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PA25.1-7 | Respiratory System — PBL Case

CLINICAL SETTING

Ramesh Kushwaha, a 54-year-old powerloom weaver from a silk-weaving cooperative on the outskirts of Varanasi, is brought to the chest OPD of the district hospital by his wife. For the past eight months he has had progressive breathlessness on exertion — he can no longer climb the single flight of stairs to his workshop. Over the last three weeks he has developed a persistent, low-grade fever (37.8–38.2 °C), drenching night sweats, and a cough that has turned productive with thick yellowish sputum. He has lost 7 kg over four months. He smoked beedis for 25 years but gave up two years ago. He has never used alcohol. His workshop, housed in a cramped 100 sq ft room, also employs six other weavers and shares a wall with a stone-polishing unit that processes sandstone artefacts for the tourist trade. On examination: thin, mildly pale, afebrile at the time of visit. Respiratory rate 22/min, SpO2 90% on room air. Trachea deviated to the right. On auscultation, dullness to percussion and absent breath sounds at the right upper zone with coarse crepitations at the right mid-zone. Cervical lymphadenopathy is present on the right side — one node is 2 × 3 cm, firm, and non-tender.

Trigger 1: Initial Presentation

Chest X-ray is taken. The radiologist's report reads: 'Right upper-lobe heterogeneous opacity with a 3.5 cm cavitary lesion and surrounding satellite nodules. Right hilar lymphadenopathy. Bilateral upper-zone fibrosis. Tracheal shift to the right. Bilateral apical calcified nodules consistent with old healed disease. Left upper-zone haziness. Small rounded opacities (< 1 cm) in bilateral mid-zones with upper-zone predominance — r/o pneumoconiosis vs miliary pattern.' Sputum sent for ZN stain, culture, and cytology. Sputum ZN smear: 3+ AFB (acid-fast bacilli seen as beaded red rods on blue background). Montoux tuberculin test: 22 mm induration.

DISCUSSION POINTS

  • What pathological process underlies the cavitary lesion seen on the chest X-ray, and what cellular and molecular events lead to cavity formation in the lung? Trace the sequence from initial bacillary implantation through granuloma formation to caseation and liquefaction.
  • Ramesh has evidence of both old healed disease (calcified apical nodules) and active disease. Explain the distinction between primary tuberculosis (Ghon complex) and secondary (post-primary) tuberculosis. Why does secondary TB preferentially involve the apices?
  • The radiologist notes bilateral mid-zone nodules and raises the possibility of pneumoconiosis. Given Ramesh's occupational exposure to sandstone dust in an adjacent unit, which specific pneumoconiosis is most likely? Describe its pathological stages and explain why silicosis also increases susceptibility to tuberculosis.
  • What organism is responsible for Ramesh's active infection? Describe its key biological properties (cell wall composition, staining characteristics, growth requirements) and explain how these properties relate to its pathogenicity and the difficulty of treating it.
Click to reveal Trigger 2: Investigations & Deterioration (discuss previous trigger first!)

Trigger 2: Investigations & Deterioration

Ramesh is admitted and started on Category I DOTS (HRZE regimen). Sputum culture grows Mycobacterium tuberculosis (sensitive to all first-line drugs). HRCT thorax confirms: bilateral upper-lobe fibrocavitary disease, miliary nodules in the lower zones, and bilateral eggshell calcification of hilar lymph nodes. On day 12 of admission, he develops high fever (39.5 °C), rigors, and pleuritic right chest pain. A new area of dullness appears at the right base. Thoracocentesis yields 180 mL of thick, foul-smelling, creamy-yellow fluid with a putrid odour. pH 6.8. Gram stain shows Gram-positive cocci in clusters and Gram-negative bacilli. The attending physician notes that Ramesh's denture-wearing neighbour in the ward also has lung disease, and points out that aspiration is a recognised route for certain organisms.

