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PA3.1-4,PA4.1 | Inflammation & Healing — PBL Case

CLINICAL SETTING

Meenakshi, a 19-year-old nursing student from a small town in Tamil Nadu, is admitted to the medicine ward of a tertiary care hospital with a 6-week history of fever (evening spikes up to 39.2 °C), night sweats, 6 kg weight loss, and a dry, persistent cough. Over the past 10 days she has developed worsening right-sided pleuritic chest pain and progressive breathlessness. On examination her trachea is deviated to the left, percussion is stony dull over the right lower chest, and breath sounds are absent below the right mid-zone. Her pulse is 110/min and temperature 38.8 °C. CXR shows a large right-sided opacity with a concave upper border obliterating the costophrenic angle. Mantoux test: 22 mm induration. Diagnostic aspiration yields 80 mL of thick, creamy, foul-smelling yellow fluid that clots on standing. The intern asks: what is happening inside Meenakshi's pleural cavity, and why did her body not simply 'switch off' the inflammation weeks ago?

Trigger 1: The Fluid in the Chest

Pleural fluid is sent to the laboratory. Results: protein 52 g/L (serum protein 68 g/L), LDH 820 U/L (serum LDH 190 U/L), pH 6.8, glucose 1.1 mmol/L, specific gravity 1.026. Microscopy shows 98,000 WBC/µL — predominantly neutrophils — with abundant cellular debris, fibrin strands, and gram-positive cocci in clusters. The microbiologist flags the sample: secondary staphylococcal empyema. The resident explains to the intern: the pleural space is now showing a specific morphological pattern of acute inflammation. The radiology registrar adds: the upper concave border on CXR represents fluid, but the lower zone shows a loculated pocket that looks almost solid — and the pathologist will tell us why after thoracocentesis.

DISCUSSION POINTS

The pleural fluid has protein 52 g/L, LDH 820 U/L, and pH 6.8. Classify this fluid as transudate or exudate using Light's criteria and explain the vascular mechanism that produces each component of an exudate during acute inflammation.
The fluid contains 98,000 neutrophils/µL. Describe the step-by-step leucocyte recruitment cascade — margination, rolling, firm adhesion, transmigration — naming the specific molecular adhesion molecules involved at each step.
Once in the pleural space, neutrophils attempt to kill the staphylococci. Describe the respiratory burst pathway, naming the enzymes (NADPH oxidase, myeloperoxidase), reactive oxygen species generated, and at least one non-oxidative killing mechanism.
Which chemical mediators are primarily responsible for Meenakshi's fever, pleuritic pain, and vascular permeability increase? Distinguish between cell-derived (histamine, leukotrienes, prostaglandins) and plasma-derived (complement, kinins) mediators and their specific roles.

Click to reveal Trigger 2: The Chest Tube and What It Drains (discuss previous trigger first!)

Trigger 2: The Chest Tube and What It Drains

Meenakshi has a chest drain inserted. Over 48 hours, 1.2 litres of thick pus drains. The lung fails to fully expand, and CT shows a thick, fibrous 'peel' encasing the right lung — a fibrothorax. The surgeon considers decortication. Meanwhile, Meenakshi's sputum returns a positive smear for acid-fast bacilli. Her original admission Mantoux and a sputum culture confirm Mycobacterium tuberculosis. The team now realises the pleural empyema is a secondary bacterial infection superimposed on a primary TB pleuritis. The pathologist reviews an earlier pleural biopsy taken during the diagnostic thoracocentesis and reports: 'Sections show a granuloma composed of aggregated epithelioid histiocytes with Langhans giant cells, central caseous necrosis, and a surrounding lymphocytic cuff.' The surgeon asks: what was happening at the cellular level inside the pleural tissue before the staphylococci arrived?

DISCUSSION POINTS

The pathologist describes a granuloma with epithelioid histiocytes, Langhans giant cells, central caseous necrosis, and a lymphocytic cuff. Define chronic granulomatous inflammation, explain each of these four components using their cellular origin and function, and describe how the granuloma forms step by step.
Distinguish Langhans giant cells from foreign-body giant cells — by nuclear arrangement, the condition they indicate, and their mechanism of formation. Why does the immune system form giant cells rather than simply using more neutrophils?
Meenakshi has both acute suppurative inflammation (empyema) and chronic granulomatous inflammation (TB pleuritis) occurring simultaneously. How do macrophages behave differently in acute vs chronic inflammation — in terms of M1/M2 polarisation, cytokines produced, and interaction with T-lymphocytes?
The fibrothorax represents a fibrotic outcome. Using the four outcomes of acute inflammation (resolution, fibrosis, abscess formation, chronic inflammation), explain why fibrosis rather than resolution occurred in Meenakshi's pleural space, and what molecular signals (TGF-β, IL-13, PDGF) drive pleural fibrosis.

Click to reveal Trigger 3: Healing After Decortication (discuss previous trigger first!)

Trigger 3: Healing After Decortication

Meenakshi undergoes right thoracotomy and decortication. The surgeon strips the thick fibrous peel off the visceral pleura. Post-operatively, the lung re-expands well on CXR. The wound is closed primarily with interrupted sutures. On day 3 the wound edge is tender, slightly erythematous, and shows a thin layer of fibrinous exudate. By day 10 the surgical wound is healing well; a small biopsy for academic interest shows abundant new capillaries with plump endothelial cells, proliferating fibroblasts, and loose immature collagen in an oedematous matrix. By week 6 the wound is a flat, pale, strong scar. Simultaneously, the pleural cavity, which had a large tissue defect after stripping, fills with granulation tissue that contracts and matures over 3 months. Meenakshi's nutritional status, however, is borderline — serum albumin at surgery was 2.4 g/dL and she was anaemic (Hb 9.1 g/dL). The surgical resident asks: will the wound heal normally, and what cellular and molecular events drive each phase of repair?

