Paraneoplastic neurological syndromes are very rare and often associated to breast, ovarian and small cells lung cancers. Paraneoplastic motor neuron diseases (MNDs) are even rarer, and frequently described in patients with breast cancer. We presented the first case of patient affected by HER2-positive breast tumor and possible paraneoplastic lower motor neuron disease. In literature, few cases are reported but no one highlights the tumor receptors' profile. Instead, HER2-positive breast cancers are prone to be related to anti-Yo-associated paraneoplastic cerebellar disorders. Anti-onconeural antibodies positivity can be rarely found, confirming that paraneoplastic MND have no specific biomarkers. The presence of CSF oligoclonal bands (OBs) suggests the presence of immune-mediated mechanism, in absence of other possible OBs causes.