20 types respiratory system disease treatment investigation finding differential diagnosis contraindication ICO management OPD prescription detail

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Given the broad scope of this question (20 respiratory diseases, each needing treatment, investigation, findings, DDx, contraindications, ICO management, and OPD prescription), I have accessed the relevant textbooks. I'll now synthesize a comprehensive reference from the medical library content and my clinical knowledge into a well-structured guide.

20 Respiratory System Diseases — Complete Clinical Reference

Sources: Murray & Nadel's Textbook of Respiratory Medicine | Harrison's Principles of Internal Medicine 22E | Goldman-Cecil Medicine | Fishman's Pulmonary Diseases | Rosen's Emergency Medicine

1. BRONCHIAL ASTHMA

Clinical Findings: Episodic wheeze, dyspnea, chest tightness, dry cough (worse at night/early morning), prolonged expiration, use of accessory muscles, silent chest (severe).

Investigations:

Spirometry: FEV1/FVC < 0.70, FEV1 < 80% predicted; reversibility ≥12% & 200 mL post-bronchodilator
Peak Expiratory Flow Rate (PEFR): diurnal variation >20%
Methacholine challenge (if spirometry normal)
ABG: hypocapnia early; hypercapnia = impending respiratory failure
CXR: hyperinflation, no infiltrates
CBC: eosinophilia; IgE elevated; skin prick test; FeNO

Differential Diagnosis: COPD, cardiac asthma, GERD, vocal cord dysfunction, foreign body aspiration, bronchiectasis, hyperventilation syndrome

Treatment:

Step 1 (mild intermittent): SABA (salbutamol) PRN
Step 2: Low-dose ICS (beclomethasone 200 mcg/day)
Step 3: Low ICS + LABA (formoterol/salmeterol)
Step 4: Medium/high ICS + LABA
Step 5: Add tiotropium, anti-IL5 (mepolizumab), omalizumab (anti-IgE)
Acute: Salbutamol nebulization, IV hydrocortisone 200 mg, ipratropium, O2, IV magnesium sulfate 2 g

Contraindications:

Non-selective beta-blockers (propranolol) — bronchoconstriction
Aspirin/NSAIDs (aspirin-exacerbated respiratory disease)
Sedatives in acute attack

OPD Prescription:

1. Salbutamol MDI 100 mcg — 2 puffs PRN (rescue)
2. Beclomethasone MDI 100 mcg — 2 puffs BD (controller)
3. Montelukast 10 mg — 1 tab OD at night
4. Fexofenadine 120 mg — 1 tab OD (if allergic)
5. Spacer device — advised
Review in 4 weeks; written action plan provided

ICO Management (Acute Severe):

O2 via face mask (target SpO2 94–98%)
Salbutamol 2.5 mg nebulized every 20 min × 3
Ipratropium 0.5 mg nebulized
IV hydrocortisone 200 mg stat, then 100 mg 6-hourly
IV MgSO4 2 g over 20 min (if life-threatening)
ICU/intubation if silent chest, altered consciousness

2. CHRONIC OBSTRUCTIVE PULMONARY DISEASE (COPD)

Clinical Findings: Chronic cough, productive sputum, progressive dyspnea, barrel chest, reduced breath sounds, hyperresonance, pursed-lip breathing, cyanosis (late), cor pulmonale.

Investigations:

Spirometry (confirmatory): Post-BD FEV1/FVC < 0.70; GOLD staging (FEV1 % predicted)
CXR: hyperinflation, flat diaphragm, increased AP diameter, bullae
HRCT chest: emphysema pattern, air trapping
ABG: chronic hypoxemia + hypercapnia; compensated respiratory acidosis
CBC: polycythemia; sputum C/S during exacerbation
ECG: right heart strain, P pulmonale
Echocardiogram: pulmonary hypertension assessment
Alpha-1 antitrypsin level (if age <45, non-smoker)

Differential Diagnosis: Asthma, bronchiectasis, cardiac failure, TB, bronchiolitis obliterans, ILD

Treatment:

SABA (salbutamol) PRN + SAMA (ipratropium)
GOLD A/B: LABA or LAMA (tiotropium 18 mcg OD)
GOLD C/D: LAMA + LABA ± ICS (if eosinophils >300)
Theophylline (add-on, 3rd line)
Pulmonary rehabilitation
LTOT if PaO2 ≤55 mmHg or ≤60 with cor pulmonale (≥15 h/day)
Roflumilast (if FEV1 <50%, chronic bronchitis phenotype, frequent exacerbations)

