Leptomeningeal carcinomatosis is a serious complication of advanced cancer. Various clinical manifestations may present, such as headache, nausea, seizures, cranial neuropathies. In this article, we report the case of a 65-year-old woman with metastatic breast cancer who was admitted to hospital suffering from facial palsy, which was suspected to be caused by leptomeningeal tumor infiltration. Magnetic resonance imaging (MRI) scans of the head and spine showed meningeal enhancement of the facial nerve, conus medullaris, and fibers of the cauda equina, which were radiologically interpreted as leptomeningeal carcinomatosis. Assessment of cerebrospinal fluid found no malignant cells but investigation for infectious diseases established the diagnosis of neuroborreliosis. Antibiotic treatment with doxycycline was performed. After completion of treatment, follow-up MRI scans found complete regression of meningeal enhancement. Several months later, the patient is still in good condition and without neurological symptoms. Hence, initial diagnosis of leptomeningeal carcinomatosis was rejected. This case report should alert oncologists to carefully rule out infectious diseases before leptomeningeal carcinomatosis is diagnosed. Cerebrospinal fluid analysis is strongly recommended due to low specificity of MRI images in this regard.