Tuberculosis (TB)

Study Guide ​

Introduction: 

  • Caused by Mycobacterium tuberculosis, an acid-fast bacillus.

  • TB is acquired by inhalation of respiratory droplets spread by coughing.

  • Previous BCG vaccine has no impact or effect on recommendations for treatment.

  • Primary TB is seen with the initial exposure.

  • Secondary TB is the reactivation of a latent infection.

Epidemiology:

  • TB affects approximately 1/3 of the world’s population.

  • TB is the world’s 2nd most common cause of death from infectious disease after HIV/AIDS.

  • Saudi Arabia is considered as a moderate burden country. 

 

 

Risk Factors:

Approximately all patients with TB have one or more of the following risk factors:

  • Recent immigrants (in the past 5 years from endemic area).

  • Prisoners

  • HIV positive

  • Healthcare workers

  • Close contact with TB patient

  • Steroids use

  • Alcoholics

  • Hematological malignancies

  • Diabetes mellitus

Clinical Presentation:

Primary TB: 

  • With the initial exposure.

  • The bacilli are inhaled and deposit in the lungs as Ghon’s complex (dormant).

  • Focal caseating necrosis in the lower lung lobes and hilar lymph nodes on pathology.

  • Usually asymptomatic patient, sometimes pleural effusion.

  • Positive PPD screening test.

Secondary TB: 

  • Reactivation of the TB due to immune suppression like in AIDS and sometimes aging.

  • Occurs in the lung apex due to high O2.

  • Symptomatic patient: fever, night sweats, cough with hemoptysis, and weight loss.

  • Biopsy will reveal caseating granulomas.

  • Can lead to miliary extrapulmonary TB (systemic dissemination through lymphatic or blood):

    • Seen in 20% of HIV seropositive patients.

      1. Sterile pyuria.

      2. Meningitis in the base of the brain.

      3. Cold abscess in the cervical lymph nodes.

      4. Pott disease in the lumbar vertebrae.

Hemoptysis

suggests advanced TB. 

The most common organ to be involved in miliary TB is the kidney. 

Diagnosis:

Chest X-ray:

Best initial test.

  • Cavitary lesion in the upper lobes.

Sputum acid-fast testing:

  • Definitive diagnosis.

  • Obtain morning sputum.

Pleural biopsy:

  • Most accurate diagnostic test.

  • Invasive, not used routinely.

Screening:

  • Mantoux tuberculin skin test (TST), a purified protein derivative (PPD) skin test is used.

                      What induration size is considered positive:
                             “The smaller the higher the risk”

>5 mm

  • HIV positive

  • Glucocorticoids users

  • Close contact with active TB patient

  • Organ transplant patients

  • Abnormal calcifications on CXR

>10mm

  • Recent immigration in the past 5 years

  • Healthcare workers

  • Prisoners

  • Injection drug users

  • Close contact with TB patient

  • Diabetes

  • Alcoholics

  • Hematologic malignancies


>15 mm
Healthy with no risk factors

  • False positive:

    • Due to non-tuberculosis mycobacteria infections or vaccination.

  • False negative:

    • Anergy. 

Every person with positive PPD test should have CXR: to exclude active TB 

Treatment:

Active TB:

  • RIPE Regimen: Rifampin, Isoiazide (INH), Pyrazinamide and Ethambutol.

  • 4 drug empiric therapy for 6 month:

    • In the first 2-monthsèuse all 4 drugs. 

    • For the remaining 4-monthsèuse only Refampin +Isoniazide (INH). 

  • Treatment might be extended for > 6months in some cases e.g.: osteomyelitis, pregnancy, or military TB.

  • All anti-tuberculosis drugs are hepatotoxic.

  • Steroids might be used to decrease the risk of constrictive pericarditis and meningitis.

Latent TB (only positive PPD test):

  • 9 months of INH.

DO NOT

discontinue the anti TB drugs except if LFTs are 3-5 times higher than the baseline normal for the patient. 

References:

  • Agabegi, Steven S, Elizabeth D Agabegi, and Adam C Ring. Step-Up To Medicine. Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins, 2013. Print.

  • Fischer, Conrad. Master The Boards. Print.

  • Kumar, Parveen J, and Michael L Clark. Kumar & Clark's Clinical Medicine. Print.

  • Sattar, Husain A. Fundamentals Of Pathology. Chicago: Pathoma.com, 2011. Print.

  • Jidc.org,. N.p., 2015. Web. 13 Nov. 2015.

  • Pathologystudent.com,. 'Ode To The Granuloma'. N.p., 2015. Web. 13 Nov. 2015. (Figure1).

  • Reference.medscape.com,. 'Chest X-Rays: Subtle But Key Findings You Need To Know'. N.p., 2015. Web. 13 Nov. 2015. (Figure2).

  • Pathologyoutlines.com,. 'Acid Fast / Auramine-Rhodamine'. N.p., 2015. Web. 13 Nov. 2015. (Figure3).

First author:  Abeer Khairi              
          
​Second author:  Roaa Amer      

Reviewed by:  Mneera Khaled
                                Fahad Alsayed

 Format Editor: Salman Alahmed

Audio recording:

 
- Read by: Bayan Alzomaili


- Directed by: Rana Alzahrani


- Audio production: Bayan Alzomaili

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