The high-dose methotrexate (MTX) regimen is a first-line treatment for primary central nervous system diffuse large B-cell lymphoma (PCNS-DLBCL). However, MTX-related kidney injury is a severe treatment complication. No cases of capillary leak syndrome (CLS) causing delayed MTX metabolism-associated renal failure have been reported.

A 48-year-old female presented to Zibo Central Hospital in April 2024 with headaches. Contrast-enhanced magnetic resonance imaging (MRI) of the brain revealed a space-occupying lesion in the right occipital lobe. A stereotactic biopsy was performed to determine the nature of the lesion. Postoperative pathology confirmed DLBCL. The patient underwent a TZM regimen, which included Tislelizumab, MTX, and Zanubrutinib. On the first day following MTX, the patient developed generalized edema, shortness of breath, and reduced urine output. Laboratory tests revealed hypoxemia, low albumin levels, and acute kidney injury. Based on these findings, the patient was diagnosed with CLS. To quickly lower the blood MTX concentration, pleural effusion drainage and continuous renal replacement therapy (CRRT) were performed. The treatment was successful, and the patient recovered and was discharged.

CLS is a serious complication for DLBCL patients receiving high-dose MTX therapy.