What are the diagnostic criteria for Idiopathic Pulmonary Arterial Fibrosis (IPAF)?

IPAF Diagnostic Criteria

The term "IPAF" (Interstitial Pneumonia with Autoimmune Features) is not addressed in the provided evidence, which focuses exclusively on IPF (Idiopathic Pulmonary Fibrosis). The question appears to contain a terminology error—"Idiopathic Pulmonary Arterial Fibrosis" does not exist as a clinical entity. I will clarify the correct diagnostic criteria for IPF based on the most recent guidelines.

Diagnostic Criteria for Idiopathic Pulmonary Fibrosis (IPF)

The 2018 ATS/ERS/JRS/ALAT guidelines establish that IPF diagnosis requires exclusion of other known causes of interstitial lung disease (ILD) plus either a UIP pattern on high-resolution CT (HRCT) or specific combinations of HRCT and histopathology patterns in patients who undergo lung biopsy. 1, 2

Essential Exclusion Criteria

Before diagnosing IPF, you must systematically exclude:

• Environmental exposures (home, work, and other frequent locations) including hypersensitivity pneumonitis triggers 1, 2
• Drug toxicity (amiodarone, methotrexate, nitrofurantoin, and other fibrogenic medications) 1, 2, 3
• Connective tissue diseases through serological testing (ANA, rheumatoid factor, anti-CCP) 1, 2
• Familial forms in patients <50 years or with family history (consider telomerase complex genes and surfactant protein-C genes) 1

HRCT Pattern Classification (2018 Update)

The 2018 guidelines refined the previous categories into four distinct patterns 1:

1. UIP Pattern (Diagnostic for IPF)

• Subpleural and basal predominance 1, 2, 4
• Reticular abnormalities with honeycombing (clustered cystic airspaces 3-10mm with thick walls) 1, 2
• Traction bronchiectasis with or without honeycombing 1, 4
• Absence of features inconsistent with UIP 1, 2

If HRCT shows definite UIP pattern in appropriate clinical context, IPF can be diagnosed without surgical lung biopsy. 1, 4

2. Probable UIP Pattern

• Reticular abnormalities with peripheral and basal predominance 1
• Absence of honeycombing 1, 3
• May have traction bronchiectasis 1

3. Indeterminate for UIP Pattern

• Subtle reticulation without other defining features 1
• Requires additional diagnostic evaluation 1

4. Alternative Diagnosis Pattern

• Features inconsistent with UIP (extensive ground-glass opacity >30%, nodules, pleural effusion, lymphadenopathy) 1, 3

Diagnostic Algorithm for Non-UIP HRCT Patterns

For patients with probable UIP, indeterminate for UIP, or alternative diagnosis patterns on HRCT, the 2018 guidelines conditionally recommend: 1

• Bronchoalveolar lavage (BAL) to exclude alternative diagnoses (lymphocytosis >30% suggests hypersensitivity pneumonitis or NSIP, not IPF) 1
• Surgical lung biopsy (SLB) via video-assisted thoracoscopic surgery after multidisciplinary discussion and risk assessment 1

For patients with definite UIP pattern on HRCT, the guidelines strongly recommend AGAINST performing SLB, transbronchial biopsy, or cryobiopsy. 1

Clinical Context Requirements

IPF typically presents with 4, 5:

• Age >60 years (though younger patients with familial forms exist) 1, 4
• Male predominance 4
• Insidious onset of progressive exertional dyspnea 4, 5
• Nonproductive cough 4, 5
• Fine bibasilar inspiratory crackles (dry or "Velcro"-type) on examination 1, 4
• History of cigarette smoking in majority 4

Pulmonary Function Testing

Obtain forced vital capacity (FVC) and diffusing capacity of the lung for carbon monoxide (DLCO) in all suspected IPF patients. 1 Typical findings include:

• Restrictive pattern (reduced FVC and total lung capacity) 1
• Early decrease in DLCO 1
• Hypoxemia at rest or with exercise 1, 5

Multidisciplinary Discussion

The 2018 guidelines conditionally recommend multidisciplinary discussion involving pulmonologists, radiologists, and pathologists with ILD expertise for all cases where diagnosis is uncertain. 1, 6, 5

Critical Pitfalls to Avoid

• Do not diagnose IPF without systematically excluding hypersensitivity pneumonitis—this is the most common misdiagnosis 3
• Do not rely on chest radiograph alone—HRCT is mandatory 3
• Do not dismiss reticular opacities as "just atelectasis" without confirming absence of traction bronchiectasis or honeycombing 3
• Do not assume honeycombing is required for IPF diagnosis—the 2018 "probable UIP" category allows diagnosis without honeycombing when combined with appropriate biopsy findings 1, 3
• HRCT misdiagnosis by less experienced radiologists is a major problem—seek expert radiology review when available 7

Note on IPAF

If the question intended to ask about IPAF (Interstitial Pneumonia with Autoimmune Features), this is a separate entity proposed in 2015 for patients with ILD who have autoimmune features but do not meet criteria for definite connective tissue disease. This classification is not covered in the provided evidence, which focuses exclusively on IPF.