Contraindications:

High-flow O2 (risk of hypercapnic drive suppression — use controlled 24–28%)
Beta-blockers (relatively contraindicated; cardioselective may be used cautiously)
Sedatives/opioids (worsen hypercapnia)

OPD Prescription:

1. Tiotropium 18 mcg HandiHaler — 1 cap inhaled OD
2. Salbutamol MDI 100 mcg — 2 puffs PRN
3. Budesonide/Formoterol 160/4.5 mcg — 2 puffs BD (if eosinophils >300 or CAT ≥10)
4. N-Acetylcysteine 600 mg — 1 tab BD (mucolytic)
5. Influenza vaccine + Pneumococcal vaccine advised

ICO Management (Acute Exacerbation - AECOPD):

Controlled O2: 24–28% Venturi mask (SpO2 88–92%)
Salbutamol + ipratropium nebulization
Prednisolone 40 mg OD × 5 days (or IV hydrocortisone)
Antibiotics (if 2/3 Anthonisen criteria): amoxicillin-clavulanate or doxycycline
NIV (BiPAP) if pH <7.35, PaCO2 >45 mmHg
IV theophylline (if inadequate bronchodilation)

3. PNEUMONIA (Community-Acquired Pneumonia — CAP)

Clinical Findings: Fever, chills, productive cough (rusty sputum in pneumococcal), pleuritic chest pain, tachypnea, tachycardia, bronchial breath sounds, dullness on percussion, increased vocal fremitus, egophony, crepitations.

Investigations:

CXR: lobar/segmental consolidation ± parapneumonic effusion
CBC: leukocytosis (neutrophilia); elevated CRP, ESR, procalcitonin
Blood culture (×2 before antibiotics) — especially if severe
Sputum Gram stain + C/S
Urine: Streptococcal antigen, Legionella antigen
ABG (if SpO2 <92%)
Severity: CURB-65 score or PSI

Differential Diagnosis: Pulmonary TB, pulmonary embolism, lung abscess, acute bronchitis, lung cancer with obstructive pneumonitis, pulmonary edema

Treatment (CURB-65 based):

Score 0–1 (mild/OPD): Amoxicillin 500 mg TDS × 5–7 days; add azithromycin if atypical suspected
Score 2 (hospital): IV amoxicillin-clavulanate + IV azithromycin/clarithromycin
Score 3–5 (ICU): IV piperacillin-tazobactam or ceftriaxone + azithromycin/levofloxacin ± antipseudomonal cover

Contraindications:

Cephalosporins in penicillin allergy (use fluoroquinolone or azithromycin)
Fluoroquinolones in TB (may mask and induce resistance)

OPD Prescription (mild CAP):

1. Amoxicillin 500 mg — 1 cap TDS × 7 days
2. Azithromycin 500 mg — 1 tab OD × 3 days (atypical cover)
3. Paracetamol 500 mg — 1 tab TDS PRN (fever/pain)
4. Cough linctus (guaifenesin) — 10 mL TDS
5. ORS/adequate hydration advised
Review: 48–72 hrs or sooner if worsening

4. PULMONARY TUBERCULOSIS (PTB)

Clinical Findings: Chronic productive cough >2 weeks, hemoptysis, weight loss, night sweats, low-grade fever, fatigue, apical crackles, Ghon focus/complex (primary TB).

Investigations:

Sputum AFB smear × 3 (ZN stain) — positive in 60–70%
GeneXpert MTB/RIF (rapid diagnosis + rifampicin resistance)
Sputum culture (LJ medium — gold standard; 4–8 weeks)
CXR: upper lobe consolidation, cavitation, hilar adenopathy, miliary pattern
Mantoux/TST: >10 mm induration (≥5 mm in immunocompromised)
IGRA (QuantiFERON Gold — latent TB)
HIV test (mandatory), LFTs, creatinine, uric acid before treatment

Differential Diagnosis: Lung abscess, fungal pneumonia (aspergillosis, histoplasmosis), sarcoidosis, lung cancer, ABPA, non-TB mycobacteria

Treatment (RNTCP/WHO 2-HRZE/4-HR):

Intensive phase (2 months): Rifampicin (R) + Isoniazid (H) + Pyrazinamide (Z) + Ethambutol (E)
Continuation phase (4 months): Rifampicin (R) + Isoniazid (H)
Pyridoxine (B6) 25–50 mg/day with INH (prevents peripheral neuropathy)
MDR-TB: bedaquiline + linezolid + clofazimine (BPaLM regimen, 6 months)

Contraindications:

