Rationale: Anti-Ri paraneoplastic neurological syndrome (PNS) is typically associated with brainstem or cerebellar involvement and often linked to breast cancer. Cortical involvement is rare and not well documented. We report a unique case of anti-Ri-associated neocortical encephalitis mimicking a brain tumor, broadening the clinical spectrum of anti-Ri PNS.
Methods:
A previously healthy 54-year-old woman experienced multiple brief episodes of altered behavior, confusion, and motor aphasia—described as freezing during payment, placing an egg with the shell into a pan, and forgetting how to hail a taxi. Each episode lasted several minutes and resolved spontaneously, raising clinical concern for focal onset seizures with impaired awareness. Neurological exam was normal, but brain MRI showed a non-enhancing tumefactive lesion in the right frontal cortex with diffusion restriction and FLAIR hyperintensity. MR spectroscopy showed borderline elevation of the Cho/Cr ratio, raising suspicion for a low-grade glioma. A stereotactic brain biopsy was performed. Further workup included CSF analysis, paraneoplastic antibody panel, and systemic malignancy screening.
Results: The biopsy revealed perivascular lymphocytic infiltration without evidence of malignancy. CSF showed mild pleocytosis and was negative for infection. Serum paraneoplastic antibody screening revealed strong anti-Ri positivity. Systemic imaging identified ER/PR-positive right breast cancer with axillary lymph node metastasis. Based on the PNS-Care criteria—incorporating a high-risk antibody and an associated malignancy—a diagnosis of definite anti-Ri PNS was made. The patient received high-dose intravenous methylprednisolone (1 g/day for 5 days) followed by four weekly rituximab infusions. Follow-up MRI showed complete resolution of the cortical lesion, and she remained neurologically asymptomatic.
Conclusions: This case highlights an atypical presentation of anti-Ri PNS with isolated frontal cortical involvement and seizure-like symptoms. Cortical expression of NOVA2, one of the anti-Ri antibody targets, may account for this unusual phenotype. To our knowledge, this is the first reported case of anti-Ri-associated encephalitis presenting with frontal neocortical involvement and seizure semiology. The case supports the need to consider paraneoplastic encephalitis in the differential diagnosis of tumor-like cortical lesions and to remain vigilant for seizure presentations in PNS, even in the absence of classical brainstem signs.
Funding:
This research received no external funding.