Chemical Pneumonitis Classification and Management

Classification and Severity

The American Thoracic Society suggests that chemical pneumonitis can be classified into grades 1 to 5, with the diffuse alveolar damage (DAD) pattern being the most severe, followed by the organized pneumonia (OP) pattern, while the non-specific interstitial pneumonia (NSIP) and hypersensitivity (HP) patterns present lower grades of severity 1
Grade 2 chemical pneumonitis is characterized by symptomatic patients with mild to moderate symptoms that limit daily activities, requiring discontinuation of the causative agent and initiation of oral corticosteroids, as recommended by the Society for Immunotherapy of Cancer 2
Grade 3 chemical pneumonitis presents with severe symptoms that limit self-care, requiring hospitalization, permanent discontinuation of the causative agent, and high-dose intravenous corticosteroids, according to the European Society for Medical Oncology 3
Grade 4 chemical pneumonitis is characterized by potentially life-threatening respiratory compromise that requires urgent intervention, including mechanical ventilation, as stated by the Society for Immunotherapy of Cancer 2
Grade 5 chemical pneumonitis is fatal, representing approximately 9% of cases of pneumonitis related to immune checkpoint inhibitors, as reported by the American College of Chest Physicians 1, 2

The diffuse alveolar damage (DAD) pattern is associated with the highest grades of pneumonitis, observed as diffuse ground-glass opacity on CT images, according to the American College of Chest Physicians 1, 4
The organized pneumonia (OP) pattern is the second most severe category, being the most common pattern (23% of cases), as reported by the American College of Chest Physicians 1, 4
The non-specific interstitial pneumonia (NSIP) pattern is associated with lower grades of pneumonitis, as stated by the American College of Chest Physicians 1
The hypersensitivity (HP) pattern presents the lowest grades of severity (16% of cases) and is characterized by areas of ground-glass opacity, small nodules, and lobular areas of mosaic attenuation, according to the American College of Chest Physicians 4

Grades 2-3 chemical pneumonitis represent 66% of cases and manifest with cough, dyspnea, fatigue with daily activities, and possible requirement for supplemental oxygen, as reported by the Society for Immunotherapy of Cancer 2
Grade 4 chemical pneumonitis (9% of cases) presents with severe respiratory failure that requires mechanical ventilation, as stated by the American College of Chest Physicians and the Society for Immunotherapy of Cancer 1, 2

The American Thoracic Society recommends computed tomography (CT) scan of the chest as the preferred imaging modality to identify ground-glass opacities, nodular patchy infiltrates, or characteristic interstitial patterns of chemical pneumonitis 5
Bronchoscopy with bronchoalveolar lavage (BAL) should be performed to exclude infections, especially in grade 2 or higher pneumonitis 5
It is essential to rule out other causes of respiratory symptoms such as infectious pneumonia, tumor progression, pulmonary embolism, cardiac events, and pleural carcinomatosis 6

Hospitalize the patient immediately 7, 5
Permanently discontinue the causal agent 5
Administer high-dose intravenous corticosteroids (methylprednisolone 2-4 mg/kg/day or equivalent) 5
Consider additional immunosuppressive strategies such as infliximab, mycophenolate mofetil, or cyclophosphamide if no improvement after 48 hours 5
Provide respiratory support as needed, including supplemental oxygen and non-invasive or invasive mechanical ventilation 7

Clinical improvement after cessation of exposure to the causal agent without glucocorticoid therapy strongly supports the diagnosis of chemical-related pneumonitis 5
A clinical review should be performed for all patients approximately 6 weeks after diagnosis, either with their general physician or in a hospital clinic 8
A chest radiograph should be scheduled at that time for patients with persistent symptoms or physical signs 8

Delayed diagnosis of chemical pneumonitis is associated with greater severity of lung injury and lower reversibility, resulting in residual lung damage (fibrosis) 7
Early diagnosis and cessation of exposure to the causal agent promote optimal outcomes in patients with chemical pneumonitis 7
Patients with pre-existing lung disease are at higher risk of developing chemical pneumonitis and have poorer outcomes 7