What is the differential diagnosis and recommended work‑up for an asymmetric right hemidiaphragm with basilar linear atactic bands on imaging?

Differential Diagnosis and Work-Up for Asymmetric Right Hemidiaphragm with Basilar Linear Atelectatic Bands

The most likely diagnosis is asbestos-related pleural disease with associated parenchymal bands, and the initial work-up should include detailed occupational/environmental exposure history followed by high-resolution CT chest to characterize pleural plaques and parenchymal fibrosis. 1, 2

Primary Differential Diagnoses

Asbestos-Related Disease (Most Likely)

• Pleural plaques on the diaphragm appear as linear calcifications seen on edge on the right hemidiaphragm and are almost invariably associated with asbestos exposure when multiple lesions are present. 1
• Parenchymal bands of fibrosis are characteristic of asbestosis and help distinguish it from idiopathic pulmonary fibrosis, typically presenting with a bilateral basal reticular pattern. 1, 2
• The presence of pleural plaques indicates elevated risk of mesothelioma and lung cancer beyond what occupational history alone might suggest, serving as a marker for greater retained body burden. 1
• Even without radiographic interstitial fibrosis, pleural plaques can cause restrictive impairment with approximately 5% reduction in FVC. 1

Diaphragmatic Dysfunction

• An elevated or asymmetric hemidiaphragm may indicate paralysis, weakness, or eventration, all of which require functional imaging for definitive diagnosis. 3, 4
• Diaphragmatic paralysis shows absence of orthograde excursion with paradoxical motion on sniffing during fluoroscopy. 3
• Diaphragmatic weakness demonstrates reduced or delayed orthograde excursion on deep breathing. 3
• Static chest radiography alone cannot reliably distinguish between these entities and may only suggest dysfunction. 1, 3

Interstitial Lung Disease Patterns

• Basilar linear opacities with peripheral predominance suggest idiopathic pulmonary fibrosis, connective tissue disease-related ILD, or asbestosis. 2, 5
• Parenchymal bands (linear opacities extending from pleura to lung parenchyma) are particularly characteristic of asbestosis rather than IPF. 1, 2
• The presence of traction bronchiectasis with these bands indicates fibrosis. 2

Recommended Diagnostic Algorithm

Step 1: Detailed Exposure and Clinical History

• Obtain comprehensive occupational history focusing on asbestos exposure (insulation work, shipyard work, construction, sheet metal work) as systematic questioning identifies reversible or specific causes in substantial proportions of patients. 1, 5
• Document medication history to exclude drug-related pneumonitis, as temporal relationship between drug exposure and disease onset is critical. 2, 5
• Assess for connective tissue disease symptoms, as high titers of anti-nuclear antibodies (>1:160) or rheumatoid factor suggest underlying connective tissue disease. 2
• Evaluate for respiratory symptoms including dyspnea severity, orthopnea (suggesting diaphragmatic dysfunction), and presence of bibasilar inspiratory crackles. 5

Step 2: High-Resolution CT Chest (Essential Next Step)

• HRCT should be obtained immediately as conventional chest radiography misses up to 34% of interstitial lung disease cases and cannot adequately characterize pleural abnormalities. 5
• HRCT readily identifies pleural plaques with sharp, often foliate borders when seen face-on and raised straight surfaces with clear cut-off edges. 1
• Axial CT scans may fail to image diaphragmatic plaques adequately; multiplanar reconstructions improve detection. 1
• HRCT distinguishes asbestosis (peripheral/basal reticular pattern with parenchymal bands and pleural plaques) from IPF (lacks pleural plaques) and hypersensitivity pneumonitis (upper/mid-lung predominance with centrilobular nodules). 2

Step 3: Functional Assessment of Diaphragm

• Fluoroscopy is the established standard for diagnosing diaphragmatic dysfunction, providing simple and effective functional assessment. 1, 3
• Fluoroscopy should evaluate quiet breathing, deep breathing, and sniff maneuvers to differentiate paralysis from weakness. 3
• Ultrasound is concordant with fluoroscopic findings and offers advantages as a bedside technique without radiation, measuring diaphragmatic excursion amplitude, thickness, and contraction. 1, 6
• Dynamic MRI with cine sequences allows comprehensive analysis of diaphragm and chest wall muscle movement but is not typically indicated for initial imaging. 1

Step 4: Additional Testing Based on HRCT Findings

If Pleural Plaques Confirmed:

• No surgical lung biopsy is needed if classic pleural plaques are identified with appropriate exposure history. 1
• Pulmonary function testing should be performed to assess restrictive impairment and diffusing capacity, as plaques alone can reduce FVC by approximately 5%. 1
• Long-term surveillance for mesothelioma and lung cancer is warranted given elevated risk. 1

If Interstitial Pattern Without Plaques:

• Determine if HRCT shows definite UIP pattern (peripheral/basal reticular abnormalities, traction bronchiectasis, honeycombing), which allows confident IPF diagnosis without biopsy when other causes are excluded. 5
• Probable UIP or indeterminate patterns require multidisciplinary discussion and often surgical lung biopsy. 5
• Serologic testing for connective tissue disease should be obtained if bilateral basal reticular pattern is present. 2

If Diaphragmatic Dysfunction Confirmed:

• Evaluate for underlying causes including prior surgery, trauma, tumor, infection, or neurologic disease. 3, 4
• Symptomatic patients with confirmed paralysis or eventration should be considered for diaphragm plication. 4

Critical Pitfalls to Avoid

• Do not rely on chest radiography alone, as it has unacceptably low sensitivity for early ILD and may appear normal in significant disease. 5
• Do not mistake subpleural fat pads (which have gradually tapering edges) for pleural plaques (which have sharp, cut-off edges). 1
• Do not confuse atelectatic streaks or visceral folds with diaphragmatic plaques; calcification helps distinguish true plaques. 1
• Do not perform surgical lung biopsy if HRCT shows definite UIP pattern with pleural plaques and appropriate exposure history, as this confidently indicates asbestosis. 1, 5
• Do not overlook the need for proper radiographic penetration, as underpenetrated films may miss calcification in pleural plaques. 1