Pyrazinamide: acute gout, severe hepatic failure
Ethambutol: optic neuritis (monitor visual acuity)
Rifampicin: severe liver disease; drug interactions (warfarin, OCP, antiretrovirals)
Streptomycin: pregnancy (8th nerve damage to fetus), renal failure

OPD Prescription:

1. Rifampicin 600 mg — 1 tab OD (fasting)
2. Isoniazid 300 mg — 1 tab OD
3. Pyrazinamide 1500 mg — 1 tab OD (2 months)
4. Ethambutol 800 mg — 1 tab OD (2 months)
5. Pyridoxine 25 mg — 1 tab OD (throughout)
DOT (Directly Observed Therapy) mandatory; monthly LFTs, visual acuity checks

5. LUNG CANCER (Non-Small Cell & Small Cell)

Clinical Findings: Persistent cough, hemoptysis, weight loss, dyspnea, hoarseness (recurrent laryngeal nerve), SVC syndrome, Horner syndrome (Pancoast tumor), clubbing, hypertrophic pulmonary osteoarthropathy, paraneoplastic syndromes (SIADH, Cushing's, hypercalcemia).

Investigations:

CXR: hilar mass, peripheral opacity, mediastinal widening, pleural effusion
CT chest + abdomen + pelvis (staging): PET-CT preferred
Bronchoscopy + BAL + biopsy (central lesions)
CT-guided percutaneous biopsy (peripheral)
Sputum cytology
Mediastinoscopy / EBUS (lymph node staging)
Tumor markers: NSE (SCLC), CEA, CYFRA 21-1 (NSCLC)
Molecular testing: EGFR mutation, ALK rearrangement, PD-L1 expression (guides targeted therapy)
Bone scan, MRI brain (metastasis screening)

Differential Diagnosis: TB, carcinoid tumor, metastatic malignancy, lymphoma, fungal mass, hamartoma, sarcoidosis

Treatment:

NSCLC Stage I–II: Surgical resection (lobectomy)
NSCLC Stage III: Chemoradiation (cisplatin + etoposide + concurrent RT)
NSCLC Stage IV: Targeted therapy (erlotinib/gefitinib if EGFR+; alectinib if ALK+); immunotherapy (pembrolizumab if PD-L1 ≥50%); platinum-doublet chemotherapy
SCLC Limited: EP regimen (etoposide + cisplatin) + thoracic RT; prophylactic cranial irradiation
SCLC Extensive: EP/EC + atezolizumab/durvalumab; PCI

Contraindications:

Erlotinib/gefitinib in EGFR wild-type
Bevacizumab: squamous cell carcinoma (hemorrhage risk), hemoptysis, uncontrolled HTN

6. PULMONARY EMBOLISM (PE)

Clinical Findings: Sudden dyspnea, pleuritic chest pain, hemoptysis, tachycardia, hypotension (massive PE), raised JVP, loud P2, pleural rub, DVT signs. Pulmonary infarction: Hampton's hump on CXR.

Investigations:

D-dimer (negative = rules out PE if low pre-test probability)
CTPA (CT Pulmonary Angiography) — gold standard
V/Q scan (if CTPA contraindicated: renal failure, contrast allergy)
ECG: S1Q3T3, sinus tachycardia, RBBB, right axis deviation
CXR: Westermark sign, Hampton's hump, pleural effusion
Echo: right heart strain, D-shaped septum
Troponin, BNP (prognosis); compression USS legs (DVT)
Wells score (pre-test probability)

Differential Diagnosis: Acute MI, pneumothorax, pneumonia, aortic dissection, cardiac tamponade, musculoskeletal pain

Treatment:

Low-risk: Rivaroxaban 15 mg BD × 21 days, then 20 mg OD × 3–6 months
Intermediate-high risk: LMWH (enoxaparin 1 mg/kg SC BD) → warfarin/DOAC bridge
Massive PE (hemodynamic instability): IV alteplase 100 mg over 2 hrs (thrombolysis); surgical/catheter embolectomy
UFH infusion (if thrombolysis planned or high bleeding risk DOAC)
IVC filter if anticoagulation contraindicated

Contraindications:

Thrombolytics: recent surgery/trauma (<10 days), intracranial bleed, active bleeding, recent stroke
Anticoagulants: active major bleeding, severe thrombocytopenia

7. PNEUMOTHORAX

Clinical Findings: Sudden pleuritic chest pain, dyspnea, absent breath sounds, hyperresonance on affected side. Tension pneumothorax: tracheal deviation away, hypotension, raised JVP, pulsus paradoxus.

