What are the diagnostic criteria to differentiate pneumonitis (inflammation of the lungs)?

From the Guidelines

Pneumonitis can be diagnosed and differentiated through a combination of clinical presentation, imaging findings, laboratory tests, and sometimes lung biopsy, with the most recent and reliable evidence suggesting that CT imaging is more reliable than chest radiographs in identifying new or progressive pulmonary infiltrates and ground glass changes 1. The diagnosis of pneumonitis is a complex process that involves multiple steps and considerations.

• Patients typically present with shortness of breath, dry cough, fatigue, fever, and sometimes chest pain.
• On physical examination, crackles may be heard during lung auscultation.
• Chest imaging is crucial, with chest X-rays showing bilateral interstitial infiltrates and ground-glass opacities, while high-resolution CT scans provide more detailed visualization of ground-glass opacities, consolidation, and reticular patterns.
• Laboratory tests may reveal elevated inflammatory markers, and pulmonary function tests often show restrictive patterns with decreased diffusion capacity.
• Bronchoscopy with bronchoalveolar lavage can help identify specific causes by analyzing cellular composition and potential infectious agents. Some key points to consider in the diagnosis of pneumonitis include:
• The presence of new or progressive pulmonary infiltrates and ground glass changes on lung imaging studies, as suggested by the study published in the Journal for ImmunoTherapy of Cancer 1.
• The importance of monitoring baseline and ongoing oxygen saturation, as well as chest CT, pulmonary function tests, and a 6-min walk test, as recommended by the same study 1.
• The potential need for a pulmonology consult and infectious disease consultation, especially in cases with atypical symptoms such as fever and productive cough 1.
• The use of fiberoptic bronchoscopy with BAL to exclude competing diagnoses, and the potential role of lung biopsies in certain cases, as discussed in the study published in the Journal for ImmunoTherapy of Cancer 1. It's also important to consider the temporal relationship to potential exposures, response to removal of the offending agent, and excluding other causes like infection or heart failure, as well as the pattern of onset and clinical context, as mentioned in the example answer. Overall, the diagnosis of pneumonitis requires a comprehensive approach that takes into account multiple factors and considerations, with the goal of establishing a definitive diagnosis and guiding effective treatment.
• The most recent and highest quality study, published in the Journal for ImmunoTherapy of Cancer 1, provides the most reliable evidence for the diagnosis of pneumonitis, and should be prioritized in clinical practice.

From the Research

Diagnostic Criteria for Pneumonitis

The diagnostic criteria for pneumonitis, particularly in the context of drug-related pneumonitis (DRP) and immune checkpoint inhibitor-induced pneumonitis (ICI-pneumonitis), involve a combination of clinical evaluation, imaging features, and exclusion of other potential causes 2, 3, 4.

• The diagnosis of DRP is usually achieved by excluding other potential known causes, with awareness of the incidence and risk factors for DRP becoming increasingly important 2.
• Imaging features of DRP should be assessed in consideration of the distribution of lung parenchymal abnormalities, with CT patterns reflecting acute, subacute, and chronic interstitial disease 2.
• A single drug can be associated with multiple radiologic patterns, making diagnosis and management challenging 2.
• The evaluation of ICI-pneumonitis involves radiographically proven pneumonitis, with the diagnosis established after excluding alternative aetiologies either by a bronchoscopy or a thorough examination of clinical features 4.

Imaging Features

Imaging features play a crucial role in the diagnosis of pneumonitis, with high-resolution computed tomography (HRCT) providing important clues 5.

• The HRCT findings in hypersensitivity pneumonitis (HP) may include ground-glass opacification, centrilobular nodules, air trapping (mosaic pattern), fibrosis, emphysema, or more frequently a combination of these 5.
• The combination of a mosaic pattern with ground-glass opacification and centrilobular nodules is particularly suggestive of the diagnosis of HP 5.
• A CT-derived signature using a habitat imaging algorithm can help distinguish pneumonia and ICI-pneumonitis, with intrinsic lung inflammation patterns identified by segregating infected lungs into clusters ("habitats") 3.

Clinical Evaluation

Clinical evaluation is essential for the diagnosis of pneumonitis, with a high degree of clinical suspicion and a thorough occupational and environmental history necessary for accurate diagnosis 5, 6.

• The presence of fibrosis is associated with higher morbidity and mortality in HP, and differentiating fibrotic HP from the idiopathic interstitial pneumonias can be a challenge 6.
• Stratification of patients is important in managing ICI-pneumonitis, with factors such as ICI-pneumonitis grade, time of onset, prior lines of chemotherapy, and accompanying immune-related adverse events influencing management decisions 4.