DISCUSSION POINTS

  • The pleural fluid obtained has a putrid odour and mixed Gram stain. What is the diagnosis, and what pathological process produces this appearance? Trace the pathogenesis from the initial lung infection to the pleural complication, naming the organisms most likely involved and the mechanism of foul odour.
  • The eggshell calcification of hilar nodes on HRCT is a characteristic sign. Which specific pneumoconiosis produces this sign, and how does the underlying pathological lesion (silicotic nodule) explain this radiological appearance? Compare the silicotic nodule histologically with the TB granuloma.
  • Miliary tuberculosis is seen in the lower lobes. Explain the haematogenous dissemination mechanism. Under what circumstances does containment fail, and what determines whether the pattern is miliary versus progressive organ tuberculosis?
  • Ramesh's PFTs, done before admission, showed FEV1/FVC 0.68 with reduced TLC. How do you reconcile the mixed pattern? Which component (obstructive — from prior beedi smoking) and which component (restrictive — from silicosis/fibrosis) do the spirometric indices reflect, and what pathological changes underlie each?
Click to reveal Trigger 3: Diagnosis, Complications & Management (discuss previous trigger first!)

Trigger 3: Diagnosis, Complications & Management

Ramesh responds to anti-TB therapy and surgical drainage of the empyema. However, at month 4 of treatment, follow-up HRCT shows persistent fibrocavitary disease and a new 4.5 cm peripheral mass in the right lower lobe with pleural indentation and hilar lymphadenopathy. Bronchoscopic biopsy of the mass is taken. Histology: 'Moderately differentiated squamous cell carcinoma. Intercellular bridges present. Foci of keratin pearl formation. Surrounding lung shows extensive squamous metaplasia of bronchial epithelium and areas of chronic suppurative inflammation.' PET-CT shows FDG avidity in the right lower mass and in right hilar nodes. No distant metastases. Serum calcium 11.8 mg/dL.

DISCUSSION POINTS

  • Squamous cell carcinoma has arisen in Ramesh's lung. Describe its typical location (central vs peripheral), the precursor lesion pathway (squamous metaplasia → dysplasia → carcinoma in situ → invasive carcinoma), and its characteristic gross and microscopic features. How does silicosis modify the lung cancer risk over and above smoking?
  • Ramesh's serum calcium is elevated. He has no bony metastases on PET-CT. Explain the mechanism of hypercalcaemia in this context — which molecule is responsible, which tumour cell type produces it, and how does this differ mechanistically from hypercalcaemia caused by bony metastases?
  • Review the spectrum of complications that have occurred in Ramesh's case: (a) cavity formation from TB; (b) empyema from lung abscess; (c) silicosis-related fibrosis; (d) lung carcinoma. For each, identify the specific pathological mechanism and the temporal sequence linking one complication to the next. How does occupation, past smoking, and infection interact as co-carcinogens?
  • If Ramesh's squamous cell carcinoma were instead a small-cell lung carcinoma (SCLC) presenting centrally, how would the pathology, clinical behaviour, and paraneoplastic syndrome profile differ? Describe the cell of origin, microscopic appearance, and the specific paraneoplastic syndromes unique to SCLC that you would screen for.

Group Task Assignments

Group 1: Tuberculosis — Pathogenesis and Morphology

  • Construct a detailed flow diagram of TB pathogenesis from inhalation of droplet nuclei through primary complex formation, latency, and reactivation to secondary fibrocavitary disease. Include the roles of macrophages, T-lymphocytes, TNF-α, and Type IV hypersensitivity at each step.
  • Prepare a comparison table of primary vs secondary TB: age group affected, immune status, location of lesion, fate of Ghon focus, complications, and likelihood of haematogenous spread.

Competencies: PA25.4

Group 2: Pneumonia and Lung Abscess

  • Prepare a structured table comparing lobar pneumonia and bronchopneumonia across: anatomical distribution, causative organisms, the four histological stages (lobar only), X-ray appearance, and typical patient populations.
  • Trace the pathogenesis of a lung abscess following aspiration in an alcoholic patient: which organisms are involved, why the right lower lobe posterior segment is affected, and how gross and microscopic pathology evolve over 4 weeks.

