Nonspecific Interstitial Pneumonia (NSIP)
Nonspecific interstitial pneumonia (NSIP) is the type of interstitial lung disease that characteristically spares the pleura, with subpleural sparing serving as a key distinguishing feature from usual interstitial pneumonia (UIP). 1
Radiologic Features of NSIP
The most common HRCT finding in NSIP is bilateral ground-glass opacity, occurring in the majority of cases 1. However, the defining characteristic that answers your question is:
- Subpleural sparing is a helpful distinguishing feature that differentiates NSIP from UIP/IPF, which typically shows peripheral and subpleural predominance 1
- Irregular reticular opacities with traction bronchiectasis and bronchiolectasis occur in approximately 75% of cases 1
- Honeycombing is sparse or absent at presentation, though it may increase during follow-up 1
- When present, the disease shows a peribronchovascular predominance with characteristic subpleural sparing 1
Clinical Context
NSIP can occur as an idiopathic condition but also appears in several secondary settings that must be excluded 1:
- Collagen vascular disease (CVD)
- Hypersensitivity pneumonitis (HP)
- Drug toxicity
- Familial pulmonary fibrosis
Multidisciplinary discussion is especially important to establish the diagnosis of idiopathic NSIP and exclude these secondary causes 1.
Histologic Pattern
The histologic features show varying amounts of interstitial inflammation and fibrosis with a uniform appearance, which contrasts with the patchy, heterogeneous pattern of UIP 1. Most cases demonstrate a predominantly fibrotic pattern with rare cases of isolated cellular NSIP 1.
Contrast with UIP/IPF
Unlike NSIP, UIP/IPF characteristically shows:
- Peripheral and subpleural predominance (not sparing) 2
- Basal distribution of reticular changes 2
- Subpleural honeycombing 1
This subpleural distribution in UIP is the opposite of the subpleural sparing seen in NSIP, making this distinction clinically critical 1.
Prognosis
The prognosis of NSIP is variable but generally better than IPF 1. Some patients improve, others remain stable or improve on treatment, but some evolve to end-stage fibrosis 1.