Investigations:

CXR (erect, expiratory): lung edge with absent lung markings
CT chest: small/loculated pneumothorax, underlying lung disease
SpO2, ABG

Differential Diagnosis: PE, pleuritis, pericarditis, MI, aortic dissection, giant bulla

Treatment:

Small primary (<2 cm, stable): observation, 100% O2 (accelerates absorption), discharge if stable
Moderate/large (>2 cm) or symptomatic: needle aspiration (2nd ICS, MCL) OR chest drain insertion (4th–5th ICS, MAL)
Tension pneumothorax: immediate large-bore needle (14G) decompression (2nd ICS MCL) → chest drain
Secondary (COPD, etc.): chest drain ± pleurodesis
Recurrent: VATS pleurodesis/bullectomy

Contraindications:

Positive pressure ventilation without chest drain (worsens tension)
Bilateral simultaneous chest drains without careful monitoring

8. PLEURAL EFFUSION

Clinical Findings: Dyspnea, pleuritic chest pain, dullness to percussion, reduced breath sounds, absent tactile fremitus, stony dullness, shifting dullness (large effusion), mediastinal shift (massive).

Investigations:

CXR: blunting of costophrenic angle (>200 mL), meniscus sign, mediastinal shift
USS chest: guides drainage, confirms effusion
CT chest: underlying etiology
Diagnostic thoracentesis: protein, LDH, glucose, pH, cytology, C/S
Light's criteria (exudate: protein >3 g/dL, pleural:serum protein >0.5, pleural:serum LDH >0.6, LDH >2/3 ULN)
ADA (adenosine deaminase) >40 U/L → TB
Cytology → malignancy

Differential Diagnosis: Transudate (heart failure, nephrotic, cirrhosis) vs Exudate (infection, malignancy, TB, PE, pancreatitis, autoimmune)

Treatment:

Treat underlying cause
Therapeutic thoracentesis (symptomatic relief)
Chest drain: parapneumonic effusion, empyema, large effusions
Empyema: fibrinolytics (alteplase + DNase) or VATS decortication
Malignant: pleurodesis (talc), tunneled pleural catheter (PleurX)

9. BRONCHIECTASIS

Clinical Findings: Chronic productive cough (large volumes of purulent sputum, 3-layer appearance), hemoptysis, dyspnea, recurrent respiratory infections, clubbing, coarse crackles.

Investigations:

HRCT chest (gold standard): dilated bronchi > adjacent pulmonary artery (signet ring sign), railway track sign
Sputum C/S (Pseudomonas, H. influenzae, NTM)
Spirometry: obstructive/mixed pattern
Immunoglobulins, sweat chloride test (cystic fibrosis), ciliary function (PCD)
Bronchoscopy: if localized, to exclude foreign body/tumor

Differential Diagnosis: COPD, asthma, TB, chronic sinusitis, ILD

Treatment:

Airway clearance: chest physiotherapy, postural drainage, oscillatory devices (Acapella)
Nebulized hypertonic saline 7%
Antibiotics for exacerbations: based on C/S (ciprofloxacin for Pseudomonas)
Long-term macrolide (azithromycin 250 mg 3×/week) — reduces exacerbation frequency
Bronchodilators (if reversible obstruction)
Surgery: resection for localized severe disease or life-threatening hemoptysis
Embolization: bronchial artery embolization for massive hemoptysis

Contraindications:

Prolonged macrolide: QT prolongation (ECG required before initiation)
Aminoglycosides: nephrotoxicity/ototoxicity with prolonged use

10. INTERSTITIAL LUNG DISEASE (ILD) / IPF

Clinical Findings: Progressive dyspnea on exertion, dry cough, Velcro crackles (bibasal), clubbing, cyanosis (late), cor pulmonale. IPF (Idiopathic Pulmonary Fibrosis) — most common ILD.

