Tuberculosis Flashcards
Causative organism of TB.
Mycobacterium tuberculosis
Where is most of TB cases seen?
Africa and Asia
Risk factors of developing TB.
Origination from a high-incidence country
Frequent travel to high-incidence areas
Immunodeficiency
Drug/alcohol misuse
Homelessness/Hostels/Overcrowding
Characteristics of Mycobacterium tuberculosis.
Aerobic intracellular pathogen.
Relatively impermeable to acid-based dyes leaves it called acid-fast bacilli + red staining on Zeihl-Neelsen staining.
It is an airborne infection spread by coughing via respiratory droplets.
Explain pathogenesis of primary TB.
Bacteria reaches alveolar macrophages. The macrophages ingest the bacteria and subsequent inflammatory reaction leads to tissue necrosis and formation of a granuloma.
It is a caseating granuoma surrounded by epithelioid cells and Langhans giant cells.
The caseated area heals, some heal completely, some become calcified.
Some calcified nodules will contain the bacteria. The immune system will prevent it from getting out and it can lay dormant for years.
They lay dormant in the primary/Ghon’s focus.
This can be seen on a CXR.
What is the most common cause of active TB?
Reactivation of latent TB.
It is usually not the immediately from the primary infection.
When might newly acquired TB occur?
In HIV patients.
Risk factors for reactivation of latent TB.
HIV co-infection
Immunosuppressant therapy
DM
End stage CKD
Ageing
Clinical features of TB in general.
Cough
Haemoptysis
Fever
Night sweats
Weight loss
Lymphadenopathy
Erythema nodosum
Spinal pain
When suspecting TB, which investigations should be done?
Sputum sample (3x)
Gram stain
Biopsy samples
Fluid for microscopy
Smear
Culture
CXR
Symptoms of pulmonary TB.
Productive cough
Haemoptysis
Hoarse voice and severe cough if there is laryngeal involvement.
Pleuritic pain if the pleura has been affected.
Findings on CXR of TB.
Consolidation with or without cavitation.
Pleural effusion
Thickening or widening of mediastinum by hilar or paratracheal adenopathy.
Primary TB may show patchy consolidation, pleural effusions and hilar lymphadenopathy
Reactivated TB may show patchy or nodular consolidation with cavitation (gas filled spaces in the lungs) typically in the upper zones
Disseminated Miliary TB give a picture of “millet seeds” uniformly distributed throughout the lung fields
How should sputum samples be collected in TB?
Serial sputum sample on at least 3 occassions.
This should be done first thing in the morning.
What does a smear-positive sputum tell you about the TB?
The patient is considered to be infectious and should be isolated.
What does a smear-negative and a culture-positive result tell you about the patient?
Less infectious and generally do not need to be isolated.
What is the second most commonly affected organ in TB?
Lymph nodes.
What lymph nodes are involved?
Extrathoracic more commonly than intrathoracic and mediastinal.
It is usually firm, non-tender enlargement of the cervical or supraclavicular lymph nodes.
Clinical features of lymph node TB.
Node is necrotic centrally and can liquefy.
Overlying sin is frequently hard and firm (indurated).
There can be sinus tract formation with purulent discharge.
Usually no erythema.
This is called a cold abscess formation.
When are nodes enlarged compared to diagnosis of TB?
Can be enlarged for several months prior to the diagnosis.
Investigations of lymph node TB.
Fine needle aspiration via ultrasound guidance.
Core biopsy
If necessary removal of the lymph node.
Samples should be sent for AFB smear, culture and cytology to exclude cancer.
What other systems might TB affect?
GI tract
Bone and spine
General (miliary)
CNS
Pericardium
Skin
What might TB affect in the GI tract?
Intestines and peritoneum
Clinical features of GI TB.
Abdo pain
Weight loss
Anaemia
Fever with night sweats
Obstruction
Right iliac fossa pain or palpable mass
Usually it is the ileocaecal area that is affected.
Diagnosis of GI TB.
Small bowel follow-through
USS, MRI or CT
Histology and culture of tissue
