Bannwarth Syndrome in a Patient With Early-Stage Breast Cancer: An Atypical Manifestation of Lyme Neuroborreliosis.

Neurological symptoms in breast cancer patients can arise from metastasis, medication side effects, or underlying neurodegenerative conditions. When imaging is inconclusive, the more uncommon immune-mediated neuropathies should be considered. Guillain-Barré syndrome and Lyme neuroborreliosis are two immune-mediated conditions that share neurological findings. This case involves a 72-year-old Caucasian female who presented with early-stage invasive ductal carcinoma with neuroendocrine features and gradual bilateral upper extremity weakness and paresthesia. Surgery was uncomplicated, but in the subacute postoperative period, the patient developed progressive worsening of neck and scapular pain, left upper extremity weakness, right-hand paresthesia, and decreased right-hand dexterity. Cervical spine MRI and CT scans of the head and neck areas were insignificant. Leukocytosis, mild hyponatremia, and elevated C-reactive protein were found on laboratory workup. The initial differential diagnosis included paraneoplastic syndromes; however, given the inconclusive imaging, immune-mediated neuropathies, including Lyme neuroborreliosis, were prioritized. A lumbar puncture established the diagnosis of Lyme neuroborreliosis presenting as Bannwarth syndrome, also known as lymphocytic meningoradiculitis. Acute or subacute neurological decline in oncology patients should prompt consideration of paraneoplastic and infectious immune-mediated neurological disorders. Despite its rarity in the United States, Bannwarth syndrome should be considered as a paraneoplastic neuropathy mimic, especially with inflammatory cerebrospinal fluid findings.