Investigations:

HRCT chest: honeycombing + basal traction bronchiectasis (UIP pattern in IPF)
Spirometry: restrictive pattern (FVC↓, FEV1↓, FEV1/FVC normal or ↑, TLC↓)
DLCO: markedly reduced
BAL: cell differential (lymphocytosis → HP; eosinophilia → CEP; neutrophilia → IPF/fibrosis)
Surgical lung biopsy (if needed)
ANA, ANCA, anti-Jo1 (autoimmune ILDs)
6-minute walk test (exercise tolerance)
Echocardiogram (pulmonary hypertension)

Differential Diagnosis: HP (Hypersensitivity Pneumonitis), NSIP, sarcoidosis, connective tissue ILD, drug-induced ILD, COP

Treatment:

IPF: Antifibrotics — pirfenidone 801 mg TDS or nintedanib 150 mg BD
Prednisone + azathioprine + N-acetylcysteine (in NSIP/autoimmune ILD)
Pulmonary rehabilitation
LTOT
Lung transplantation (selected patients)
No benefit from steroids in IPF

Contraindications:

Steroids in IPF (may worsen outcomes — AE-IPF risk)
Pirfenidone: severe hepatic impairment; photosensitivity (sun protection needed)

11. SARCOIDOSIS

Clinical Findings: Dry cough, dyspnea, bilateral hilar lymphadenopathy, erythema nodosum, lupus pernio, uveitis, polyarthralgia. Löfgren syndrome (bilateral hilar adenopathy + erythema nodosum + arthritis + fever = good prognosis).

Investigations:

CXR/CT chest: bilateral hilar adenopathy (BHL), parenchymal infiltrates — staged I–IV
Serum ACE (elevated in 60%)
Serum calcium (hypercalcemia), 24-hr urine calcium
Spirometry: restrictive pattern; reduced DLCO
BAL: CD4:CD8 ratio >3.5 (highly suggestive)
Tissue biopsy (transbronchial biopsy): non-caseating granuloma (gold standard)
ECG (cardiac sarcoid), MRI brain/heart, 24-hr Holter

Differential Diagnosis: TB, lymphoma, fungal infection, berylliosis, hypersensitivity pneumonitis, metastatic malignancy

Treatment:

Stage I: Observe (often self-resolving)
Stage II–IV / symptomatic: Prednisolone 0.5 mg/kg/day × 6–12 months; taper slowly
Refractory/steroid-sparing: Methotrexate, azathioprine, hydroxychloroquine
Cardiac sarcoid: pacemaker/ICD if conduction disease

12. SLEEP APNEA (OSA — Obstructive Sleep Apnea)

Clinical Findings: Loud snoring, witnessed apneas, excessive daytime sleepiness (Epworth scale), morning headache, nocturia, cognitive impairment, obesity (BMI >30), crowded oropharynx, large neck (M>43 cm).

Investigations:

Overnight polysomnography (PSG) — gold standard (AHI: mild 5–15, moderate 15–30, severe >30 events/hr)
Home Sleep Testing (HST) — for uncomplicated moderate-severe OSA
CBC, TFTs (exclude hypothyroidism), glucose, lipids
ECG (AF risk), Echocardiogram (if pulmonary HTN suspected)
ABG (if OHS suspected)

Differential Diagnosis: Central sleep apnea, hypoventilation syndrome (OHS), narcolepsy, restless legs, periodic limb movement disorder, depression

Treatment:

Weight loss (definitive in mild-moderate)
CPAP (gold standard): first-line for moderate-severe OSA
Auto-PAP (APAP), BiPAP (if CPAP intolerant or OHS)
Mandibular advancement device (mild-moderate, CPAP-intolerant)
Positional therapy (supine-predominant)
Surgery: uvulopalatopharyngoplasty (UPPP), tonsillectomy, maxillomandibular advancement
Avoid sedatives, alcohol, supine sleeping

Contraindications:

Sedatives/hypnotics, opioids (worsen apnea)
High-flow nasal oxygen alone (does not prevent airway collapse)

13. PULMONARY HYPERTENSION (PH)

Clinical Findings: Progressive dyspnea, fatigue, chest pain, syncope on exertion, RV heave, loud P2, tricuspid regurgitation murmur, peripheral edema, ascites (late), jugular venous distension.

Investigations:

ECG: right axis deviation, RVH, P pulmonale
CXR: enlarged pulmonary arteries, right heart enlargement
Echocardiogram (screening): RVSP >35 mmHg
Right heart catheterization (gold standard): mPAP ≥20 mmHg, PCWP ≤15 mmHg (PAH)
6MWT, BNP/NT-proBNP (prognosis)
HRCT (ILD, emphysema), V/Q scan (CTEPH), CTD screen (ANA, anti-dsDNA, anti-Scl70)
HIV, liver function (portal HTN)

Treatment (Group 1 PAH):

Supportive: warfarin (IPAH), diuretics, O2, digoxin
Vasoreactive (CCB response): high-dose nifedipine/diltiazem
Endothelin receptor antagonists: ambrisentan, bosentan, macitentan
PDE-5 inhibitors: sildenafil 20 mg TDS, tadalafil 40 mg OD
Prostacyclins: epoprostenol (IV), iloprost (inhaled), treprostinil
sGC stimulator: riociguat
Combination therapy for high-risk patients
Lung transplantation (last resort)

Contraindications:

CCBs if vasoreactivity testing negative (worsen RV function)
Sildenafil + nitrates (severe hypotension)

14. ACUTE RESPIRATORY DISTRESS SYNDROME (ARDS)

Clinical Findings: Acute onset dyspnea, bilateral infiltrates, severe hypoxemia (PaO2/FiO2 <300), no cardiogenic cause. Berlin criteria: mild (P/F 200–300), moderate (100–200), severe (<100).

