A “crazy paving” pattern on CT scan in a patient treated with Pembrolizumab.

BACKGROUND: Programmed cell death protein 1 (PD-1) and its ligand, PD-L1, have shown great promise in clinical practice and have been incorporated into standard management of NSCLC. Pneumonitis is a serious autoimmune toxicity associated with the use of anti-PD-1/PD-L1 antibodies, resulting in significant morbidity and mortality. METHODS: We described the case of a 73-year-old woman with no history of smoking developing exertional dyspnea four months after taking Pembrolizumab. RESULTS: High resolution contrast CT scan (HRCT) presented a unilateral "crazy paving" pattern, and bronchoalveolar lavage (BAL) an important lymphocytosis (20% of total cell count). The patient reached clinical stability after the administration of systemic steroids (2mg\Kg\die) and was discharged with long term oxygen therapy. DISCUSSION: Pulmonary toxicity is frequent when using PD-1 inhibitors, resulting in significant morbidity and mortality, often leading to the discontinuation of therapy. Clinical presentation is usually protean and HRCT pattern is nonspecific. This is the first case presenting a "crazy paving" pattern associated with BAL lymphocytosis. CONCLUSION: Oncologists, pulmonologists, radiologists and general practitioners have to consider PD-1 and PD-L1 inhibitor pneumonitis as a potentially disabling and fatal event.