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Infectious Diseases > Tuberculosis > Flashcards

Tuberculosis Flashcards

1
Q

What organisms cause tuberculosis?

A

There are 4 (the Mycobacterium tuberculosis complex):

  • M. tuberculosis
  • M. bovis
  • M. africanum
  • M. microti
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2
Q

What sort of bacteria are the tuberculosis causative organisms?

A

Obligate aerobes

Facultative intracellular pathogens

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3
Q

What sort of cells does tuberculosis generally infect?

A

Mononuclear phagocytes

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4
Q

How is tuberculosis spread?

A

Airborne disease spread by respiratory droplets.

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5
Q

What is primary tuberculosis?

A

First infection with MTb.

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6
Q

Outline the pathogenesis of primary Tb.

A
  1. Inhaled into lung
  2. Alveolar marophages ingest bacteria
  3. Bacilli proliferate inside M0 trigger release of Neutrophil chemoattractants; inflamm infiltrate in lung and hilar LN
  4. M0 present antigen to T cells
  5. Delayed type hypersensitivity –> tissue necrosis and granuloma formation.
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7
Q

Describe the structure of a granuloma.

A

Central area of necrotic material (caseation), surrounded by epithelioid cells and Langhan’s giant cells with multiple nuclei.
Lymphocytes present
Varying degree of fibrosis

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8
Q

What happens after a granuloma heals?

A

Granuloma becomes calcified.
Some calcified nodules contain bacteria - these are contained by the immune system (and the hypoxic, acidic environment of the granuloma). May be dormant for many years.

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9
Q

How does the Ghon focus appear on CXR?

A

Small calcified nodule often within the upper parts of the lower lobes or the lower parts of the upper lobes, seen in the midzone.

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10
Q

What is the primary complex of Ranke?

A

A focus within the regional draining lymph node.

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11
Q

What is latent Tb?

A

Most infected people develop cell-mediated immunity to bacteria = latent infection.

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12
Q

What are the clinical features of pulmonary TB?

A
  • Productive cough
  • +/- haemoptysis
  • Systemic: LOW, fever, sweats (EOD and night)
  • If involving larynx: hoarse voice and cough
  • If involving pleura: pleuritic chest pain
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13
Q

What are the clinical features of lymph node TB?

A

Extrathoracic nodes more common (than intrath or mediastinal).
Firm, non-tender enlargement of a cervical or supraclavicular node.
Node becomes necrotic centrally > can liquefy > becomes fluctuant.

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14
Q

What are the clinical features of miliary TB?

A

Haematogenous spread to multiple sites inc CNS (20%).

  • Systemic upset, resp symptoms
  • +/- liver and splenic microabscesses
  • Deranged LFTs, or cholestasis and GI symptoms
  • CXR shows miliary seed like presentation
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15
Q

What are the appropriate diagnostic investigations in pulonary, pleural and laryngeal TB?

A

Smear and culture of:

  • Sputum (>2 samples increases diagnostic yield)
  • Bronchoalveolar lavage fluid if cough unproductive
  • Aspiration of pleural fluid and pleural biopsy
  • Gastric aspirates (paediatric disease)
  • Nasoendoscopic or bronchoscopic exam/biopsy/smear of vocal cords in laryngeal disease.
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16
Q

What are the Dx Ix in miliary TB?

A
  • blood cultures
  • bronchoalveolar lavage fluid (usually smear negative, culture positive)
  • LP in all cases to assess CNS involvement
17
Q

What are the characteristics of LP fluid in CNS TB?

A

CSF protein may be very high (>2-3g/L)

CSF glucose

18
Q

What are the Ix in LN TB?

A

Histocytopathological examination, culture and smear of:

  • FNA or biopsy of LN under radiological guidance
  • Mediastinal nodal sampling (EBUS, mediastinostomy)
19
Q

What is the duration of treatment for TB?

A

6 months, excluding CNS TB which requires 12 months.

20
Q

In which forms of TB are corticosteroids used?

A

Corticosteroids used in CNS and pericardial TB to reduce long term complications.

21
Q

AEx rifampicin?

A
  • Induces liver enzymes
  • Liver enzyme induction –> reduces efficacy other Rx
  • Thrombocytopaenia reported
  • Stains body secretions pink
  • OCP ineffective
22
Q

AEx isoniazid?

A

Very few

  • High doses > polyneuropathy due to B6 deficiency (interferes with pyridoxal phosphate)
  • Occasionally rash
23
Q

AEx pyrazinamide?

A
  • May cause hepatic toxicity (rare).

- Reduces renal excretion of urate > may precipitate gout

24
Q

AEx ethambutol?

A

Dose related optic retrobulbar neuritis: presents with green colour blindness, reduction in visual acuity and central scotoma

25
Q

AEx streptomycin?

A

Irreversible damage to vestibular nerve: more likely in elderly and those with renal impairment.
Allergic rxn more common than with other drugs

26
Q

When is streptomycin used?

A

Used only if patients very ill, have MDR TB or not responding adequately to Rx.

Infectious Diseases (10 decks)

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