Can Interstitial Lung Disease (ILD) cause ground glass opacity?

Interstitial Lung Disease and Ground Glass Opacity

Yes, interstitial lung disease (ILD) commonly causes ground glass opacity (GGO) on imaging, particularly on high-resolution computed tomography (HRCT). 1

Radiological Patterns in ILD

Ground glass opacity is a characteristic radiological finding in various forms of ILD, representing areas of hazy increased lung attenuation with preservation of bronchial and vascular margins. This pattern occurs due to several pathophysiological processes:

• Non-specific Interstitial Pneumonia (NSIP): The most common HRCT abnormality in NSIP is bilateral ground glass opacity, occurring in approximately 75% of cases 1
• Connective Tissue Disease-related ILD (CTD-ILD): Ground glass opacities with or without reticulations are commonly seen, particularly in non-specific interstitial pneumonia pattern 1
• Hypersensitivity Pneumonitis: Shows patchy ground glass opacities, often with upper lung predominance 1
• Smoking-related ILDs: Respiratory bronchiolitis-ILD presents with ground glass opacity and centrilobular nodules 1

Pathophysiological Basis of GGO in ILD

Ground glass opacities in ILD represent:

• Partial filling of air spaces
• Inflammatory or fibrotic interstitial thickening
• Increased capillary blood volume
• Early stages of fibrotic changes 2

Clinical Significance of GGO in ILD

The presence of ground glass opacities in ILD has important clinical implications:

1. Potential Treatability: GGO may represent active and potentially treatable disease, particularly in idiopathic pulmonary fibrosis and other interstitial lung diseases 3

2. Disease Activity: In many forms of ILD, GGO often indicates active inflammation that may be responsive to immunosuppressive therapy 4

3. Prognostic Value: The American Thoracic Society and European Respiratory Society suggest that GGOs may indicate early, potentially reversible disease 3

4. Treatment Response Indicator: Serial imaging showing changes in GGO extent can help monitor disease progression or response to therapy 3

Differential Diagnosis of GGO

While ILD is a common cause of GGO, other conditions should be considered:

• Pulmonary edema
• Pneumocystis pneumonia
• Alveolar proteinosis
• Drug-induced lung disease
• Radiation pneumonitis
• Viral pneumonias (including COVID-19) 5, 6

Management Implications

The detection of ground glass opacities in ILD guides management decisions:

• Antifibrotic therapy: Nintedanib or pirfenidone for idiopathic pulmonary fibrosis 4
• Immunomodulatory therapy: Mycophenolate mofetil for CTD-ILD, which may slow decline or improve forced vital capacity 4
• Monitoring: Serial HRCT is important to assess disease progression or treatment response 3

Pitfalls and Caveats

1. Physiological GGO: Poor ventilation of dependent lung areas and expiratory effects can mimic pathological GGO 6

2. Expiratory Scans: Essential to differentiate GGO caused by infiltrative processes from mosaic patterns due to vascular diseases or airway abnormalities 2, 7

3. Medication-Related Complications: Some medications used to treat ILD, like cyclophosphamide and mycophenolate mofetil, can themselves cause interstitial lung disorders and pulmonary fibrosis 8, 9

4. Coexisting Patterns: Multiple pathologic and/or HRCT patterns may be found in the same patient, requiring careful multidisciplinary discussion to determine clinical significance 1

In conclusion, ground glass opacity is a common and significant finding in interstitial lung disease, often indicating active inflammation and potential treatability. HRCT remains the gold standard for evaluation of ILD and proper characterization of GGO patterns.