Clinically diagnosed pneumocystis pneumonia with chronic inflammatory demyelinating polyradiculoneuropathy receiving rituximab

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is treated with corticosteroids and immunosuppressive drugs such as rituximab, which is associated with an increased risk of opportunistic infections, including Pneumocystis pneumonia (PCP), particularly in nonhuman immunodeficiency virus (HIV) immunocompromised patients. We present a 62-year-old man with CIDP on rituximab maintenance and low-dose prednisone who presented with fever, dyspnea, and hypoxia. Notable laboratories included profound lymphopenia and elevated lactate dehydrogenase. Prior bronchoalveolar lavage (BAL) showed foamy macrophages, but all direct microbiological tests for Pneumocystis jirovecii , beta-D-glucan, and viral screen were negative. Chest computed tomography showed diffuse bilateral ground-glass opacities. Based on the constellation of risk factors, clinical presentation, and imaging, the patient met the EORTC/MSGERC 2021 criteria for possible PCP. Empiric treatment with intravenous trimethoprim–sulfamethoxazole (TMP-SMX) and corticosteroids led to rapid clinical and radiographic improvement. PCP should be considered in non-HIV immunocompromised patients receiving rituximab, even with negative beta-D-glucan and BAL microscopy. The rapid clinical response to TMP-SMX strongly supports the diagnosis.