Monday, September 18, 2017

Interstitial Lung Disease

This post is derived from notes I took during training. Any images are copyright their respective owners.

Interstitial Lung Disease

  • Questions to ask
    • volumes reduced (fibrotic) vs. increased (airways disease)
    • distribution upper (trapped inhaled particulates) vs. lower (blood, lymphatic flow)
    • central vs. peripheral
    • centrilobular vs. septal
  • Interstitial disease
    • All tend to be related to smoking
    • causes peribronchial cuffing, which looks the same as bronchial wall thickening
  • Nonspecific Interstitial Pneumonia (NSIP)
    • Pathophysiology: homogeneous interstitial inflammation, many started as organizing pneumonia. Many etiologies, including connective tissue disease (*except* rheumatoid arthritis (RA))
    • Findings: lower lobe predominance. Subpleural, symmetric distribution of lower lobe patchy ground-glass opacities (GGO) - dominant feature with reticular opacities and limited traction bronchiectasis.

  • Usual Interstitial Pneumonia (UIP)
    • S l o w l y develop dyspnea, also associated with aspiration
    • Pathophysiology: the radiographic finding consistent with clinical syndrome of Idiopathic pulmonary fibrosis (IPF) - see temporal & geographic heterogeneity with fibroblast foci. For connective tissue disease, only RA gives this pattern.
    • Volume loss predominates fibrosis → honeycombing (dilated respiratory bronchioles) is collapse, not fibrosis
    • Findings: lower lobe peripheral honeycombing with spatial/temporal heterogeneity
    • Prognosis: 50% mortality at 3 years; biopsy has high mortality rate
  • Acute Interstitial Pneumonia (AIP; aka Hamman-Rich, ARDS)
    • Diffuse alveolar collapse with areas of sparing (possibly representing areas of arterial thrombosis) causing reduced volumes over rapid course
    • Treatment: Vent on PEEP mode to keep alveoli open
  • Constrictive bronchiolitis (Bronchiolitis obliterans)
    • Cough, dyspnea, malaise. Radiographically occult usually, may show air trapping/mosaic attenuation
    • Causes: diverse inhalational causes (e.g. Iraq lung, popcorn oil, graft-vs-host disease)
    • DI: hyperinflation, discrete nodules, mosaicism
  • Cryptogenic organizing pneumonia (COP)
    • Organization -  histologically, the incorporation of alveolar material into the interstitial wall by fibroblasts, seen in many processes
    • Findings: Peripheral consolidations or nodules along bronchovascular bundles with surrounding halo of consolidation (atoll / reverse halo sign - nonspecific), air bronchograms, and sparing of peripheral lung
    • 80% likely old infections with progressive scarring
  • Smoking related lung disease
    • Respiratory bronchiolitis (RB)
    • Respiratory bronchiolitis - Interstitial Lung Disease (RB-ILD)
      • Macrophages in interstitium causing GGO/nodules in slightly upper > lower lobes
    • Desquamative interstitial pneumonia (DIP)
      • Demographics: age 30-60s, M:F 2:1
      • Pathophysiology: Misleading name because no desquamation of alveolar epithelium present, but rather cells in alveolar space are pigment laden macrophages, thought to represent end-stage of RB-ILD
      • Findings: GGO and alveolar opacities, lower lobe predominant, ground glass
      • Treatment: steroids
  • Scleroderma
    • Progressive systemic sclerosis, esophageal involvement (patulous esophagus) (80%), cardiac involvement (40%),
    • CXR: fibrosis in lower lobes
    • CT: NSIP >> UIP pattern (4:1)
    • Prognosis: associated with increased lung adenocarcinoma
  • Eosinophilic Pneumonia (EP)
    • Can be secondary to unknown causes (Loeffler pneumonia, Acute EP, Chronic EP) versus secondary to known cause (drugs, fungal, parasitic infections)
    • Findings:
      • Simple / Loeffler: Peripheral ground glass opacities with interlobular septal thickening (ie reverse / photographic negative of pulmonary edema, upper lobe predominance. Positive blood eosinophils
      • Acute EP: bilateral GGO and interlobular septal thickening
      • Chronic EP: homogeneous peripheral airspace consolidation (reverse bat-wing pattern). Differential diagnosis: Churg-Strauss
    • Treatment: Steroids (good response)



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