DISCUSSION POINTS

The day-10 biopsy shows angiogenesis, proliferating fibroblasts, and loose immature collagen — describe what tissue type this represents, name the growth factors (VEGF, PDGF, FGF, TGF-β) that drive each component, and explain how this tissue type differs from a mature scar at 6 weeks.
Meenakshi's surgical wound is healing by primary intention. Compare the cellular and molecular events of primary vs secondary intention healing, explaining why the pleural cavity (large tissue defect) must heal by secondary intention and why wound contraction by myofibroblasts is essential in secondary healing.
Meenakshi's albumin is 2.4 g/dL and Hb 9.1 g/dL at surgery. Explain the specific mechanisms by which hypoalbuminaemia, anaemia, and the catabolic state of chronic TB infection each impair wound healing — linking each deficiency to a specific phase of the repair cascade.
Three months post-surgery, the pleural cavity has fully contracted and Meenakshi's lung function is near normal. Construct a brief pathology narrative of the entire clinical journey — from the initial TB infection through acute pleuritis, secondary empyema, granuloma formation, fibrothorax, surgical repair, and final scar maturation — identifying the cell types and mediators dominant at each stage.

Group Task Assignments

Group 1: Vascular events and mediators of acute inflammation

Draw a timeline of the vascular response from the moment bacteria enter the pleural space to the formation of pus at 24 hours: include vasoconstriction, vasodilation, increased permeability, exudate formation, leucocyte margination, and emigration. Label each step with the mediator responsible.
Prepare a structured comparison table of the key chemical mediators of acute inflammation covering: histamine, serotonin, prostaglandins (PGE2), leukotrienes (LTB4, LTC4), IL-1, TNF-α, and C5a — for each state the source cell, trigger for release, and primary effect in acute inflammation.

Competencies: PA3.1, PA3.2

Group 2: Morphological patterns of acute and chronic inflammation

Using microscopy images from the practical, identify: (a) fibrinopurulent exudate on the pleural surface (serous/fibrinous pattern), (b) abscess cavity (suppurative pattern) showing central liquefaction and peripheral pyogenic membrane, (c) granuloma with epithelioid histiocytes, Langhans giant cells, and caseous necrosis. For each, describe the cells present, the tissue change, and match to the inflammatory pattern.
Create a diagnostic decision table: given a histology slide, which dominant cell type points to which inflammatory diagnosis? Include neutrophils, lymphocytes, plasma cells, macrophages, epithelioid histiocytes, and eosinophils.

Competencies: PA3.3, PA3.4

Group 3: Granuloma formation and chronic inflammation mechanisms

Map the cellular dialogue that produces a TB granuloma: Mycobacterium → macrophage engulfment → failure to kill → IL-12 release → Th1 activation → IFN-γ production → macrophage activation to epithelioid histiocyte → giant cell formation → lymphocytic cuff. Annotate each step with the cell type, cytokine, and outcome if this step fails (e.g., HIV-related defect in CD4 Th1 response → no granuloma → miliary TB).
Research and present the clinical significance of granulomatous inflammation beyond TB: choose ONE of sarcoidosis, Crohn's disease, or schistosomiasis. Describe the type of granuloma (caseating vs non-caseating), the inciting antigen, and the clinical consequence of failed granuloma resolution.

Competencies: PA3.3, PA3.4

Group 4: Repair, regeneration, and wound healing

Draw the four overlapping phases of wound repair (haemostasis, inflammation, proliferation, remodelling) on a timeline from day 0 to month 6. For each phase indicate: dominant cell type, key growth factor/cytokine, extracellular matrix change, and the clinical appearance of Meenakshi's wound at that timepoint.
Analyse the factors impairing wound healing in Meenakshi's case — hypoalbuminaemia, anaemia, chronic infection, catabolic state — and for each propose a clinical intervention to optimise healing before and after surgery.

Competencies: PA4.1

Group 5: Systemic effects and clinico-pathological synthesis

Explain Meenakshi's systemic signs — fever, night sweats, weight loss, elevated ESR and CRP — in terms of the cytokines released during chronic inflammation (IL-1, IL-6, TNF-α). Describe the acute-phase response: which proteins rise (CRP, fibrinogen, serum amyloid A) and which fall (albumin, transferrin), and how this explains both her anaemia and her hypoalbuminaemia.
Write a mock histopathology report for the pleural biopsy: specimen description, microscopic findings (granuloma components, necrosis type, inflammatory cells), differential diagnosis (TB vs sarcoidosis vs fungal), final diagnosis, and a clinical note recommending ZN stain/culture and TB PCR.

Competencies: PA3.1, PA3.3, PA4.1

Learning Issues

Research these questions and bring your findings to the discussion.

[PA3.1] What are the vascular and cellular events of acute inflammation, and how do they explain the five cardinal signs? What distinguishes exudate from transudate, and how does each form?
[PA3.2] Which chemical mediators are responsible for each feature of Meenakshi's inflammation — fever, pain, vascular permeability, neutrophil recruitment — and what is the source, trigger, and specific action of each mediator?
[PA3.3] What is chronic granulomatous inflammation? What are the components of a TB granuloma, how does it form step-by-step, and how does a Langhans giant cell differ from a foreign-body giant cell morphologically and in clinical significance?
[PA3.4] How do you identify acute vs chronic vs granulomatous inflammation on a histology slide? What cell types, nuclear features, and tissue changes characterise each pattern?
[PA4.1] What are the four phases of wound repair and what cellular/molecular events occur in each? How does primary intention healing differ from secondary intention healing, and which specific factors in Meenakshi's condition will impair each phase of her repair?