A 34-year-old non-smoking woman presents with progressive dyspnea over 6 months. HRCT shows bilateral ground-glass opacification with lower lobe predominance and subpleural sparing. PFTs show restriction with DLCO 48% predicted. ANA 1:320 (speckled pattern), anti-Scl-70 positive. The most likely underlying ILD pattern is:

• A Usual interstitial pneumonia (UIP)
• B Nonspecific interstitial pneumonia (NSIP) ✓
• C Desquamative interstitial pneumonia (DIP)
• D Respiratory bronchiolitis-ILD (RB-ILD)

Explanation

NSIP is the most common ILD pattern in connective tissue diseases, particularly systemic sclerosis (anti-Scl-70/anti-topoisomerase-I positive), polymyositis-dermatomyositis and Sjögren's syndrome. HRCT in NSIP shows bilateral ground-glass opacification with lower lobe predominance and a characteristic subpleural sparing, distinguishing it from UIP (which shows subpleural honeycombing). DIP and RB-ILD are smoking-related ILDs and would be unusual in a non-smoker with CTD serology.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.