Tuberculosis

Affect the lungs
1. Normal structure
  1. The right lung consists of three lobes: the superior, middle, and inferior lobes
  2. Blood Supply
    1. Pulmonary artery that arises from the pulmonary trunk and carries deoxygenated, arterial blood to the alveoli
    2. Once the blood is oxygenated, it drains from the alveoli by way of multiple pulmonary veins, which exit the lungs through the hilum
  3. The left lung consists of two lobes: the superior and inferior lobes
  4. Pyramid-shaped, paired organs that are connected to the trachea by the right and left bronchi
  5. Nervous Innervation
    1. The parasympathetic system causes bronchoconstriction, whereas the sympathetic nervous system stimulates bronchodilation
    2. Sensory nerve fibers arise from the vagus nerve, and from the second to fifth thoracic ganglia
    3. The pulmonary plexus is a region on the lung root formed by the entrance of the nerves at the hilum
Caused by
1. Mycobacterium tuberculosis
  1. Types of Mycobacteria
Epidemiology
1. In 2017, 10 million people fell ill with TB, and 1.6 million died from the disease (including 0.3 million among people with HIV)
2. Globally, TB incidence is falling at about 2% per year. This needs to accelerate to a 4–5% annual decline to reach the 2020 milestones of the End TB Strategy
3. An estimated 54 million lives were saved through TB diagnosis and treatment between 2000 and 2017
Transmission
1. Airborne, ingestion, touch
Risk factors
1. Recently infected with TB
2. Medical conditions that weaken the immune system
  1. HIV infection / Substance abuse / Silicosis / Diabetes mellitus / Severe kidney disease / Low body weight / Organ transplants / Head and neck cancer / Corticosteroids or organ transplant / Crohn’s disease
Signs and symptoms
1. Cough
  1. Causes of productive cough
2. Fever
  1. Mechanism of fever
    1. Pyrogen > Macrophages and immune cells are activated > IL-1, IL-6, IL-8, TNF-a, interferon gamma > Laminae terminalis > Pre-optic region > Posterior hypothalamic region > Activate phospholipase > Induce the production of prostaglandins E2 > Prostaglandins E2 will change the temperature set point > Peripheral vasoconstriction > Norepinephirne increases thermogenesis in adipose tissue > Shivering
3. Weight loss
4. Blood stained sputum
5. Night sweats
Investigations
1. History and physical examinations
2. CBC
3. Kidney and liver function tests
4. Inflammatory markers and (ESR)
5. CSF
6. Biopsies or mediastinoscopy
7. Histological examinations
8. Chest X-rays, CT scan, MRI
  1. X-ray
    1. Typical Post-Primary)
    2. Atypical (Primary)
9. Laboratory diagnosis
  1. Starts with the collection of a specimen
    1. Early morning sputum / Bronchoalveolar lavage / Gastric aspirate / CSF / Lymph node biopsy or aspirates / Other tissue biopsies
  2. Microscopy
    1. Ziehl Neelsen Staining / Acid Fast Staining (Specificity of 98% / Low sensitivity < 50% / Qualitative and quantitative)
    2. Fluorescent staining (Auramine-Rhodamine Fluorochrome) (Rapid and more sensitive / Expensive / Dye toxicity)
  3. Culture (The Gold Standard)
    1. Solid Media: Agar based (Middlebrook 7H10) / Egg based (Löwenstein-Jensen medium) / Culture is incubated at 35 C, 5-10%, CO2 and in high humidity. It takes 4-8 weeks / can be reported negative after 8 weeks / Rough, tough and buff colonies
    2. Liquid Media: BACTEC 460 / Mycobacteria Growth Indicator Tube (MGIT) / Positive in 2-3 weeks / can be reported negative after 6 weeks
    3. Radiometric culture has faster results (3-4 days)
  4. Molecular Methods
    1. PCR / Molecular Line Probe Assays (LPA): DNA-based diagnostic test that identifies multidrug-resistant TB (MDR TB) / Xpert MTB/RIF Assays: new NAAT that quickly identifies possible rifampicin resistance
  5. Tuberculin Test (Mantoux tuberculin skin test)
    1. Injecting tuberculin intradermally, which contains purified protein derivative from mycobacteria tuberculosis (PPD tuberculin) / Induration measured after 48-72 hours
      1. A positive test indicates the exposer to a mycobacterium / It can be positive in case of active TB (disease), people with latent infections, and people who had received BCG vaccination / A positive test in people with normal immune system will be a 10 mm induration after 48-72 hours
  6. Serology
    1. Interferon-Gamma Release Assays (IGRAs)
      1. Measures the person’s immune reactivity to mycobacteria tuberculosis / Test that detects IFN-g that is released by WBC when mixed with antigens derived from M. tuberculosis / The results within 24 hours / BCG vaccination does not cause a false positive IGRA test result
10. Of TB Contacts
  1. Assessment of the person's health / skin test / Contacts with skin test reaction of an induration diameter of >5 mm or with any symptoms of TB disease > diagnostic tests > chest radiograph / Specimen collection from sputum depends on the case and not recommended for healthy contacts with normal chest radiographs / Contacts with susceptibility to TB > examination and diagnostic testing > regardless of whether they have a positive skin test result or are ill
A Notifiable disease
1. Other notifiable diseases (UAE)
Pathogenesis
2. Histology
Management
1. Approach Considerations
  1. Isolate / Negative pressure / Masks / Continue isolation until sputum smears are negative for 3 consecutive determinations
    1. Airborne precautions
      1. Masks and Respirators
        N95 Respirator / Powered Air-Purifying Respirator (PAPR)
2. Drugs
  1. Isoniazid, rifampin, pyrazinamide, and ethambutol for 2 months ( Initial phase) / Isoniazid and rifampin for 4 more months (Continuation phase)
    1. Pyrazinamide > Serum uric acid assessments / Ethambutol > Visual acuity and red-green color perception testing (Ishihara test) for color blindness
3. Evaluating response to treatment
  1. Clinical evaluation / Bacteriological examination / Chest radiograph
BCG vaccine
1. Bacille Calmette-Guerin vaccine contains a live but very weakened form of a bacteria called Mycobacterium bovis
  1. Not given to immunocompromised people and pregnant
Complications
1. Extra pulmonary TB
  1. CNS (Meningitis) / Lymphatics (Scrofula / Pleura (Tuberculosis pleurisy) / Disseminated (Miliary TB) / Bones and joints of spine (Pott’s disease) / Genitourinary ( Urogenital TB)
Prognosis
1. If treated (Excellent prognosis) / If not treated (Mortality rate > 50%)

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Tuberculosis

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	Created by Moza Almualla about 5 years ago