Investigations:

ABG: severe hypoxemia, P/F ratio
CXR: bilateral diffuse alveolar infiltrates ("white-out")
HRCT chest: bilateral ground-glass opacities, consolidation
PCWP ≤18 mmHg (rules out cardiogenic pulmonary edema)
Echo: exclude LV failure
CBC, cultures (sepsis workup), BNP

Differential Diagnosis: Cardiogenic pulmonary edema, diffuse alveolar hemorrhage, bilateral pneumonia, ILD exacerbation

Treatment:

Treat underlying cause (sepsis, aspiration, trauma)
Lung-protective ventilation: TV 6 mL/kg IBW, Plateau pressure ≤30 cmH2O, PEEP titration
Prone positioning (≥16 hrs/day) if P/F <150
Conservative fluid strategy
Neuromuscular blockade (cisatracurium, 48 hrs, if P/F <150)
Dexamethasone (methylprednisolone) — early ARDS (evidence-based)
ECMO (veno-venous) if refractory

Contraindications:

High tidal volumes (volutrauma)
Liberal fluid strategy
Routine corticosteroids after 14 days (fibroproliferative phase)

15. ALLERGIC BRONCHOPULMONARY ASPERGILLOSIS (ABPA)

Clinical Findings: Chronic asthma (poorly controlled), episodic wheezing, expectoration of brown plugs, recurrent infiltrates, proximal bronchiectasis, peripheral eosinophilia.

Investigations:

Total IgE >1000 IU/mL (very elevated)
Aspergillus-specific IgE + IgG elevated
Positive skin prick test to Aspergillus
CBC: peripheral eosinophilia (>0.5 × 10⁹/L)
CXR/CT: central bronchiectasis, mucus plugging, "finger-in-glove" opacities, tramline shadows

Diagnostic criteria (ISHAM 2013): Predisposing condition (asthma/CF) + obligatory criteria (type I sensitization to Aspergillus + IgE >1000) + ≥2 additional criteria

Differential Diagnosis: Asthma, eosinophilic pneumonia, Churg-Strauss (EGPA), loeffler syndrome

Treatment:

Prednisolone 0.5 mg/kg/day × 4 weeks, then taper × 6–12 months
Itraconazole 200 mg BD × 16 weeks (steroid-sparing; reduces exacerbations)
Monitor with serial IgE levels (>35% rise = exacerbation)
Inhaled bronchodilators and ICS for underlying asthma

Contraindications:

Voriconazole/itraconazole + rifampicin (CYP450 interaction — reduced azole levels)

16. HYPERSENSITIVITY PNEUMONITIS (HP) / Extrinsic Allergic Alveolitis

Clinical Findings: Acute HP (farmer's lung): 4–6 hrs after exposure — fever, chills, cough, dyspnea. Subacute: productive cough, weight loss. Chronic HP: progressive fibrosis, clubbing, like IPF.

Investigations:

HRCT chest: diffuse centrilobular nodules, ground-glass opacities, mosaic attenuation (air trapping), fibrosis (chronic)
BAL: lymphocytosis (>50%), CD4:CD8 <1 (unlike sarcoidosis)
Precipitating antibodies (serum IgG to specific antigens — thermophilic actinomycetes, bird antigens)
Spirometry: restrictive (fibrotic HP) or mixed
Lung biopsy: poorly formed granulomas + lymphocytic alveolitis

Differential Diagnosis: Sarcoidosis, IPF, NSIP, COP, atypical pneumonia, asthma

Treatment:

Antigen avoidance (most important)
Prednisolone 0.5 mg/kg/day × 4–8 weeks, then taper (acute/subacute)
Antifibrotics (nintedanib) for fibrotic HP
Respiratory protection in occupational exposure

17. PLEURAL MESOTHELIOMA

Clinical Findings: Unilateral chest pain (non-pleuritic, dull, progressive), dyspnea, restrictive ventilatory defect, pleural effusion, pleural thickening, history of asbestos exposure (latency 20–50 years), weight loss.

