A novel antineuronal antibody in a motor neuron syndrome associated with breast cancer.

A 72-year-old woman developed a lower motor neuron syndrome (MNS) 4 months before the appearance of breast cancer. Monoparesis progressed to quadriparesis despite high-dose IV immunoglobulins, plasma exchange, and azathioprine, and high-dose IV methylprednisolone. The patient improved only after the removal of the tumor. MRI demonstrated hyperintensities in the cervical spinal cord. The patient had antibodies that reacted with axonal initial segments and nodes of Ranvier. The findings suggest that in this patient lower MNS may be a paraneoplastic condition associated with breast cancer.