Pathology of Respiratory Tract Infection Flashcards
What is pneumonia and what occurs?
Disease of the lungs - infection involving distal airspaces, usually with inflammatory exudation (“localised oedema”)
Fluid-filled spaces lead to CONSOLIDATION
Different methods of pneumonia classification?
By clinical setting, e.g: CAP and HAP
By organism, e.g: Mycoplasma, Pneumococcal, etc
By morphology - by parts of the lungs invovled; e.g: lobar pneumonia, bronchopneumonia)
Different organisms that can cause pneumonia?
Viruses - common and often self-limiting but can be complicated, e.g: influenza, parainfluenza, measles, varicella-zoster (often in children), Respiratory Syncitial Virus (RSV)
Bacteria - Chlamydia, Mycoplasma, Fungi
What is and what causes lobar pneumonia?
CONFLUENT CONSOLIDATION involving a COMPLETE LUNG LOBE (alveoli will have fluid in them)
Most often due to Streptococcus pneumoniae (pneumococcus) but also with other, e.g: Klebsiella, Legionella
Describe the pathology of pneumonia
Acute inflammatory response:
Exudation of fibrin-rich fluid
Neutrophil infiltration
Macrophage infiltration (clear debris)
Resolution
In early phase, no antibodies produced but later on they are; antibodies cause OPSONISATION (stick to bacteria and then them susceptible to phagocytosis)
Complications of pneumonia?
ORGANISATION (fibrous scarring):
Inflammatory exudate not fully removed
Granulation tissue forms, then scar tissue which can lead to BRONCHIECTASIS
ABSCESS can lead to EMPYEMA (pus in pleural space)
What is bronchopneumonia and who gets it?
Infection starting in airways and spreading to adjacent alveolar lung
Who gets bronchopneumonia?
Most often seen in context of pre-existing disease and can start with bronchitis, e.g: person may have COPD, CHD/heart failure (elderly), complication of a viral infection (influenza), ASPIRATION of gastric contents (alcoholic)
Organisms causing bronchopneumonia?
More varied: Strep. pneumoniae Hameophilus influenzae Staphylococcus Anaerobes Coliforms
Staph, anaerobes and coliforms are seen in aspiration, so often treated with > 1 antibiotic
Describe a lung abscess, what it is, symptoms and context
Localised collection of pus that is tumour-like/presents as a mass lesion in lungs
Can cause chronic malaise and fever
Context: is seen in aspiration
What is and what causes bronchiestasis? Problems?
Abnormal FIXED DILATATION of bronchi (dilated airways accumulate purulent secretions; if pathogens are inhaled into this, can causes recurrent infections) Usually due to fibrous scarring following infection, like pneumonia, TB, CF - physiotherapist tries to prevent bronchiectasis in CF )
Also seen with chronic obstruction, like a tumour, as there is scarring behind
Describe tuberculosis
Mycobacterial infection that is a chronic infection describe in many body sites, e.g: lungs, gut, kidneys, lymph nodes, skin
Pathological characteristic of TB?
Delayed (type IV) HYPERSENSITIVITY (granulomas - accumulation of macrophages and giant cells - with necrosis) - immune system causes most of the damage in TB, due to T cell stimulation
Main organisms causing TB?
In humans:
- M. tuberculosis*
- M. bovine*
Pathology of TB caused by other organisms?
Others - cause atypical infection, esp. in immunocompromised host
Pathogenicity is due to ability:
To avoid phagocytosis
To stimulate a host T-cell response, instead of an acute inflammatory response (causing granuloma formation and necrosis)
Explain immunity and hypersensitivity in TB?
Commonly, both processes occur together:
T-cell response to organism ENHANCES MACROPHAGE ABILITY to KILL mycobacteria - ability constitutes IMMUNITY
T-cell response causes GRANULOMATOUS INFLAMMATION, tissue NECROSIS and SCARRING - this is HYPERSENSITIVITY (type IV)
Balance of the two will decide the no. of organisms found
Describe primary TB
1st exposure and up to 5 yrs after (when there is no immunity/BCG):
Inhaled organism phagocytosed and carries to HILAR LYMPH NODES (enlarge). Immune activation takes a few weeks and leads to granulomatous response in nodes + lung, usually killing organism
Sometimes, infection is overwhelming and spreads (if genetically, T cells are not effective enough or individual is malnourished)
Describe secondary TB
Reinfection/reactivation of disease in a person with SOME immunity
Disease tends to initially remain localised, leading to apical lesions (assman focus) but can progress to spreading via airways and/or bloodstream
Tissue changes in primary TB?
Gohn focus (small) is an area of infection and caseous necroses in the PERIPHERY of the MID ZONE of the lung, beneath the pleura; this is found in TB
Large hilar nodes (granulomatous)
May see caseous necrosis
Method of narrowing down to TB?
Acid/alcohol fast bacilli stain
Tissue changes in secondary TB?
Fibrosing and CAVITATING apical lesion (cancer is an important differential diagnosis)
What is miliary TB?
Widespread dissemination of the organism (white foci will be seen spread out)
What is galloping consumption?
TB bronchopneumonia speed of progression
Why does TB reactivate?
Due to decreased T-cell function with:
Age
Coincident disease (HIV) I
mmunocompromisation (cancer)
Immunosuppressive therapy (steroids, chemotherapy)
OR
Due to reinfection at high dose/with more virulent organism
Describe infection in the immunocompromised host and give examples
Virulent infection with common organism, e.g: TB
Infection with OPPORTUNISTIC pathogen, e.g: Virus - cytomegalovirus (CMV)
Bacteria - Mycobacterium avium intracellulare is common in HIV Fungi - aspergillus, canidida, pneumocystic (PCP) Protozoa - cryptosporidia, toxoplasma
How to make an infection diagnosis?
High index of suspicion
Teamwork
Broncho-alveolar lavage (BAL) - bronchoscope is passed through the mouth/nose into the lungs and fluid is squirted into a small part of the lung and then collected for examination
Biopsy (with many stains)
Problems with cavities?
May be from previous TB; can fill with, e.g; aspergillus and cause problems like fatal haemorrhage
Antibiotics may not be able to get into the cavity
Differences between lobar pneumonia and bronchopneumonia
Lobar pneumonia - affects the lobe of a lung (complete consolidation); in 90% of cases, the cause is Strep. pneumoniae, with other potential causes being Staph. aureus and Klebsiella
Bronchopneumonia - affects the airways and then the alveoli; the organisms causing this are more varied, like H. influenzae, Strep anaerobes and Coliforms
