Occult Breast Cancer With Anti-Ri Antibody Positivity and Pontine Hot Cross Bun Sign

A 40-year-old woman presented with gradual-onset pseudobulbar paralysis, diplopia, unsteady walking, and left-sided hearing loss over a 2-year period. Neurological evaluation revealed rotatory nystagmus, limited abduction of the right eye and upward movement of the left eye, decreased muscle strength with normal muscle tone, cerebellar signs, diminished or absent tendon reflexes, and bilateral Babinski sign. Routine and biochemical analyses of cerebrospinal fluid (CSF) samples did not reveal any abnormalities. Serum and CSF samples were negative for oligoclonal bands, anti–myelin oligodendrocyte glycoprotein, and antiganglioside antibodies, including GQ1b, GM1, GM2, GD1, and sulfatides. No thickening was observed on magnetic resonance imaging (MRI) reconstruction of the lumbosacral nerve roots. Needle electromyography revealed fibrillation potentials and positive sharp waves as well as long-duration and high-amplitude motor unit potentials in the muscles of the bulbar, cervical, thoracic, and lumbosacral regions. Anatomical diagnosis was based on analyses of the brain stem, cerebellum, and 4-region motor neurons of the body. An immunotherapeutic regimen consisting of glucocorticoids, immunoglobulin, and plasma exchange failed to achieve satisfactory results.