What is the diagnostic approach for acute interstitial pneumonia (AIP)?

From the Guidelines

The diagnostic approach for acute interstitial pneumonia (AIP) should involve a combination of clinical evaluation, imaging, and often lung biopsy, prioritizing high-resolution computed tomography (HRCT) and surgical lung biopsy for definitive diagnosis, as outlined in the most recent guidelines 1. The initial assessment should include a thorough history focusing on symptom onset, physical examination, and laboratory tests including complete blood count, comprehensive metabolic panel, and arterial blood gases to assess oxygenation.

• Key features of AIP include:
  • Rapidly progressive hypoxemia
  • Mortality of 50% or more
  • No proven treatment
  • Survivors usually have a good long-term prognosis
• HRCT is essential and typically shows:
  • Bilateral patchy ground-glass opacities
  • Consolidation of the dependent lung
  • Distortion of bronchovascular bundles and traction bronchiectasis in the later stages
• Bronchoalveolar lavage (BAL) should be performed to exclude infection and malignancy, with findings often showing neutrophilia.
• Surgical lung biopsy via video-assisted thoracoscopic surgery is frequently necessary for definitive diagnosis, revealing diffuse alveolar damage with hyaline membranes, similar to ARDS but without an identifiable cause 1. It's crucial to rule out other causes of acute respiratory failure including infections, drug toxicity, connective tissue diseases, and other interstitial lung diseases.
• Pulmonary function tests, if the patient can perform them, typically show a restrictive pattern with reduced diffusion capacity. Early diagnosis is critical as AIP has high mortality (>50%) and requires prompt management with supportive care, mechanical ventilation, and consideration of corticosteroids and immunosuppressants, as supported by the American Thoracic Society and European Respiratory Society statement 1.

From the Research

Diagnostic Approach for Acute Interstitial Pneumonia (AIP)

The diagnostic approach for AIP involves a combination of clinical evaluation, imaging studies, and histological examination.

• Clinical presentation: AIP is characterized by progressive hypoxic respiratory failure, high mortality rate, and absence of guidelines for its treatment 2.
• Imaging studies:
  • Chest radiograph: shows diffuse bilateral reticulonodular opacities 2.
  • Computed tomography (CT): reveals diffuse ground-glass opacities 2, 3.
  • High-resolution computed tomography (HRCT): shows areas of ground glass attenuation and alveolar consolidation 3.
• Histological examination:
  • Biopsy: shows diffuse alveolar damage (DAD) pattern, with organizing diffuse alveolar damage 2, 3, 4.
  • Bronchoalveolar lavage (BAL): findings are characteristic, with a huge neutrophilia associated with scattered atypical type II pneumocytes collected in clusters with extracellular amorphous material (fragments of hyaline membranes) 3.

Diagnostic Criteria

The diagnosis of AIP is established after extensive work-up that excludes the known risk factors for acute respiratory distress syndrome 2.

• The use of an aggressive diagnostic approach, including early BAL and surgical lung biopsy, can help establish the diagnosis of AIP 5.

Timing of Diagnostic Procedures

• Early diagnostic procedures, such as BAL and surgical lung biopsy, can be performed within a few days of hospital admission 5.
• The early institution of immunosuppressive therapy, such as high-dose steroid pulse therapy, may improve clinical outcome in patients with AIP 5.