A 52-year-old woman with systemic sclerosis presents with progressive dyspnea over 6 months. HRCT chest shows bilateral lower lobe predominant reticular opacities with traction bronchiectasis and minimal honeycombing. Which of the following is the most likely diagnosis?

## Diagnosis: Non-Specific Interstitial Pneumonia (NSIP) ### Clinical Context The patient has systemic sclerosis (SSc), a connective tissue disease with a high propensity for interstitial lung disease (ILD). The HRCT findings and clinical presentation are classic for NSIP, which is the most common ILD pattern in SSc. ### HRCT Features of NSIP **Key Point:** NSIP is characterized by: - Bilateral, symmetric reticular opacities (ground-glass or fine reticular pattern) - **Lower lobe predominance** (distinguishes it from UIP, which is basilar) - Traction bronchiectasis (bronchial dilation due to fibrosis) - **Minimal to absent honeycombing** — this is critical; honeycombing suggests UIP - Absence of subpleural/paraseptal distribution ### Comparison with UIP | Feature | NSIP | UIP | |---------|------|-----| | Honeycombing | Minimal/absent | Prominent | | Traction bronchiectasis | Present | Present | | Distribution | Diffuse, lower lobe | Basilar, subpleural | | Prognosis | Better | Worse | | SSc association | Most common | Less common | | Ground-glass | Prominent | Less prominent | **High-Yield:** In SSc-ILD, NSIP is found in ~60% of cases; UIP in ~20%. The presence of traction bronchiectasis WITHOUT honeycombing strongly favors NSIP. ### Why Lower Lobe Predominance Matters Both NSIP and UIP show lower lobe involvement, but UIP is **subpleural and basilar** with dense honeycombing. NSIP is more diffuse and uniform, with lower lobe predominance but without the architectural distortion of honeycombing. **Clinical Pearl:** NSIP has a better prognosis than UIP (median survival ~10–15 years vs. 3–5 years), which is clinically relevant for counseling SSc patients. ### Why Organizing Pneumonia? OP presents with consolidations and bronchiolitis obliterans pattern, NOT reticular opacities. It is typically associated with acute/subacute presentation and responds well to steroids — not the chronic progressive course here. ### Why Acute Interstitial Pneumonia? AIP is a fulminant, rapidly progressive condition with diffuse alveolar damage. It presents acutely (days to weeks) with respiratory failure, NOT a 6-month progressive course. HRCT shows diffuse ground-glass opacities and consolidation, not the organized reticular pattern seen here. [cite:Robbins 10e Ch 15]