Nonspecific Interstitial Pneumonia
Definition
- Idiopathic interstitial lung injury demonstrating temporal uniformity and lacking diagnostic features of other diseases
Alternate/Historical Names
- NSIP
Diagnostic Criteria
- Clinical
- Insidious onset of dyspnea, cough, fatigue
- Mean age 40-50, may be seen in children
- Pulmonary function tests: restrictive with decreased diffusing capacity
- Generally less severe than UIP
- Overall 80=90% 5 year survival
- Responds to steroids
- High resolution computed tomography (HRCT)
- Predominantly ground glass opacities
- Changes bilateral, predominantly basal and peripheral
- Reticular, linear patterns may also be seen in 50%
- Focal honeycombing only seen in occasional cases
- Histopathologic features
- Changes in a given case are temporally uniform
- Interstitial inflammation ranges from mild to moderate
- Lymphoid follicles frequently present
- Type II pneumocyte hyperplasia
- Scant to dense interstitial fibrosis
- Generally preserves lung architecture
- EVG may be useful
- Honeycomb change is seen only in occasional cases and is not predominant
- Air spaces may be enlarged
- Traction bronchiolitis may be seen
- Bronchiole surrounded by fibrosis and larger than adjacent muscular artery
- Has been separated into two types
- Cellular type
- Changes are predominantly cellular, with scant fibrosis
- Better prognosis
- Fibrotic type
- Changes are predominantly fibrotic, with less cellularity
- NSIP is a diagnosis of exclusion
- The following features should not be seen
- Granulomas or giant cells
- Bronchiolocentric distribution
- Acute lung injury pattern / hyaline membranes
- More than rare eosinophils
- Evidence of infection
- Some features of other types of interstitial lung disease may be seen to a limited extent, but do not predominate
- Bronchiolitis obliterans / organizing pneumonia
- Desquamative interstitial pneumonia
- Focal fibroblastic foci typical of UIP
- Honeycomb pattern typical of UIP
- Discordant features may be seen (UIP on one biopsy, NSIP on another)
- Behaves as UIP
- Multiple biopsies are recommended, if possible
- The following must be ruled out in every case
- Collagen vascular disease
- Drug reaction
- Chronic hypersensitivity pneumonitis
- Giant cells and or granulomas
- Predominantly bronchiolocentric distribution
- Immunodeficiency related changes
- Infection
- Acid fast and fungal stain should be performed in every case
- Slowly resolving acute interstitial pneumonia
- Sampling error (see Discordant above)
Gerald J Berry MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
