Differential Diagnosis for Reticulonodular Opacities on CT Chest

Idiopathic Interstitial Pneumonias

• The American Thoracic Society recommends that patchy, predominantly peripheral, subpleural, bibasal reticular abnormalities with limited ground glass opacity are characteristic of Idiopathic Pulmonary Fibrosis (IPF) 1, 2
• Traction bronchiectasis, bronchiolectasis, and subpleural honeycombing develop in areas of severe IPF involvement 1
• When ground glass opacity exceeds 30% of lung involvement, consider alternative diagnoses rather than IPF, according to the American Journal of Respiratory and Critical Care Medicine 1, 3
• HRCT diagnosis by experienced observers achieves approximately 90% accuracy for UIP pattern, as stated by the American Journal of Respiratory and Critical Care Medicine 1
• Nonspecific Interstitial Pneumonia (NSIP) is characterized by bilateral symmetric ground glass opacities or bilateral air space consolidation with a temporally uniform appearance, according to the American Journal of Respiratory and Critical Care Medicine 4
• Reticular opacities are present but honeycombing is rare in NSIP, as noted by the American Journal of Respiratory and Critical Care Medicine 4
• NSIP has a better prognosis than IPF with 15-20% mortality at 5 years and most patients improve with corticosteroids, according to the American Journal of Respiratory and Critical Care Medicine 4
• Desquamative Interstitial Pneumonitis (DIP) is characterized by extensive ground glass opacities (>30% lung involvement), as stated by the American Journal of Respiratory and Critical Care Medicine 1, 3
• DIP occurs in current or former cigarette smokers, according to the American Journal of Respiratory and Critical Care Medicine 4
• DIP has a better prognosis than IPF with approximately 70% survival at 10 years, as noted by the American Journal of Respiratory and Critical Care Medicine 4
• Respiratory Bronchiolitis-Interstitial Lung Disease (RBILD) is characterized by diffuse fine reticular or nodular interstitial opacities with hazy opacities on HRCT, according to the American Journal of Respiratory and Critical Care Medicine 4, 3
• Centrilobular nodules are often present in RBILD, as stated by Praxis Medical Insights: Practical Summaries of Clinical Guidelines 3
• RBILD is associated with current or former cigarette smoking, according to the American Journal of Respiratory and Critical Care Medicine 4

Connective Tissue Disease-Related ILD

• Scleroderma and rheumatoid arthritis commonly produce CT appearances similar to IPF, as noted by the American Journal of Respiratory and Critical Care Medicine 1
• High titers of anti-nuclear antibodies (>1:160) or rheumatoid factor suggest underlying connective tissue disease, according to the American Journal of Respiratory and Critical Care Medicine 2, 5
• Bilateral basal reticular pattern is characteristic of connective tissue disease, as stated by the American Journal of Respiratory and Critical Care Medicine 2, 5

Occupational and Environmental Exposures

• Asbestosis has a CT appearance similar to IPF but is distinguished by parenchymal bands of fibrosis and pleural plaques, according to the American Journal of Respiratory and Critical Care Medicine 1
• Bilateral basal reticular pattern is present in asbestosis, as noted by the American Journal of Respiratory and Critical Care Medicine 2
• Hypersensitivity pneumonitis (HP) is characterized by reticular opacity or honeycombing often lacking the bibasilar predominance seen in IPF, according to the American Journal of Respiratory and Critical Care Medicine 1
• Centrilobular nodules, middle and upper lobe predominance, and absence of honeycombing favor HP over IPF, as stated by the American Journal of Respiratory and Critical Care Medicine 1
• Ground glass opacities without basal or peripheral predominance are present in HP, according to the American Journal of Respiratory and Critical Care Medicine 1, 3

Drug-Related Pneumonitis

• Temporal relationship between drug exposure and onset of disease is critical for diagnosis, as noted by Chest 6, 7
• Multiple patterns are possible, including NSIP, organizing pneumonia (OP), diffuse alveolar damage (DAD), HP pattern, and pulmonary eosinophilia, according to Chest 6, 7, 8
• Common culprits include molecular targeting agents (EGFR-TKIs, mTOR inhibitors) and immune checkpoint inhibitors, as stated by Chest 6, 8
• Improvement with drug cessation supports diagnosis, according to Chest 6, 7

Critical Diagnostic Approach

• Peripheral and basal predominance is characteristic of IPF, asbestosis, and connective tissue disease, as noted by the American Journal of Respiratory and Critical Care Medicine 1, 2
• Upper and mid-lung predominance is characteristic of hypersensitivity pneumonitis and sarcoidosis, according to the American Journal of Respiratory and Critical Care Medicine 1
• Diffuse bilateral symmetric pattern is characteristic of NSIP and drug-related pneumonitis, as stated by the American Journal of Respiratory and Critical Care Medicine 4, 8
• Honeycombing is common in IPF and rare in NSIP, according to the American Journal of Respiratory and Critical Care Medicine 1, 4
• Traction bronchiectasis with ground glass always indicates fibrosis, as noted by the American Journal of Respiratory and Critical Care Medicine 1, 3
• Centrilobular nodules are characteristic of hypersensitivity pneumonitis and RBILD, according to the American Journal of Respiratory and Critical Care Medicine 1, 3
• Pleural plaques are characteristic of asbestosis, as stated by the American Journal of Respiratory and Critical Care Medicine 1
• Lymphadenopathy is characteristic of sarcoidosis, tuberculosis, and malignancy, according to the American Journal of Respiratory and Critical Care Medicine 1

Clinical Context Integration

• Smoking history is associated with DIP and RBILD, as noted by the American Journal of Respiratory and Critical Care Medicine 4
• Occupational exposures are associated with asbestosis and hypersensitivity pneumonitis, according to the American Journal of Respiratory and Critical Care Medicine 1
• Medication history is critical for diagnosing drug-related pneumonitis, as stated by Chest 6, 7, 8
• Systemic symptoms are associated with connective tissue disease and infection, according to the American Journal of Respiratory and Critical Care Medicine 2
• Prior malignancy is associated with metastatic disease and lymphangitic spread, as noted by Chest 6