L29 Diffuse parenchymal lung disease (part I)

Basic alveolar anatomy

• Type I pneumocytes
• ->95% of alveolar surface area
• -thin, limited organelles
• -minority of alveolar cell population (?)
• -primary role: gas exchange
• -some ion exchange, regulation of fluid
• -susceptible to injury
• -unable to replicate

• Type II pneumocytes
• -Cuboidal
• -Majority of alveolar cell population (?)
• -primary role: surfactant production, fluid balance, stem cells for type I
• -lamellar bodies
• -replicate on demand
• -differentiate to replace injured type I cells

• 1. Diffusion gradient from alveolus to capillaries
• -P_AO2 = FiO₂*(P_atm - P_H2O) - (P_aCO₂/RQ)

• 2. Time for diffusion
• -typically requires ~0.25 seconds
• -capillary travel time ~0.75 seconds

• 3. Alterations of parenchyma have variable effects on oxygenation
• -increased diffusion time (typically insignificant; time remains below 0.75sec)
• -V/Q mismatching (always important)

• Destruction and distortion of the parenchymal anatomy
• Thickening of alveolar/capillary interface
• infiltration with immune cells
• alveolar filling
• bronchialar destruction or narrowing
• granulomas
• fibroblastic foci
• traction bronchiectasis
• fibrosis and honeycombing

• Autoimmune disease
• inhaled toxins or particulates
• drug-induced
• radiation-induced
• hormonal contributions
• associations with smoking
• idiopathic

• "classic" CT for parenchymal disease
• (i.e. pulmonary fibrosis)
• -some cystic changes
• -honeycombing
• -ground glass

• Compliance is the change in volume for a given change in pressure
• C=ΔV/ΔP
• parenchymal lung disease decreases lung compliance
• 
• increased effort (pressure) to fill lung to same volume --> Sx

• VARIABLE SX:
• -Dry cough
• -Shortness of breath
• -Shallow breathing
• -Swelling in ankles (R heart failure)
• -Syncope
• -asymptomatic (incidental finding on CXR)
• -Acute respiratory decompensation

• Exam findings:
• -Dry crackles ("Velcro" crackles)
• -Clubbing
• -Enhanced or split P2
• -Hypoxemia (especially with exertion)
• -Cachexia --increased work of breathing
• -Rheumatologic findings (arthritis, dermatitis, myositis, joint deformities)

• May find restrictive, obstructive, or combined pattern
• -Restriction is the most common pattern

• Reduced DLCO "out of proportion" with volumes
• -i.e. vital capacity ~70%, and DLCO ~30%

may find hypocapnia and hypoxemia

• Oxygen deseaturation with exertion is very common
• -V/Q mismatching
• -+/- impaired diffusion

Chronic inhalation of small particulates that deposit into smallest airways, alveoli

Disease is caused by immune system reaction to the accumulated particulates (i.e. alveolar macrophages)

• Tx: Avoidance, protective equipment
• -most industries now regulate exposure and require protective equipment

**Predisposition for pulmonary infections, especially Mycobacteria

• Chronic inhalation of very fine silicates (quartz)
• -sandblasters, miners, demolition, sanders

• Pathophysiology:
• -engulfed by alveolar macrophages
• -activation, destruction, re-engulfment cycle

Presentation: progressive parenchymal destruction

• Simple silicosis: small nodules on imaging
• 

• Complicated silicosis: coalescence of nodules, extensive fibrosis, cavities, ...
• 
• -demonstrates volume loss: R mainstem bronchi is higher than it should be

• Coal dust exposure
• Fibrous and emphysema seen in respiratory bronchioles
• Classifications: simple vs complicated
• Coal macules seen on pathology

Derivative of silica: straight, sharp, crystalline fibers

-Chronic exposure: insulation, shipworkers, pipefitters, break pads, Turkey! (NAVY)

• Deposition of fibers into respiratory bronchioles and alveoli
• -engulfment by macrophages...
• -Alveolitis, peribronchial fibrosis, subpleural cysts
• -Ferruginous bodies: Asbestos fibers coated in iron/protein complex by alveolar macrophages:
• 

• Pleural disease is common
• -Benign asbestos pleural effusion (BAPE)
• -Calcified pleural plaques (calcified lesions mostly benign) ... easy to see on CT
• 

• Associated with neoplasia:
• -Adenocarcinoma (especially increased risk when combined with smoking)
• -Mesothelioma (less common)

• Asbestosis
• -Fibrotic, destructive process, which can lead to progressive symptoms, disability or death

• Asbestos exposure along:
• -may find calcified nodes, effusions, or pleural plaques
• -fibrotic parenchymal changes are ABSENT

• Chronic exposure to beryllium dust
• -Electronic industry, military jet pilots or mechaniccs, aerospace workers, nuclear weapons

Clinically may mimic sarcoidosis

• Dx: Beryllium Lymphocyte Proliferation Test (BeLPT)
• -Measures response of pt's lymphocytes to beryllium exposure
• -Pts with berylliosis will show hypersensitive (T cells)
• -68% sensitive; 97% specific

• Collection of parenchymal diseases that are characterized by extrinsic allergic alveolitis
• -Robust immunologic reaction to inhaled organic matter

• *typically improves with avoidance
• -pts often asked to change habits to see test exposures

-Type III or Type IV hypersensitivity reaction

• Acute:
• -Sx within hrs
• -fever, chills, dyspnea, cough
• -May mimic pneumonia

• Subacute:
• -similar to acute, slower onset and less severe

• Chronic: Most common
• -Progressive to fibrosis, permanent disease
• -Historical link may be difficult to find

• Dx: 
• -History
• Pathology: Noncaseating granulomas
• 
• -cholesterol clefts
• 
• -Foamy macrophages

• Radiography:
• -infiltrates seen along the bronchovascular bundles
• -fibrosis and honeycombing when advanced or chronic
• 

• Bird fancier's lung
• Hot tub lung
• Farmer's lung
• Crack lung
• Maltworker's lung
• Popcorn worker's lung
• Penguin humidifier lung
• Cheese-washer's lung
• Japanese summer house hypersensitivity pneumonitis
• Wine-grower's lung
• ...