) TB? My current understanding is that all extrapulmonary TB is from seeded Mycobacteria present in the initial infection/Ghon complex, but I can't think of any good reason why the upper lobe caseous cavitary lesion in secondary TB couldn't seed extrapulmonary infection.


Renowned Wolf
10+ Year Member
Mar 12, 2009
Philadelphia, PA
Medical Student
You're correct that extra-pulmonary TB can arise from both primary and secondary TB. TB is spread by what blood and lymph right? So there is no reason why both primary and secondary infections can't spread the organism via these routes.

I'm not sure about if extra-pulmonary TB is classified as primary or secondary.

Don't forget there is also miliary TB which is really presence of TB infections in several organs simultaneously. On the other hand, extra-pulmonary TB is usually in one site.