Pathology of Pneumonia PDF

Pathology of Pneumonia DR MARIE KOKOLSKI Learning Objectives • Describe the pathological features of acute pneumonia • Describe the causative agents, routes of infection and classifications of acute pneumonia • Describe the clinical symptoms, treatment and possible outcomes of acute pneumonia • De...

Pathology of Pneumonia DR MARIE KOKOLSKI Learning Objectives • Describe the pathological features of acute pneumonia • Describe the causative agents, routes of infection and classifications of acute pneumonia • Describe the clinical symptoms, treatment and possible outcomes of acute pneumonia • Describe the causative agents of chronic pneumonia Pneumonia v First described by Hippocrates (460-370 BC) v Around 220,000 people receive a diagnosis of pneumonia each year v 6th biggest cause of death in the UK and 3rd biggest case of death from lung disease v Accounts for more hospital admissions and ‘bed days’ than any other lung disease Annual number of deaths Coverage of pneumococcal vaccine Learning Objectives • Describe the pathological features of acute pneumonia • Describe the causative agents, routes of infection and classifications of acute pneumonia • Describe the clinical symptoms, treatment and possible outcomes of acute pneumonia • Describe the causative agents of chronic pneumonia Acute pneumonia Inflammatory reaction of the alveoli and interstitium of the lung usually caused by an infectious agent Characterised by ◦ Inflammatory exudate in the alveolar space that consolidates ◦ Inflammation of alveolar septa Leading cause of death from an infectious disease. Fifth most common cause of death in the US Histology NORMAL Pneumonia: Neutrophils and fluid in alveoli, congested capillaries (Red Hepatization) Organisation: exudates transformed to masses: macrophages and fibroblasts. Learning Objectives • Describe the pathological features of acute pneumonia • Describe the causative agents, routes of infection and classifications of acute pneumonia • Describe the clinical symptoms, treatment and possible outcomes of acute pneumonia • Describe the causative agents of chronic pneumonia Causative organism •Bacteria – Gram +ve: S pneumoniae, Staphylococcus aureus – Gram –ve: Haemophilus influenzae , Klebsiella pneumoniae, Legionella pneumophila • Viruses • Mycoplasma: Mycobacterium tuberculosis • Fungi: Pneumocystis jiroveci • Inorganic agents (inhaled dusts or gases) Routes of infection Aspiration of oropharyngeal secretions/gastric contents (25-35%) Inhalation of pathogens Contamination from systemic circulation Alcohol: impairs cough reflex, increased aspiration Cigarette smoke: reduced mucociliary and macrophage action Classification of pneumonia Anatomical classification – how has the infection spread in the lungs? Clinical setting in which disease occurs – what are the circumstances surrounding the disease? Microbiological – Identifying the causative agent The most clinically relevant classification is based around the circumstances surrounding the development of pneumonia Anatomical ◦ Lobar pneumonia: alveoli-alveoli ◦ Organisms access alveoli and rapidly spread via alveolar pores (connect adjacent alveoli) ◦ Adult - poor hygiene/malnourished/alcoholic ◦ Bronchopneumonia: Bronchi to alveoli ◦ Organisms colonise bronchi and spread to alveoli ◦ Affected areas consolidated locally –lobules and eventually whole lobes-confluent ◦ Young/elderly/immobile Distinction blurred -similarities in confluent bronchopneumonia Gross anatomy Clinical setting • Community acquired • Hospital acquired: Nosocomial • Immuno-compromised patient • Aspiration pneumonia • Necrotising pneumonia and lung abscess • Chronic pneumonia These sub-divisions are useful as each type of pneumonia is associated with a particular group of likely pathogens Community acquired pneumonia (CAP) • Streptococcus pneumoniae – most common cause • Haemophilus influenzae • Moraxella catarrhalis • Klebsiella pneumoniae • Pseudomonas aeruginosa • Legionella pneumophila • Viruses: influenza, metapneumovirus, COVID-19 Bacterial pneumonias are characterized by predominantly intra-alveolar neutrophilic inflammation, while viral pneumonia shows interstitial lymphocytic inflammation Hospital acquired: nosocomial • Pulmonary infection acquired in the course of a hospital stay • Underlying disease, immunosuppression, prolonged antibiotic therapy, invasive access device, mechanical ventilator • Serious, and often life threatening • Important cause of death or prolonged hospital stay • Staphylococcus aureus (gram positive cocci) • Enterobacteriacae & Pseudomonas species (gram negative rods) • Patients often have abnormal colonisation of upper respiratory tract with gram negative bacteria which colonise lower tract if immune resistance lowered Immuno-compromised Organ transplant patients/ cancer treatment/ existing disease Opportunistic infection (organisms that rarely cause disease in normal host) ◦ Bacteria: Mycobacterial infection ◦ Viruses: Cytomegalovirus (CMV), Herpes simplex ◦ Fungi: Pneumocystis jiroveci, Candida, Aspergillus + usual bacterial/viral/fungal organisms Aspiration pneumonia § Aspiration of gastric contents: ◦ ◦ ◦ ◦ Abnormal gag/swallow reflexes e.g. after a stroke, MS Unconsciousness Repeated vomiting Poor oral hygiene § Pneumonia is due to both irritation of gastric contents and bacteria § Anaerobic bacteria: oral flora § Aerobic: ◦ S pneumoniae, S aureus, H influenza, Pseudomonas aeruginosa § Often necrotising, frequent cause of death, abscess formation in survivors Necrotising pneumonia and lung abscess • Complication/progression of pneumonia • Inflammation and damage results in reduction of vascular supply to tissue – cell death • Access for antibiotics reduced – infection progresses • Frequently causes death • Survivors often have lung abscesses • Aspiration of infected material – most common cause • Can resolve with antimicrobial therapy leaving a scar Learning Objectives • Describe the pathological features of acute pneumonia • Describe the causative agents, routes of infection and classifications of acute pneumonia • Describe the clinical symptoms, treatment and possible outcomes of acute pneumonia • Describe the causative agents of chronic pneumonia Symptoms and treatment of acute bacterial pneumonia Symptoms: ◦ ◦ ◦ ◦ Fever, chills, dyspnoea Cough with or without sputum (purulent – bacterial, watery – viral) Crackles on auscultation Consolidation in radiograph Diagnosis: ◦ Sputum: Bacteria/virus. Gram staining, bacterial culture (suitable antibiotic) ◦ X-ray ◦ FBC Treatment: Antibiotic (empirically-can be changed on results) Possible outcomes of pneumonia • Resolution: destruction of connective tissue/vasculature minimal/absent. Neutrophils destroy organism, exudate liquified by neutrophil enzymes (fibrin breakdown /phagocytosis of dead cells), this is coughed up/reabsorbed by capillaries/drained in lymph. Epithelial stem cell proliferation and differentiation into type I and II pneumocytes • Organisation: scar tissue/fibrosis from destruction of connective tissue. Possible bronchiectasis. • Abscess formation • Empyema • Bacteremia (meningitis/arthritis/infective endocarditis) • Death Learning Objectives • Describe the pathological features of acute pneumonia • Describe the causative agents, routes of infection and classifications of acute pneumonia • Describe the clinical symptoms, treatment and possible outcomes of acute pneumonia • Describe the causative agents of chronic pneumonia Chronic pneumonia • Often a localised lesion in an immunocompromised patient • Typically a granulomatous inflammation • Caused by bacteria (e.g. Mycobacterium tuberculosis) or fungi § Histoplasma capsulatum – infection can occur in immunocompetent individuals § Blastomyces dermatitidis – soil-inhabiting fungus § Coccidiodies immitis – pyogenic, granulomatous or mixed