TUBERCULOSIS Flashcards
What is the organism that most commonly causes tuberculosis (TB)?
Mycoplasma tuberculosis is a aerobic bacteria with an unusual waxy coating on its cell surface. This renders it impervious to Gram staining, although it is considered Gram positive.
Where in the lungs does the bacterium usually implant itself and why?
In the upper lobes because this is where the oxygen partial pressure is the highest.
Do most patients with TB display symptoms?
No. Most cases of TB are latent. The infection is controlled by the cell mediated immune system. Tissue will heal through scar formation and eventual calcification, which may be seen on a chest x-ray.
Which group of patients is most often affected by primary pulmonary TB?
Immunocompromised patients. It is the leading cause of death in patients with HIV.
What is the UK incidence of TB?
8,200 per year. It results in 350 deaths per year in the UK.
Explain briefly how M. tuberculosis causes disease.
The organism finds its way into an alveolar macrophage through phagocytosis. M. tuberculosis then replicates within the cell. Granulomas are then formed as other macrophages, T and B lymphocytes and fibroblasts aggregate around the infected macrophage. The bacteria can remain dormant in the granuloma or can spread to other parts of the body via the lymphatic system and then the blood stream. Tubercles form around the granuloma and necrosis will happen at the centre of the tubercle.
How is the necrosis that occurs in tuberculosis described, describing its texture and appearance?
Caseous necrosis named because it seems to have the texture of soft white cheese.
What is the primary site of infection in the lung known as?
The Ghon focus
Where might M. tuberculosis spread to?
Almost anywhere. Peripheral lymph nodes, the kidneys, the brain and bones. It rarely affects the heart, skeletal muscle, the pancreas or the thyroid.
What is a Ghon complex?
When tubercle bacilli drain into the local lymph nodes, the lesion in the lung plus the granulomas in the lymph node all form the ghon complex.
How are M. tuberculosis organisms identified in histology?
Ziehl-Neelsen staining. This picks up acid fast bacteria.
What is secondary pulmonary tuberculosis?
The form of disease that arises in a previously sensitised host. Usually arises from reactivation of dormant primary lesions.
What is cavitating tuberculosis?
This is when the apical lesion enlarges significantly through necrosis. There is an expansion of the area of caseation creating a ragged edge to the lung.
There is erosion of the vessels which leads to haemoptysis. This means that likelihood of infection spreading is very high.
Patient is coughing up necrotic tissue so infection can spread to upper airway or other lung.
What is miliary tuberculosis?
Form of tuberculosis characterised by wide dissemination into the body and by the tiny size of the lesions (1-5 mm). These foci of consolidation may expand and coalesce. The organism drains into the lymphatics and then into the blood stream. It can affect any number of organs, including the lung, liver, spleen, bone marrow, meninges, fallopian tubes and epididymis.
What is open tuberculosis?
This is the rapid spread of the organism through the airways. It is also called Tuberculous Bronchopneumonia. There is extensive parenchymal inflammation.