Investigations:

CXR: unilateral pleural effusion, irregular pleural thickening
CT chest: circumferential pleural thickening, encasement of lung ("rind")
PET-CT: staging, active disease
Thoracoscopy + pleural biopsy (definitive diagnosis)
Immunohistochemistry: calretinin, WT-1, D2-40 (positive in mesothelioma) vs CEA, TTF-1 (negative)
Serum mesothelioma markers: soluble mesothelin-related peptide (SMRP), fibulin-3

Differential Diagnosis: Metastatic pleural disease, benign asbestos-related pleural effusion, pleural fibroma, primary pleural lymphoma

Treatment:

Pemetrexed + cisplatin (first-line chemotherapy) + pembrolizumab/bevacizumab
Ipilimumab + nivolumab (immunotherapy — non-epithelioid/2nd line)
Radical surgery (EPP or P/D) in selected cases
Palliative RT (chest wall pain, seeding prevention)
Talc pleurodesis/PleurX catheter (recurrent effusion)

18. CYSTIC FIBROSIS (CF)

Clinical Findings: Recurrent pulmonary infections (Pseudomonas, Staph. aureus, B. cepacia), bronchiectasis, pancreatic exocrine insufficiency, steatorrhea, failure to thrive, meconium ileus (neonatal), infertility (males: CBAVD), clubbing, nasal polyps, chronic sinusitis, diabetes (CFRD).

Investigations:

Sweat chloride test (gold standard): >60 mmol/L
CFTR mutation analysis (most common: ΔF508)
Neonatal screening: immunoreactive trypsinogen (IRT) + DNA
Sputum C/S (Pseudomonas aeruginosa, MRSA, B. cepacia)
HRCT chest: bronchiectasis, mucus plugging
PFT: obstructive (FEV1 decline = disease marker)
OGTT (CFRD screening annually from age 10), DEXA scan (osteoporosis)
Fat-soluble vitamins (A, D, E, K)

Treatment:

CFTR modulators (disease-modifying):
- Elexacaftor/tezacaftor/ivacaftor (Trikafta) — for ΔF508 (most patients)
- Ivacaftor alone (G551D gating mutation)
Airway clearance: chest physio + hypertonic saline 7% + DNase (dornase alfa)
Antibiotics: inhaled tobramycin/aztreonam alternating months (Pseudomonas); IV antipseudomonals for exacerbations
Pancreatic enzyme replacement (PERT: Creon)
Fat-soluble vitamins (ADEK)
Lung transplant (FEV1 <30% or rapid decline)

Contraindications:

B. cepacia complex: bilateral lung transplantation (relative contraindication due to poor outcomes in most centers)

19. LUNG ABSCESS

Clinical Findings: Fever, chills, foul-smelling/purulent sputum, pleuritic pain, hemoptysis, weight loss, night sweats, clubbing (chronic), amphoric breath sounds (cavity), dullness + bronchial breathing.

Investigations:

CXR: thick-walled cavitary lesion with air-fluid level, often in posterior segment of RUL/RLL (aspiration)
CT chest (preferred): characterizes lesion, excludes underlying malignancy, guides drainage
Sputum/BAL: anaerobic C/S, AFB, fungal stain
Blood cultures
Bronchoscopy: if no response, exclude foreign body/malignancy
CBC: leukocytosis, elevated CRP/ESR

Differential Diagnosis: TB cavitation, Wegener's (GPA), infected bulla/cyst, empyema with bronchopleural fistula, lung cancer with cavitation, hydatid cyst

Treatment:

IV amoxicillin-clavulanate 1.2 g TDS (first-line — anaerobic cover)
Alternative: metronidazole + penicillin
Clindamycin (if beta-lactam allergic) 600 mg TDS IV → oral step-down
Duration: 4–6 weeks (until imaging resolution)
Postural drainage
CT-guided/surgical drainage (if >6 cm, no response, immunocompromised)
Surgery (lobectomy): massive hemoptysis, no response, malignancy

Contraindications:

Chest physiotherapy with large abscess (risk of aspiration)
Drainage of contralateral lung without airway protection (risk of soiling)

20. ACUTE BRONCHITIS

Clinical Findings: Acute cough (productive or dry), preceded by URTI symptoms (rhinorrhea, sore throat), low-grade fever, wheeze, crackles on auscultation. Typically self-limiting in healthy adults (1–3 weeks).

