A female presents with history of progressive breathlessness. Histology shows heterogenous patchy fibrosis with several fibroblastic foci. The most likely diagnosis is -

Ref:pathologic basis of disease (Robbins and cotran)7th edition, page no.729 Morphology of usual interstitial pneumonia Grossly, the pleural surfaces of the lung are cobblestoned owing to the retraction of scars along interglobular septa. The cut surface shows fibrosis (firm, rubbery white areas) of the lung parenchyma with lower lobe predominance and a distinctive distribution in the subpleural regions and along the interlobular septa. Microscopically, the hallmark of the UIP is patchy interstitial fibrosis , which varies in intensity and with time. The earluest lesions contain exhuberent fibroblastic proliferation and appear as fibroblastic foci . With time these areas become more collagenous and less cellular. The dense fibrosis causes collapse of alveolar walls and formation of cystic spaces lined by hyperplastic type II pneumocytes or bronchi olar epithelium (Honeycomb fibrosis) Clinical ccourse UIP begins insidiously, with gradually increasing dyspnea and dry cough. Most patients are 40 to 70 years old at the time of presentation . Hypoxaemia, cyanosis, and clubbing occur late in the course. The progression in an individual patient is unpredictable.