Checkpoint inhibitor pneumonitis (CIP) is a rare but potentially devastating complication of immune checkpoint inhibitor therapy. Due to its nonspecific and variable clinical appearance, CIP can be misdiagnosed or recognized late, resulting in delayed treatment and poor clinical outcomes. We report the case of a 65-year-old female patient with chronic obstructive pulmonary disease (COPD), a significant smoking history, and non-small cell lung carcinoma (NSCLC) who had an atypical early, moderate-to-severe CIP after just two infusions of pembrolizumab. During hospitalization, she demonstrated minimal improvement on empiric treatment for COPD, congestive heart failure (CHF) exacerbation, and pneumonia. On day 9 of hospitalization, computed tomography identified ground-glass opacities in the right posterior lung, prompting escalation of steroid treatment to 2 mg/kg/day to treat CIP. The patient subsequently improved, returned to her baseline oxygen requirements, and was discharged with plans to discontinue pembrolizumab therapy. This case report highlights the atypically early and rapid development of pembrolizumab-induced CIP, demonstrating the need for timely diagnosis and medical intervention. It also raises important questions regarding the continuation of immunotherapy following CIP.