Competencies: PA25.1, PA25.2

Group 3: Obstructive Airway Disease and Spirometry

  • Using labeled spirometric loops, explain how FEV1/FVC, TLC, and DLCO differ in emphysema, chronic bronchitis, asthma, and bronchiectasis. Indicate which obstructive disease is most likely to show the 'pink puffer' vs 'blue bloater' phenotype and the underlying pathological basis.
  • Describe the pathological cycle that leads to bronchiectasis (obstruction → infection → wall destruction → dilation) and map it to its gross and microscopic features. List three Indian clinical contexts in which bronchiectasis is commonly encountered.

Competencies: PA25.3

Group 4: Occupational Lung Disease and Lung Tumours

  • Construct a comparison table for the three major pneumoconioses (coal worker's pneumoconiosis, silicosis, asbestosis): causative dust, high-risk occupations in India, lobe predilection, key histological lesion, characteristic X-ray finding, and associated malignancy.
  • Classify the main histological types of lung carcinoma (SCLC, squamous cell, adenocarcinoma, large cell). For each: state the cell of origin, location (central/peripheral), key microscopic features, molecular marker or IHC stain, and the most diagnostically important paraneoplastic syndrome.

Competencies: PA25.5, PA25.6, PA25.7

Group 5: Specimen Interpretation and Gross-Micro Correlation

  • Describe the systematic four-step framework for reading a lung specimen (gross architecture → compartment → pattern → diagnosis). Apply this framework to identify five distinct pathological diagnoses from a set of unlabelled gross and microscopic lung images.
  • Compare the gross and microscopic appearances of mesothelioma (pleural rind) vs metastatic adenocarcinoma in the pleural space. State three IHC markers that are positive in mesothelioma and negative in adenocarcinoma, and explain the clinical importance of this distinction.

Competencies: PA25.6, PA25.7

Learning Issues

Research these questions and bring your findings to the discussion.

  1. [PA25.1] What is the definition and anatomical classification of pneumonia? Describe the pathogenesis, the four sequential stages of lobar pneumonia with their gross and microscopic features, and the major complications including lung abscess formation.
  2. [PA25.2] Define lung abscess. What are its four principal aetiological mechanisms? Describe the gross and microscopic pathological features of a pyogenic lung abscess and list its major complications including empyema and secondary amyloidosis.
  3. [PA25.3] Define obstructive airway disease. Compare emphysema, chronic bronchitis, asthma, and bronchiectasis in terms of pathogenesis, histological features, spirometric changes, and complications. Distinguish the 'pink puffer' from the 'blue bloater' phenotype.
  4. [PA25.4] Describe the pathogenesis of pulmonary tuberculosis with emphasis on the role of Type IV hypersensitivity. Distinguish primary from secondary (reactivation) tuberculosis by location, morphology, and complications. Describe the Ghon complex and explain miliary TB.
  5. [PA25.5] Define pneumoconiosis. Describe the pathological stages of silicosis, its characteristic histological lesion (silicotic nodule), and explain the eggshell calcification sign. What is the epidemiological and pathological basis for the silicotuberculosis association?
  6. [PA25.6] Classify lung carcinomas into SCLC and NSCLC. Describe the pathological features, IHC profile, and paraneoplastic syndromes of squamous cell carcinoma, adenocarcinoma, and small-cell carcinoma. Describe malignant mesothelioma — its aetiology, morphology, and IHC distinction from adenocarcinoma.
  7. [PA25.7] Using a systematic specimen-reading framework, identify the gross and microscopic features that distinguish lobar pneumonia, TB granuloma, emphysema, silicosis, squamous cell carcinoma, and mesothelioma from one another in pathology specimens.