Background: Chimeric antigen receptor T-cell (CAR-T) therapy has revolutionised the treatment of relapsed/refractory diffuse large B-cell lymphoma (r/r DLBCL). Still, it can lead to severe immunosuppression and late-onset complications. We report a rare case of mucormycosis-related cavernous sinus orbital apex syndrome (CSOAS) in a patient with r/r DLBCL who developed prolonged pancytopenia after receiving anti-CD19 CAR-T therapy.

Case Presentation: A patient with r/r DLBCL received anti-CD19 CAR-T therapy and subsequently developed prolonged pancytopenia. The patient was initially treated with a combination of amphotericin B and isavuconazole, but amphotericin B was discontinued due to nephrotoxicity before reaching the target dose (30 mg/day). Surgical removal of the lesions and drainage of the sinuses was performed, and the patient continued on isavuconazole. Supportive treatments, including granulocyte colony-stimulating factor and eltrombopag, were administered.

Results: After surgery, the patient's fever and facial oedema resolved, and their vision improved. Blood cell counts normalised (white blood cell 4–11 × 10⁹/L) 1 week later.

Conclusion: This case represents one of the first reports of mucormycosis-associated CSOAS following CAR-T therapy successfully managed despite challenges with antifungal treatment. It underscores the importance of dynamic infection surveillance and multidisciplinary intervention in managing rare and life-threatening post-CAR-T complications.