Nonidiopathic Interstitial Pulmonary Fibrosis (Non-IPF): A Review of Etiologies, Pathophysiology, Diagnosis and Management

Nonidiopathic interstitial pulmonary fibrosis (non-IPF) encompasses a diverse spectrum of interstitial lung diseases characterized by inflammation and progressive fibrosis of the pulmonary interstitium, distinguished from idiopathic pulmonary fibrosis by the identification of a specific underlying cause. This review provides a comprehensive, academically rigorous examination of non-IPF, addressing its complex etiological landscape—including occupational and environmental exposures, drug-induced lung toxicity, connective tissue diseases, and systemic illnesses—each of which triggers a common pathogenic cascade of epithelial injury, inflammatory activation, and aberrant fibroproliferative repair mediated centrally by transforming growth factor-beta (TGF-β). Epidemiological data demonstrate a modest male predominance and peak incidence in the fifth to sixth decades of life, though considerable variation exists across etiologic subtypes. The diagnostic evaluation requires systematic integration of thorough occupational and medication histories, serological testing for autoimmune markers, high-resolution computed tomography (HRCT) findings—ranging from centrilobular nodules in hypersensitivity pneumonitis to honeycombing in end-stage disease—and, when indicated, histopathological examination via bronchoalveolar lavage, transbronchial biopsy, or surgical lung biopsy. Pulmonary function testing typically reveals a restrictive ventilatory defect with diminished diffusing capacity for carbon monoxide (DLCO). Management strategies encompass supportive measures (smoking cessation, vaccination, pulmonary rehabilitation, supplemental oxygen), etiology-specific interventions (corticosteroids, immunosuppressive agents, antigen avoidance), and, in progressive or severe cases, antifibrotic therapy or lung transplantation. Acute exacerbations, which carry high mortality rates approaching 100% in certain etiologies, require prompt recognition and aggressive immunosuppression. Given the diagnostic complexity and therapeutic implications, multidisciplinary team evaluation—integrating pulmonology, rheumatology, radiology, and pathology—substantially improves diagnostic accuracy and alters management in a majority of cases. Early diagnosis, identification of reversible causes, and coordinated interprofessional care remain the cornerstones of optimizing outcomes in this challenging group of disorders.