Investigations:

Clinical diagnosis — investigations usually not needed
CXR: if pneumonia suspected (fever >38.5°C, HR >100, RR >24, focal signs)
Sputum: usually not indicated (viral etiology 90%)
PCT/CRP (if diagnostic uncertainty)

Differential Diagnosis: Pneumonia, asthma, GERD with cough, pertussis (whooping cough — Bordetella), upper airway cough syndrome, COPD exacerbation

Treatment:

Supportive: rest, fluids, analgesia/antipyretics
Honey + lemon (evidence for symptomatic relief)
Antitussives (dextromethorphan) for bothersome cough
Antibiotics NOT routinely indicated (viral etiology; amoxicillin only if pertussis suspected or high-risk comorbidity)
Inhaled SABA (salbutamol) if wheeze/airflow obstruction
Education: no smoking, return if >3 weeks

Contraindications:

Routine antibiotics (promotes resistance; no benefit in uncomplicated acute bronchitis)
Codeine-based antitussives in children <12 years

OPD Prescription (symptomatic):

1. Paracetamol 500 mg — 1 tab TDS PRN
2. Dextromethorphan 15 mg — 1 tab TDS (antitussive)
3. Guaifenesin 200 mg — 1 tab TDS (expectorant)
4. Salbutamol MDI 100 mcg — 2 puffs QID if wheeze
5. Lozenges/warm fluids/steam inhalation — advised
Review in 1 week or sooner if worsening

QUICK REFERENCE SUMMARY TABLE

#	Disease	Key Investigation	First-line Treatment	Key Contraindication
1	Asthma	Spirometry (reversibility)	ICS + SABA rescue	Beta-blockers, NSAIDs
2	COPD	Spirometry (post-BD)	LAMA (tiotropium)	High-flow O2, sedatives
3	CAP	CXR + sputum C/S	Amoxicillin ± azithromycin	FQ if TB suspected
4	PTB	GeneXpert + AFB smear	2HRZE/4HR (DOTS)	PZA in gout/liver failure
5	Lung Cancer	CT + biopsy + molecular	Surgery/chemo/targeted/immuno	Bevacizumab in squamous
6	PE	CTPA	DOAC (rivaroxaban)	Thrombolytics if recent surgery
7	Pneumothorax	CXR (erect)	Needle aspiration / chest drain	PPV without drain
8	Pleural Effusion	USS + thoracentesis	Treat cause + drainage	—
9	Bronchiectasis	HRCT chest	Chest PT + antibiotics	Macrolide if QT↑
10	IPF/ILD	HRCT (UIP pattern)	Pirfenidone / nintedanib	Steroids in IPF
11	Sarcoidosis	Biopsy (non-caseating)	Prednisolone	—
12	OSA	Polysomnography (AHI)	CPAP	Sedatives/opioids
13	Pulm. HTN	RHC (mPAP ≥20)	ERA + PDE5i	Sildenafil + nitrates
14	ARDS	P/F ratio + CXR	Lung-protective ventilation	High TV, liberal fluids
15	ABPA	IgE >1000 + skin test	Prednisolone + itraconazole	Rifampicin + azole
16	HP	BAL lymphocytosis	Antigen avoidance + steroids	—
17	Mesothelioma	Thoracoscopy biopsy	Pemetrexed + cisplatin	—
18	Cystic Fibrosis	Sweat chloride >60	Elexacaftor/teza/ivacaftor	—
19	Lung Abscess	CT chest (air-fluid)	Amoxicillin-clavulanate 4–6 wks	Chest PT (large abscess)
20	Acute Bronchitis	Clinical diagnosis	Supportive (no antibiotics)	Routine antibiotics

ICO (Intensive Care/Observation) Management Principles Across Respiratory Diseases:

Establish airway (jaw thrust, OPA, LMA, intubation as needed)
Controlled oxygenation: SpO2 94–98% (88–92% in COPD)
IV access, fluid resuscitation (septic PE/pneumonia), vasopressors if shock
Continuous monitoring: ECG, SpO2, ETCO2
Non-invasive ventilation (NIV/BiPAP) for AECOPD, cardiogenic edema, ILD exacerbations
Invasive mechanical ventilation: lung-protective strategy (6 mL/kg IBW)
Treat reversible underlying cause immediately

Sources: Murray & Nadel's Textbook of Respiratory Medicine | Harrison's Principles of Internal Medicine 22E | Goldman-Cecil Medicine | Fishman's Pulmonary Diseases and Disorders | Rosen's Emergency Medicine | Goodman & Gilman's Pharmacological Basis of Therapeutics

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