A 55-year-old woman non-smoker develops progressive breathlessness and dry cough. HRCT shows bilateral, basal, subpleural reticular opacities with honeycombing and traction bronchiectasis. Surgical lung biopsy shows a heterogeneous pattern with areas of dense fibrosis, fibroblastic foci, and normal lung alternating in a temporal and spatial heterogeneity. What is the WHO histological pattern and associated diagnosis?

• A Non-specific interstitial pneumonia (NSIP) pattern — temporally uniform fibrosis, associated with CTD and better prognosis than IPF
• B Desquamative interstitial pneumonia (DIP) pattern — diffuse macrophage accumulation in alveolar spaces, strongly linked to smoking
• C Organising pneumonia (OP) pattern — patchy Masson bodies (plugs of fibroblastic tissue in alveolar ducts) with excellent steroid response
• D Usual interstitial pneumonia (UIP) pattern — this is the histological correlate of idiopathic pulmonary fibrosis (IPF) when secondary causes are excluded ✓

Explanation

The UIP (usual interstitial pneumonia) pattern is defined by spatial and temporal heterogeneity — dense fibrosis with architectural distortion/honeycombing in the basal subpleural zones, fibroblastic foci (zones of active fibrosis at the advancing edge), alternating with areas of less affected or normal lung. This heterogeneous patchwork is the histological sine qua non of UIP, distinguishing it from NSIP (which is temporally uniform — all areas equally fibrotic) and OP (which shows Masson bodies in air spaces). When secondary causes (CTD, drugs, hypersensitivity pneumonitis) are excluded, UIP pattern = IPF. IPF progresses relentlessly with a median survival of 3–5 years; anti-fibrotic therapy (pirfenidone, nintedanib) slows progression.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.