Bilateral visual impairment caused by Toxoplasma gondii encephalitis and ocular GVHD in a patient after allo-HSCT

Cerebral toxoplasmosis is a rare but potentially fatal opportunistic infection in non-HIV immunocompromised patients, particularly after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Diagnosis is often delayed due to nonspecific clinical manifestations. We report a 66-year-old man with myelodysplastic syndrome that had transformed into secondary acute myeloid leukemia. Following remission induction with CPX-351, he underwent allo-HSCT and received ciclosporin A, mycophenolate mofetil, and corticosteroids for graft-versus-host disease prophylaxis. Standard cotrimoxazole prophylaxis was withheld because of hepatic intolerance and thrombocytopenia, and inhaled pentamidine was administered instead. Three months post-transplant, the patient presented with bilateral visual field deficits. Automated perimetry revealed a homonymous inferior quadrantanopia. Brain MRI demonstrated a solitary ring-enhancing lesion in the left optic radiation, and cerebrospinal fluid PCR confirmed Toxoplasma gondii. Treatment with sulfadiazine, pyrimethamine, and folinic acid was initiated, followed by long-term secondary prophylaxis. Despite residual visual impairment, the patient achieved clinical stability. This case underscores the diagnostic value of neuro-ophthalmologic examination and early neuroimaging in detecting opportunistic CNS infections. It also highlights the challenges of prophylactic decision-making in immunocompromised patients when cotrimoxazole is contraindicated. Individualized immunosuppressive and prophylactic strategies, along with multidisciplinary care, were key to successful management.