Respiratory: TB Flashcards
Mycobacteria are:
- gram-negative cocci shaped bacteria
- gram-postive cocci shaped bacteria
- gram-negative rod shaped bacteria
- gram-postive cocci shaped bacteria
- gram-negative spiral shaped bacteria
Mycobacteria are:
- gram-negative cocci shaped bacteria
- gram-postive cocci shaped bacteria
gram-negative rod shaped bacteria
- gram-postive rod shaped bacteria
- gram-negative spiral shaped bacteria
What are the red flag pathologies (on BMJ BP) for haemoptysis? [8]
- Pulmonary TB
- Primary lung cancer
- Lung metastasis
- Anticoagulants
- Toxic inhalation
- Mitral valve stenosis
- PE
- LVF
- Coagulopathy
- Thrombocytopenia
- Aspergilloma
- Aspiration of foreign body
Pathogenesis of TB?
- Inhaled bacteria in droplets carried into lungs:
typically settle in subpleural area mid or lower lung zones - Engulfed by alveolar macrophages form Ghon Focus
- TB laden macrophages travel to local lymph nodes
- Form Primary complex (aka Ghon Complex) = primary TB lung infection in non-immune host (Ghon Focus, TB granuloma), plus draining lymph nodes.
- 5% Ptx have primary pulmonary TB
- 5% will control TB temporarily, but it will be reactivated later (latent): post primary TB
- 90 % have no more disease progression
What is a ghon focus? [1]
What is a ghon complex? [1]
A small lung lesion known as a Ghon focus develops. The Ghon focus is composed of tubercle-laden macrophages.
The combination of a Ghon focus and hilar lymph nodes is known as a Ghon complex
Investigating for TB:
Which stain do you use for Tb? [2]
What colour do they appear when using this stain? [2]
Ziehl–Neelsen stain: bright- red colored rods when a is used.
Auramine: flourescent coloured
Investigating TB:
How do you diagnose if you’ve got latent TB or not? [2]
Tuberculin sensitivity Test – aka PPD (Purified Protein Derivative) (Manteux) test:
- Tuberculin is injected between layers of the dermis, tuberculin is a component of the bacteria, and if a person has previously been exposed to TB, the immune system reacts to the tuberculin and produces a small, localized reaction within 48 to 72 hours; if the reaction creates a large enough area of induration (rather than just redness), it’s considered to be a positive test.
DOESNT DISTINGUISH BETWEEN LATENT AND ACTIVE TB
IFN-γ assay
- If patient has had TB infection, T lymphocytes produce interferon gamma in response – measured and compared with control sample.
If a patient has suspected primary TB, which investigations would you order? [2]
Primary investigations for active pulmonary infection include:
- chest x-ray
- three sputum samples obtained for microscopy, culture, and nucleic acid amplification testing (NAAT).
Describe the three different sputum analyses used for TB investigations [3]
Sputum microscopy
- three samples are required.
- Ziehl-Neelsen stain
Culture Gold standard
- can take up to 6 weeks in solid media
- can take 1-3 weeks in liquid media
NAAT:
- amplifies a specific nucleic acid sequence that can be detected via a nucleic acid probe
- some NAATs can detect genes encoding drug resistance
Describe the two NAAT tests / assays used for TB [2]
Xpert MTB/RIF assay:
- detects M tuberculosis
- detects rifampin-resistance mutations.
Amplified Mycobacterium tuberculosis direct test:
- detects TB but NOT drug resistance.
Which form of investigating for latent TB is preferred for patients with a history of BCG vaccincation? [1]
An IGRA is preferred in individuals with a history of BCG vaccination.
The NICE guidelines on tuberculosis (2016) describe “deep cough” sputum samples. If they are not producing enough sputum, the options are what? [2]
Sputum induction with nebulised hypertonic saline
Bronchoscopy and bronchoalveolar lavage (saline is used to wash the airways and collect a sample)
Describe the clinical presentation of latent TB [1]
Latent infection of TB is asymptomatic and non-contagious
Name this sign of TB [1]
Erythema nodosum
Describe the clinical presentation of primary or reactivaed TB
Pulmonary TB:
* Dyspnoea, cough (+/- haemoptysis) , chest pain.
