Pulmonary Alveolar Proteinosis During Intensive Immunosuppressive Treatment for Acute Exacerbation of Interstitial Pneumonia: A Case Report and Literature Review

Pulmonary alveolar proteinosis (PAP) is a rare disease characterized by the accumulation of surfactants in the alveoli. It has been suggested that immunosuppressants contribute to the development and exacerbation of PAP. Here, we report the case of a 73-year-old man who developed secondary PAP after intensive immunosuppressive treatment for acute exacerbation of interstitial pneumonia (IP). In this case, despite the improvement of the inflammatory response after immunosuppressive treatment, Krebs von den Lungen-6 (KL-6) continued to increase, leading to the diagnosis of PAP. De-escalation of immunosuppressive treatment improved the PAP, allowing him to be discharged from the hospital. Although KL-6 is a useful marker of IP, when IP appears to be refractory and KL-6 increases despite the improvement of other inflammatory markers, physicians should consider the development of PAP and perform proactive bronchoscopic evaluation.