Occult breast carcinoma presenting as paraneoplastic opsoclonus-myoclonus-ataxia syndrome

Opsoclonus-myoclonus-ataxia syndrome (OMAS) is a rare immune-mediated neurological disorder in adults and is frequently associated with an underlying malignancy. We report a woman in her sixties presenting with subacute onset opsoclonus and gait ataxia. Diagnostic evaluation identified metastatic carcinoma involving the left axillary lymph nodes. No primary breast lesion was detected on mammography, ultrasonography, positron emission tomography-computed tomography or contrast-enhanced breast MRI. Paraneoplastic antibody panels in both serum and cerebrospinal fluid were negative. Marked neurological improvement was observed following treatment with corticosteroids and intravenous immunoglobulin. This case illustrates an uncommon presentation of antibody-negative paraneoplastic OMAS associated with occult breast carcinoma manifesting solely as axillary nodal disease.