Case Report: Sintilimab-associated acute interstitial nephritis in a patient with severe thrombocytopenia: clinical diagnosis and treatment strategy when renal biopsy is contraindicated.

Background: Immune checkpoint inhibitors (ICIs) have become one of the core drugs for the comprehensive treatment of advanced gastric cancer. As a representative domestic PD-1 inhibitor, sintilimab has shown significant efficacy in clinical application, but the management of immune-related adverse events (irAEs) remains a clinical challenge. Among them, the incidence of immune-related acute kidney injury (ir-AKI) is only 16.5%-17%, but it is mainly manifested as acute interstitial nephritis (AIN), which can progress to irreversible renal failure in severe cases. In particular, when ICIs are combined with potentially nephrotoxic chemotherapeutic drugs (e.g., oxaliplatin), the difficulty of etiological identification increases. Renal biopsy, the gold standard for diagnosis, cannot be performed in the presence of contraindications such as severe thrombocytopenia, further exacerbating the dilemma of diagnosis and treatment. Case Summary: This paper reports a 68-year-old male patient with gastric antrum adenocarcinoma (cT4aN2M0, stage III) who developed progressive elevation of serum creatinine (from a baseline of 89 μmol/L to 663 μmol/L) accompanied by scattered erythematous papules all over the body, severe thrombocytopenia (minimum 24 × 10 Conclusion: Sintilimab-associated AIN can present with the coexistence of multisystem irAEs. In the presence of contraindications to renal biopsy, comprehensive assessment based on medication timeline, clinical phenotype, laboratory indicators and treatment response is the core of diagnosis. Early initiation of individualized glucocorticoid therapy can effectively reverse renal function injury, and multidisciplinary team (MDT) collaboration is the key to optimizing the management of complex irAEs. This case provides a feasible diagnosis and treatment pathway for similar clinical dilemmas.