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Nonspecific interstitial pneumonia (NSIP) is a distinct clinicopathologic form of interstitial lung disease (ILD), characterized histologically by uniform interstitial inflammation and/or fibrosis and radiologically by ground-glass opacities with basal predominance, often sparing the subpleural regions.

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Unlike UIP, NSIP lacks honeycombing and shows temporal uniformity in pathology.

Etiology

Clinical associations:

Context	Frequency
Connective tissue disease (CTD)	Most common (especially systemic sclerosis, dermatomyositis, Sjögren syndrome)
Drug-induced ILD	e.g., amiodarone, methotrexate
Idiopathic NSIP	~20–40% of NSIP cases
HIV-associated ILD	Less common

Clinical Features

Demographics:

Women > men; often middle-aged

Presentation:

Symptoms: Insidious dyspnea, dry cough, fatigue
Disease course:
- Cellular NSIP: Favorable prognosis with immunosuppression
- Fibrotic NSIP: May be slowly progressive, but better than UIP

Pulmonary function test (PFTs):

Restrictive pattern (↓TLC, ↓DLCO)

Radiology

HRCT features

Feature	Description
Distribution	Basal and peripheral lung predominance, often symmetrical
Ground-glass opacities	Diffuse or patchy, typically dominant in early disease
Reticulations	Fine linear opacities may be seen overlaying GGO
Subpleural sparing	Characteristic feature helping differentiate from UIP
Traction bronchiectasis	May be present, particularly in fibrotic NSIP
Honeycombing	Absent or minimal, distinguishing from UIP

Subtypes on imaging: