Symmetric basal ground-glass and reticulation with traction bronchiectasis and immediate subpleural sparing, little or no honeycombing — the NSIP pattern points to connective tissue disease or hypersensitivity until proven otherwise.
Orient first
- NSIP is the commonest ILD pattern in connective tissue disease (systemic sclerosis, myositis/antisynthetase).
- Subpleural sparing and the absence of honeycombing separate it from UIP.
- Fibrotic NSIP and fibrotic HP overlap — look for mosaic attenuation and air trapping.
Acquire the study
- High-resolution CT chest: thin sections (≤ 1.25 mm), supine inspiratory, prone images for the dependent lung, expiratory images for air trapping.
The manoeuvre
- Lung window: basal-predominant ground-glass and fine reticulation; symmetry.
- Subpleural sparing on axial slices in the posterior lower lobes.
- Traction bronchiectasis extent; honeycombing present or absent.
- Prone images: dependent opacity that persists = real disease.
- Oesophageal dilatation (systemic sclerosis); expiratory air trapping (HP).
What confirms it
- A compatible pattern in the multidisciplinary discussion with serology.
What licenses you to exclude it
- Honeycombing with a subpleural basal gradient favours UIP.
The classic misread
- Calling dependent atelectasis NSIP without prone images.