Toxoplasma gondii multifocal central nervous system infiltration in an apparently immunocompetent cat in Italy

A young cat with progressive ambulatory deficits with multifocal neurolocalization underwent spinal cord and brain magnetic resonance imaging (MRI). After serological testing through indirect immunofluorescence (IFI; IgG titer = 640, IgM titer = 160; cut-off titer for both = 80) for Toxoplasma gondii and unsuccessful 3-week therapy with clindamycin, his condition worsened. MRI revealed multiple lesions in the cervical and thoracolumbar spinal cord and brain and cerebellum meninges. Subsequent serology revealed low seroconversion (IFI; IgG titer = 1280, negative IgM titer; cut-off titer for both= 80), suggesting chronic infection. Cerebrospinal fluid was negative for T. gondii on PCR. Postmortem histology of the brain and spinal cord confirmed protozoan infiltration. Immunohistochemistry was negative for feline infectious peritonitis but strongly positive for T. gondii. Other infectious agents were not identified. In an apparently immunocompetent young cat with multiple central nervous system inflammatory lesions, without other viral infections, even with low seroconversion, T. gondii differential diagnosis could not be definitively excluded antemortem without biopsy.