A 45-year-old woman with systemic sclerosis presents with progressive dyspnea and a restrictive pattern on pulmonary function tests. High-resolution computed tomography (HRCT) of the chest shows bilateral, predominantly basilar reticular opacities with traction bronchiectasis. Which of the following is the most likely diagnosis?

Explanation

## Diagnosis: UIP Pattern in Systemic Sclerosis ### Clinical Context The patient has systemic sclerosis (scleroderma) with progressive dyspnea and a restrictive pattern on PFTs — classic features of pulmonary fibrosis. HRCT findings are key to diagnosis. ### HRCT Features of UIP Pattern **Key Point:** The combination of bilateral, basilar-predominant reticular opacities WITH traction bronchiectasis is pathognomonic for UIP pattern. | Feature | UIP Pattern | NSIP Pattern | Organizing Pneumonia | AIP Pattern | |---------|-------------|--------------|----------------------|-------------| | **Distribution** | Basilar, peripheral | Basilar to mid-zone | Patchy, random | Diffuse | | **Reticular opacities** | Prominent | Mild to moderate | Absent | Absent | | **Traction bronchiectasis** | Present | Absent/minimal | Absent | Absent | | **Honeycombing** | Common | Rare | Absent | Absent | | **Consolidation** | Minimal | May be present | Prominent | Prominent | | **Associated with SSc** | Yes (most common) | Yes | Rare | No | ### Why UIP in Systemic Sclerosis? **High-Yield:** Systemic sclerosis is the connective tissue disease MOST strongly associated with UIP pattern (present in ~70% of SSc-ILD cases). The basilar and peripheral distribution with traction bronchiectasis is virtually diagnostic. **Clinical Pearl:** Traction bronchiectasis occurs because fibrotic remodeling pulls open the small airways — this finding essentially rules out organizing pneumonia and AIP, which do not cause architectural distortion. ### Pathophysiology In UIP, there is heterogeneous lung fibrosis with: 1. Microscopic honeycombing (cystic spaces lined by bronchiolar epithelium) 2. Fibroblast foci (active fibrosis) 3. Architectural remodeling → traction bronchiectasis 4. Basilar and peripheral predominance ### Prognosis and Management **Key Point:** UIP pattern in SSc carries a worse prognosis than NSIP. Antifibrotic therapy (pirfenidone, nintedanib) is indicated for progressive disease. [cite:Harrison 21e Ch 297]