Tuberculosis (TB) Flashcards
What is TB and what organism is it caused by ?
It is an infection caused by Mycobacterium tuberculosis that most commonly affects the lungs
What is the shape and gram stain of Mycobacterium tuberculosis?
Rod shaped gram positive bacillus
How is TB spread?
Via aerosol route (coughing, sneezing)
List the people most commonly affected by TB infection
- Ethnic minority groups (predominantly from South Asia and sub-Saharan Africa)
- Homeless patients, those with alcohol dependency and other drug misusers
- Malnutrition
- HIV-positive and other immunocompromised patients e.g. caused by immunosuppressive drugs
- Elderly patients: latent tuberculosis infection (LTBI) may reactivate in elderly patients.
- Children: young children are particularly susceptible to mycobacterial infection, due to their immature immune systems.
Describe the pathogenesis of a primary TB infection
- A non-immune host is exposed to M. tuberculosis (primary infection)
- Host macrophages in the lung engulf the organisms and carry them to hilar lymph nodes in an attempt to control infection. The lung lesion plus affected lymph nodes is referred to as a Ghon complex.
- Some organisms may disseminate via the lymphatics or bloodstream to distant sites. Small granulomas (with caseous necrosis in the centre) are formed around the body to contain the mycobacteria.
- These may heal spontaneously by fibrosis and the bacteria are eliminated (in 80% of cases) or bacteria are encapsulated in a defensive barrier but persist in an otherwise healthy individual where the disease is considered dormant (latent).
- Only a small proportion of patients progress to overt (active) TB.
Describe the difference between active and latent TB infection
- Persons with latent TB infection do not feel sick and do not have any symptoms. They are infected with M. tuberculosis, but do not have TB disease. The only sign of TB infection is a positive reaction to the tuberculin skin test or TB blood test.
- Active TB is where TB bacteria overcome the defenses of the immune system and begin to multiply, resulting in the progression from latent TB infection to TB disease. Some people develop TB disease soon after infection, while others develop TB disease later when their immune system becomes weak.
Is someone with latent TB infectious ?
- No - Persons with latent TB infection are not infectious and cannot spread TB infection to others.
- Only active TB is infectious
Define what is meant by millary TB ?
This is when when the primary infection is not adequately contained and invades the bloodstream, resulting in severe disease.
Describe what is meant by secondary TB infection and state where it most commonly occurs in the body and give examples of the causes for it
This is where someone with latent TB, has there TB reactived (to active TB), this is usually due to the host becoming immunocompromised.
Reactivation generally occurs in the apex of the lungs and may spread locally or to more distant sites. Possible causes of immunocomprise include:
- immunosuppressive drugs e.g. steroids
- HIV
- malnutrition
Does TB only affect the lungs ?
No - The bacteria usually attack the lungs, but TB bacteria can attack any part of the body such as the kidney, spine, and brain.
- The lungs remain the most common site for secondary TB.
- However extra-pulmonary infection may occur, list the areas which it may occur outside the lungs
- CNS (tuberculous meningitis - the most serious complication)
- Vertebral bodies (Pott’s disease)
- Cervical lymph nodes (scrofuloderma)
- Renal
- Gastrointestinal tract
What are the general symptoms of TB ?
- Fatigue
- Malaise
- Fever
- Night sweats
- Weight loss & loss of appetite (anorexia)
- Failure to thrive
What are the additional features alongisde the general symptoms of TB suggestive of pulmonary TB ?
- Cough + sputum
- Haemoptysis (can be massive)
- Pleurisy
- Pleural effusion
What are the additional features alongisde the general symptoms of TB suggestive of Miliary TB ?
Severe disease with poor immune response can produce a picture like millet seeds over the CXR.
What are the additional features alongisde the general symptoms of TB suggestive of genitourinary TB ?
- Often presents with sterile pyuria (pus in urine)
- Dysuria
- Polyuria
- Haematuria
- Loin/back pain
What are the additional features alongisde the general symptoms of TB suggestive of spinal TB (potts disease) ?
- Severe back pain
- Arthritis
- Osteomyelitis and abscess formation (eg, loin mass or psoas abscess from spinal TB)
- Nerve root compression
- Isolated bone or joint lesions (monoarthritis).
What are the additional features alongisde the general symptoms of TB suggestive of skin TB ?
Erythema nodosum (represents an early immunological response to infection), skin sinus formation (‘scrofuloderma’), erythema induratum
What are the additional features alongisde the general symptoms of TB suggestive of GI TB ?
- Abdominal pain
- Bloating
- Obstruction
- Simulating appendicitis
- Occasionally ascites
What are the additional features alongisde the general symptoms of TB suggestive of pericardial TB ?
Initially nonspecific; may be signs of pericardial effusion (pulsus paradoxus, elevated JVP) or constrictive pericarditis.
What are the additional features alongisde the general symptoms of TB suggestive of TB meningitis ?
- Prodrome - Fever, headache, vomiting, abdo pain, drowsiness, meningism & delirium. Often worsens over 1-3weeks
- CNS signs - seizures, tremor, papilloedema, CNS palsies
What is the treatment of CNS TB ?
Isoniazid (with pyridoxine), rifampicin, pyrazinamide and ethambutol (RIPE) for 2 months then isoniazid (with pyridoxine) and rifampicin for a further 10 months.
Who do you screen for TB in/ screen for latent TB?
Those who have been in close contact of a person with pulmonary/laryngeal TB or have come to the country from a high TB incidence country
How is latent TB diagnosed/ how do you screen for TB?
- 1st line = mantoux test
- 2nd line = if mantoux test positive, unclear, or patient is someone the test may be fasly negative in then do interferon-gamma testing to confirm
Who may the mantoux screening test for TB be fasly negative in?
Those who have:
- Miliary TB
- Sarcoidosis
- HIV
- Lymphoma
- Are very young (<6months)
