[Immune checkpoint inhibitor-related pneumonitis : Differential diagnosis strategies]

Immune checkpoint inhibitor-related pneumonitis (ICI-P) is a potentially serious complication of cancer therapy with immune checkpoint inhibitors. The clinical presentation is nonspecific, typically involving dyspnea and cough. Differentiating the imaging patterns on computed tomography (CT) is challenging. The most important differential diagnoses include infectious pneumonia, radiation-induced changes, and tumor progression with lymphangitic carcinomatosis.

Noncontrast high-resolution thin-section CT (HRCT) is the modality of choice. Common patterns include bilateral ground-glass opacities and patterns of organizing pneumonia (OP), nonspecific interstitial pneumonia (NSIP), bronchiolocentric interstitial pneumonia (BIP), and diffuse alveolar damage (DAD). Diagnosis is based on correlation with clinical presentation, laboratory parameters, and exclusion of infectious causes, if necessary by bronchoalveolar lavage (BAL).

Pattern classifications according to the recommendations of the Fleischner Society facilitate systematic categorization of the heterogeneous CT findings. Particular attention should be paid to distinguishing these from infection and lymphangitic carcinomatosis. Assessment over time is important, as CT changes often resolve with delay, and specific courses such as chronic ICI pneumonitis or pneumonitis flares may occur.

In cases of new pulmonary changes, the typical temporal association with ICI therapy (weeks to months, on average 3 months after the first ICI dose), risk factors, and characteristic HRCT patterns should be taken into account. The changes usually regress over weeks to months upon interruption of ICI therapy and/or administration of glucocorticoids.