A rare case of T-cell CNS Lymphoma mimicking tacrolimus neurotoxicity

<h3></h3> A 44-year-old, post-transplant female, presented with urosepsis and raised tacrolimus level. She developed focal motor seizures. She suffered long-standing type-1 diabetes, developing end-stage renal disease and requiring kidney transplantation in her teenage years. Expressive aphasia and right hemiparesis were evident on examination. Serum Tacrolimus level was 27.6 µg/L (therapeutic range 5–15), Creatinine 394 µmol/L and eGFR 11. Radiology opinion of non-contrast MRI head considered tacrolimus neurotoxicity and PRES, acknowledging that infective/inflammatory pathology could not be ruled out. CSF analysis demonstrated WCC 12, protein 0.32 g/L, glucose 4.1. Extensive CSF infective and autoantibody screening was negative. EEG showed encephalopathy. She was covered with IV Cefuroxime and Ganciclovir. Tacrolimus was withheld, due to concerns of tacrolimus neurotoxicity, while levetiracetam was commenced, and her condition improved. Contrast MRI head 6 weeks later demonstrated nodular and ring-enhancing lesions, with leading differential of lymphoma versus toxoplasmosis or tuberculosis. Repeat CSF showed WCC 4, protein 0.62 g/L, glucose 4.5. PET-CT showed isolated metabolically active brain lesions. She received empirical antibiotics and underwent brain biopsy confirming malignant T-cell lymphoma, though died 1 week later. This case highlights the importance of remaining highly vigilant for lymphoma in immunosuppressed patients and considering early re-imaging without contrast in renal impairment.