Acute Interstitial Pneumonia - Diffuse Alveolar Damage
Definition
- Acute onset lung disease characterized by diffuse hyaline membrane formation followed by organization
Alternate/Historical Names
- Adult respiratory distress syndrome (clinical term for disease with this pattern)
Diagnostic Criteria
- Diffuse alveolar damage (DAD) is a pattern that has many causes including
- Infection, aspiration, shock, toxins, burns, transfusions and drugs
- When idiopathic, it is termed acute interstitial pneumonia (AIP)
- Both idiopathic and secondary DAD share an acute onset and poor prognosis
- Roughly 50% mortality in six months
- Clinical
- Sudden onset of dyspnea, cough over 1-2 weeks
- Occasionally subacute
- May occur at any age
- Sudden onset of dyspnea, cough over 1-2 weeks
- High resolution computed tomography (HRCT)
- Consolidation (early phase) developing into bilateral diffuse ground glass opacities
- Late phase may show cyst formation or diffuse honeycombing
- Histopathologic features
- Changes in first week are exudative
- Necrosis of alveolar lining cells with extravasation of fibrin
- Prominent, diffuse hyaline membranes in alveolar lumens
- Intra-alveolar balls of fibrin may be seen in acute fibrinous and organizing pneumonia variant, see below
- Fibroproliferative organizing phase follows in air spaces and interstitium
- Loose edematous fibroblastic tissue
- Little dense collagen deposition
- Hyaline membranes are resorbed by organization
- Fragments may remain in lumens and incorporated into interstitium
- Loose edematous fibroblastic tissue
- Late scarring phase
- Scarring may result in diffuse honeycomb change
- Alveoli lined by reactive alveolar lining cells with hobnail appearance
- Mitotic figures and marked reactive atypia may be seen
- Squamous metaplasia of bronchiolar and adjacent air spaces is frequent
- Mitotic figures and marked reactive atypia may be seen
- Mild to moderate interstitial infiltrate of plasma cells, lymphocytes
and neutrophils
- Eosinophils infrequent
- Organizing thrombi may be seen in small to medium sized pulmonary arteries
- Changes in first week are exudative
- DAD pattern may occur in the setting of acute exacerbation of a chronic interstitial lung disease such as UIP
- Underlying architectural changes such as peripheral honeycombing may help identify the diagnosis
- Clinical or radiographic history of pre-existing pulmonary disease is very helpful
- Acute Fibrinous and Organizing Pneumonia has been proposed as a variant
(Beasley 2002)
- Patchy involvement of alveoli by balls of fibrin
Gerald J Berry MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
