Tuberculosis for USMLE Step 1 and USMLE Step 2

Handwritten video lecture on Tuberculosis for USMLE Step 1 and USMLE Step 2. Reviewing Pathogenesis, Signs and Symptoms, Investigations, and Treatment.

BACTERIOLOGY
Tuberculosis (TB) is caused by mycobacterium tuberculosis with its main virulence factor is due to its mycolic acid coat that increases immune resistance but the bacteria grows much slower. Ziehl-Neelson staining aka Acid Fast stain can stain tuberculosis, but also stains nocardia, legionella, isospora, and cryptosporidium. Tuberculosis (TB) bacteria is also aerobic.

PATHOGENESIS
EXPOSURE – Tuberculosis (TB) bacteria must first go into the lower respiratory tract. Generally prefers upper part of the middle and lower lobe leading to primary tuberculosis infection.
MACROPHAGE – undergoes phagocytosis by macrophage and the tuberculosis will be inside of phagosome. Normally the lysosome needs to fuse to form phagolysosome. This can be inhibited by tuberculosis bacteria so over time the mycobacterium grows within the phagosome until rupture. Eventually the macrophage will rupture which will then be taken up by macrophages again.
GRANULOMA – Granuloma formed when the number of macrophages with mycobacterium increases. With Cell Mediated Immunity (CMI) activation by T cells release lymphokines that activate macrophages which kills the Tuberculosis (TB) and creates casseous necrosis in the central area. Many of the tuberculosis (TB) bacteria are not killed and remain dormant.

SYMPTOMS
Range from asymptomatic to fever, pleuritic and chest pain. Erythema nodosum, phlyctenuclar conjunctivitis may also be seen. Early there is non-purulent cough that may become plurulent with blood. May also have pleuritic chest pain with dyspnea and respiratory distress.
GHON FOCUS – ghon focus is an actual lesion that is found in the peripheral part of the lung. After some time may travel to hilar lymph node forming the ghon complex.
DORMANT – There is granuloma formation which has live tuberculosis (TB) bacteria. This may reactivate and is known as reactivation TB, Post primary TB, or Secondary TB. Reactivation occurs when the patient later becomes immunocompromised. Location is in upper/posterior lobe because of increased oxygen found.
PROGRESS – Tuberculosis (TB) grows and creates cavity that enlarges. Goes to airways and patient is infectious. If goes to pleura may cause pleural effusion. Hilar lymphadenopathy that may press on trachea. May go to blood vessels and create disseminated tuberculosis.
COURSE – galloping consumption is when it becomes very severe. Consumption is when it takes a chronic course and finally spontaneous remission.

DIAGNOSIS
CHEST X-RAY – May see cavitation, Ghon complex, and calcified nodule
Acid Fast Bacilli (AFB) Microscopy – Done with sputum sample or bronchioalveolar lavage (BAL). Gastric can give high false positive with Ziehl Neelsen Stain
CULTURE – With Lowenstein Jensen, but takes 4-8 weeks to grow.
MOLECULAR TESTS- Include nucleic acid amplification, PCR, MTB and RIF.
TUBERCULIN SKIN TEST (PPD) – May detect latent stage, however, many false negatives and false positive.

TREATMENT
INITIAL PHASE (2 MONTHS) – attempting the kill as much bacteria as possible
CONTINUATION PHASE (2-6 MONTHS) – kille persistent and resistant bacteria.
Isoniazid and Rifampicin is used for 6 months. Pyrazinamide and Ethambutol is used only in first 2 months of treatment.
Must monitor sputum with culture and by 3 months must be culture negative. If persistent than may be bacterial resistance or there is decreased comlaince. Also monitor Drug Toxicity which is unique for each drug. Monitor liver function test, uric acid levels, B6 levels, and optic neuritis.
Direct Observation Treatment (DOT) – helped with compliance with nurse observing patient take the drug.
If there is resistance can add fluoroquinolone, streptomycin, amikacin, kanamycin, capromycin. If resistant to isoniazid and rifampicin then increase treatment to 9 months. Do this also if there is cavitary lesion. Multdrug resistant Tuberculosis (TB) (MDR) you should add Fluoroquinolone and other second line drug. XDR is if there is resistance to first and second line drug.

[mohammmedahmedali]

جزاكم الله خيراً - May Allah reward you
continue

[parisad]

Thanks god for existence of such very well educated and informed physicians like you!!!

[Star-ghir]

6 years later
Thank you this is still helpful ❤️❤️

[hadjerbough]

Awesome lecture nd amazing explanation .. Thanks a lot sir you helped me a lot

[peterpalme]

Very helpful. It helps me a lot in my essay writing.

[HebaHossam]

best explanation for TB I've heard so far, thank you so much

[pharmacist]

Really appreciated sir and waiting for more such videos

[erinblue]

I got the disease, It took 4 months to discover It since I was not conagious but the bacteria went in the right lung First then migrated onto the pleura membrane, and that was very painful, also It caused the formation of a lot of liquid in the lung...my tubercolosis was dormant for more than a decade and suddendly got activated for no apprent reason...

[amjadhanna]

the t you should have mentioned the role of TNF a in preservation of the wall around the necrosis even after the macrophages are destroyed so that the M.tuberculosis wont disseminate anywhere, it is super important, as it is pro inflammatory and maintain the response around the necrosis area

[IM.MEDICAL]

Very well explained indeed. Thank you for this video!

[SF-yhot]

What kind of chemical signal does the mycobacterium release that inhibits the fusion of lysosome and phagosome?

[fatimahassan]

thankyou so much ! this cleared alot of my concepts

[AimanM]

Such an awesome lecture. Much much thanks! :D

[amjadhanna]

actually the "T cells comes to kill the macrophages" part gives me doubt

[thebookdoc.writing.and.editing]

I understood this before I watched it and the presentation is, I guess, exactly as I understand it. One question. When mentioning terms that make things sound smarter, like "necrosis" why not just say. "You have cell necrosis, **or cell death**"? it is not just medicine but every damned science that thinks speaking in latin makes them have exclusive knowledge when it is actually something really fucking simple. I'm not more impressed with cell death when it is 'necrosis', and all it does is exclude people, normal people who eat ice cream, from understanding what the fuck you are talking about.

[mareeduraviteja]

Just be more audible...ur voice is very feeble, even when played at full volume... correct ur sound clarity