* Cough: over 2 to 3 weeks; initially dry, later productive.
* Chest examination: crackles, bronchial breath sounds, or maybe normal.
* Fever: usually gradual onset and low-grade.
* Night sweats: maybe drenching.
* Weight loss, anorexia, and malaise are also common.
* Erythema nodosum(tender, red nodules on the shins caused by inflammation of the subcutaneous fat)
Where is the most common extra-pulmonary site for TB? [1]
Describe how they change [3]
Lymph nodes:
* Enlarged
* Firm
* Non-tender
NB: most commonly affects cervical and supraclavicular nodes.
Describe the clinical findings on respiratory an examination for TB [4]
- Sputum pots with purulent or blood-stained sputum
- Enlarged, tender lymph nodes
- Crackles or bronchial breathing over consolidation
- Dullness to percussion and decreased fremitus over pleural effusions
State 4 differential diagnoses for pulmonary TB [4]
- Bacterial pneumonia or viral respiratory tract infection
- Interstitial lung disease
- Malignancy including lymphoma
- Sarcoidosis
Describe the cough in primary TB [1]
Cough: over 2 to 3 weeks; initially dry, later productive.
Patients with TB can present with an abscess. Describe the nature of this abcsess [3]
A cold abscess:
- a firm, painless abscess
- usually in the neck.
- They do NOT have the inflammation, redness and pain you expect from an acutely infected abscess.
Describe 3 groups for risk factors for TB reactivation?
Immunocompromised states:
- infection with HIV
- Diabetes mellitus
- Silicosis
- Malnutririon
- Ageing
- Prolonged therapy with corticosteroids
- Other immunosuppressive therapy
- Organ transplant
Substance abuse
- IV
- Alchoholics
Others:
* Tumor necrosis factor- alpha [TNF-α] antagonists (used in RA)
* Haematological malignancy
* Severe kidney disease /haemodialysis
Treatment of which drug type is a risk factor for TB re-activation?
Prolonged therapy of corticosteroids
Explain the pathology of primary TB
Primary TB:
- After exposure macrophages ingest the bacteria, they produce a protein that inhibits fusion of macrophage and lysosome, which allows the mycobacterium to survive
- Proliferates, and creates a localized infection.
- About 3 weeks after initial infection, cell-mediated immunity kicks in, and immune cells surround the site of TB infection, creating a granuloma, essentially an attempt to wall off the bacteria and prevent it from spreading.
- The tissue inside the middle dies as a result, a process referred to as caseous necrosis, which means “cheese-like” necrosis, since the dead tissue is soft, white, and looks a bit like cheese. This area is known as a “Ghon focus.
Would would CXR of Ptx with TB present like? [3]
Apex of the lung often involved (more aerobic!)
Ill defined patchy consolidation
Cavitation usually develops within consolidation
Healing results in fibrosis
Hilar lymphadenopathy
Which type of TB is depicted? [1]
Miliary TB
Which type of TB is depicted? [1]
Tuberculosis, post-primary. There are large cavities in both apices and smaller cavities scattered throughout the lungs. The lungs are over-aerated and there is already scarring present. Dilated bronchi (tuberculous bronchiectasis) is present throughout the lungs.
A 26-year-old male presents to the General Practitioner with anorexia, loss of appetite, hot flushes, especially at night and weight loss for the past six months. He has had a cough with expectoration and intermittent fever for the past month. Chest X-ray shows a large (4.5 cm) left upper-lobe cavity.
Which of the following investigations leads to a definitive diagnosis?
Blood cultures
Computed tomography (CT) scanning of the chest
Mantoux test
Serum inflammatory markers
Sputum sample
Sputum sample
