What is the diagnostic workup for Acute Interstitial Pneumonia (AIP)?

From the Guidelines

The diagnostic workup for acute interstitial pneumonia (AIP) should include a comprehensive approach combining clinical assessment, imaging, and often lung biopsy, with a focus on rapid diagnosis to initiate appropriate treatment due to its high mortality rate. The initial evaluation should include a thorough history and physical examination, focusing on rapid-onset respiratory symptoms, exclusion of identifiable causes, and assessment of hypoxemia. Laboratory tests should include complete blood count, comprehensive metabolic panel, inflammatory markers (CRP, ESR), and blood cultures to rule out infection, as suggested by the American Thoracic Society 1. Arterial blood gas analysis is essential to evaluate gas exchange and acid-base status.

High-resolution computed tomography (HRCT) is the imaging modality of choice, typically showing bilateral ground-glass opacities and consolidation with a predominantly basal and peripheral distribution, as described in the 2013 American Thoracic Society/European Respiratory Society statement 1. Pulmonary function tests often demonstrate a restrictive pattern with reduced diffusion capacity. Bronchoscopy with bronchoalveolar lavage (BAL) should be performed to exclude infection and malignancy, with fluid sent for cell count, culture, cytology, and special stains, as recommended by the 2012 American Thoracic Society clinical practice guideline 1.

Surgical lung biopsy via video-assisted thoracoscopic surgery (VATS) is frequently necessary for definitive diagnosis, showing diffuse alveolar damage with hyaline membrane formation, as noted in the 2000 American Thoracic Society international consensus statement 1. The biopsy should be performed from multiple lobes to account for heterogeneity. Echocardiography may be indicated to exclude cardiac causes of respiratory failure. Key considerations in the diagnostic workup include:

• Rapid onset of symptoms
• Exclusion of identifiable causes
• Assessment of hypoxemia
• Imaging with HRCT
• Laboratory tests to rule out infection
• BAL to exclude infection and malignancy
• Surgical lung biopsy for definitive diagnosis
• Echocardiography to exclude cardiac causes of respiratory failure.

Given the high mortality rate of AIP, a comprehensive and rapid diagnostic workup is crucial to initiate appropriate treatment, as emphasized by the 2013 American Thoracic Society/European Respiratory Society statement 1.

From the Research

Diagnostic Workup for Acute Interstitial Pneumonia (AIP)

The diagnostic workup for AIP involves a combination of clinical evaluation, imaging studies, and histological examination. The key features of AIP include:

• Progressive hypoxic respiratory failure
• High mortality rate
• Absence of guidelines for treatment
• Characteristic histology finding of diffuse alveolar damage (DAD) 2 Some of the diagnostic tests used to evaluate AIP include:
• Chest radiograph: shows diffuse bilateral reticulonodular opacities 2
• Computed tomography (CT): shows diffuse ground-glass opacities 2, 3
• High-resolution CT (HRCT): shows areas of ground glass attenuation and alveolar consolidation 3
• Bronchoalveolar lavage (BAL): shows a huge neutrophilia associated with scattered atypical type II pneumocytes 3
• Lung biopsy: shows histological features consistent with the organising form of diffuse alveolar damage pattern 3
• Autoantibody testing: may be positive in some cases, such as anti-SSA/Ro52 4

Imaging Features

The imaging features of AIP can be distinguished from those of other interstitial lung diseases, such as nonspecific interstitial pneumonia (NSIP) and usual interstitial pneumonia (UIP). The key imaging features of AIP include:

• Spatially uniform, bilateral, basal-predominant ground-glass and/or reticular opacities with little if any honeycombing 5
• Areas of ground glass attenuation and alveolar consolidation on HRCT 3 In contrast, UIP is characterized by a spatially inhomogeneous, bilateral, peripheral, basal-predominant pattern of reticular opacities and honeycombing with little if any ground-glass attenuation 5.

Clinical Evaluation

The clinical evaluation of AIP involves a thorough history and physical examination, as well as laboratory tests to exclude other causes of acute respiratory distress syndrome (ARDS). The key clinical features of AIP include:

• Progressive dyspnea
• Acute respiratory failure
• Absence of known risk factors for ARDS 2
• Presence of autoantibodies in some cases 4 The clinical course of AIP can be variable, with some patients experiencing recurrences and chronic, progressive interstitial lung disease 6.