Chronic progressive fibrosing interstitial pneumonia of unknown cause with UIP pattern.
Also known as: IPF, idiopathic pulmonary fibrosis, UIP, usual interstitial pneumonia
Overview
Specific form of chronic, progressive fibrosing interstitial pneumonia of unknown cause, occurring primarily in older adults, limited to the lungs, with the histologic and/or radiographic pattern of usual interstitial pneumonia (UIP).
Epidemiology
Incidence ~10 per 100,000; rises sharply with age (most diagnoses >60). Male predominance. Median survival from diagnosis 3-5 years without antifibrotic therapy, though highly variable.
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Sarcoidosis stage IV — Upper-lobe fibrosis, history of granulomatous disease
Combined pulmonary fibrosis and emphysema (CPFE) — Heavy smokers with upper-lobe emphysema and basal fibrosis; preserved volumes but reduced DLCO and severe PH
Diagnostic workup
Diagnostic criteria
ATS/ERS/JRS/ALAT 2018: (1) exclusion of other known causes of ILD AND (2) presence of UIP pattern on HRCT in appropriate clinical context OR (3) specific combinations of HRCT and histopathologic patterns in patients undergoing biopsy — synthesized by MDD.
Hypersensitivity pneumonitis panel (precipitins) if exposure history
BMP, CBC, LFTs (baseline for antifibrotic therapy)
Imaging
HRCT chest is central to diagnosis — UIP pattern: subpleural, basal-predominant reticulation + honeycombing ± traction bronchiectasis, with absence of inconsistent features (extensive GGO, mosaic attenuation, micronodules, consolidation, perilymphatic distribution)
Probable UIP, indeterminate UIP, and alternative diagnosis patterns help guide biopsy decision
PFTs: restrictive pattern (reduced TLC, FVC) with reduced DLCO; preserved FEV1/FVC ratio (often elevated)
6-minute walk test with desaturation (prognostic)
Echocardiogram for pulmonary hypertension
Other studies
Multidisciplinary discussion (MDD) with pulmonologist, radiologist, pathologist — gold standard for diagnosis
Surgical lung biopsy (VATS) only if HRCT pattern is inconsistent with definite/probable UIP
Cryobiopsy (less invasive) — emerging alternative in experienced centers
Bronchoscopy with BAL primarily to exclude alternatives (infection, hypersensitivity)
Diagnostic algorithm
HRCT Pattern
Key Features
Definite UIP
Subpleural, basal predominance; reticulation + honeycombing ± traction bronchiectasis; absence of inconsistent features
Probable UIP
Subpleural, basal reticulation + traction bronchiectasis without honeycombing
Indeterminate
Subpleural, basal reticulation with insufficient features for UIP, no features of alternative diagnosis
Avoid systemic glucocorticoids and immunosuppressants (PANTHER-IPF showed harm from prednisone + azathioprine + N-acetylcysteine combination)
Second-line / adjunct
Lung transplantation — early referral when FVC <80% predicted or DLCO <40% predicted; only intervention proven to improve survival
Palliative care for symptom control (dyspnea, cough, fatigue) and advance care planning
Acute exacerbations (rapid worsening dyspnea, new GGO superimposed on UIP, no infection): high-dose corticosteroids commonly used but evidence is weak; mortality >50%
Management of pulmonary hypertension associated with IPF: PAH-targeted vasodilators generally not effective; inhaled treprostinil approved for PH-ILD per INCREASE
Complications
Acute exacerbations of IPF (rapid decline, high mortality)
Pulmonary hypertension, cor pulmonale
Lung cancer (4-5× increased risk)
Pulmonary infections (bacterial, viral)
Pneumothorax
Anxiety, depression, refractory dyspnea, cough
PANCE pearls
PANTHER-IPF demonstrated HARM from prednisone + azathioprine + N-acetylcysteine combination — IPF is no longer treated with immunosuppression.
Antifibrotics (pirfenidone, nintedanib) slow but do not reverse FVC decline — start early and continue indefinitely.
Multidisciplinary discussion (pulm + radiology + pathology) is the diagnostic gold standard — avoids unnecessary biopsy.
Definite UIP on HRCT in an appropriate clinical context obviates the need for surgical lung biopsy.
Refer for lung transplant evaluation early (FVC <80% or DLCO <40%) — IPF is the second most common indication for lung transplant in the US.
References
ATS/ERS 2022 — Idiopathic Pulmonary Fibrosis (an Update) and Progressive Pulmonary Fibrosis in Adults: An Official Clinical Practice Guideline (Raghu et al., Am J Respir Crit Care Med 2022)
ASCEND — A Phase 3 Trial of Pirfenidone in Patients with Idiopathic Pulmonary Fibrosis (King et al., NEJM 2014)
INPULSIS — Efficacy and Safety of Nintedanib in Idiopathic Pulmonary Fibrosis (Richeldi et al., NEJM 2014)
PANTHER-IPF — Prednisone, Azathioprine, and N-Acetylcysteine for Pulmonary Fibrosis (Raghu et al., NEJM 2012)
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