Neuromyotonia is a rare acquired peripheral nerve hyper-excitability disorder that is characterized by spontaneously occurring muscle activity of peripheral nerve origin. 40% of neuromyotonia cases are associated with antibodies to voltage-gated potassium channels (VGKC) as an acquired paraneoplastic syndrome. In this case report, we present a patient presenting with neuromyotonia and progressive encephalopathy with underlying metastatic prostate adenocarcinoma and positive voltage-gated calcium channel (VGCC) antibodies.

A 78-year-old male with a history of seizure disorder and chronic subdural hematoma presented to the hospital with left-sided facial twitching affecting his speech. Electroencephalogram was unremarkable. Magnetic resonance imaging of the brain with gadolinium contrast revealed a small area of restricted diffusion without apparent diffusion coefficient correlation over the right perisylvian area, possibly due to an inflammatory or autoimmune response. Cerebrospinal fluid was positive for N- type VGCC antibodies. Electromyography demonstrated diffuse polyphasic bursts with intermittent sustained myotonic discharges in multiple muscles. He was treated with human intravenous immunoglobulin (IVIG) therapy followed by corticosteroids for a presumptive autoimmune neuromuscular process with significant improvement of symptoms and muscle hyperactivity after initial induction course. Several months later, he developed worsening lower extremity weakness and numbness, worsening myotonia, and was also found to have sclerotic bone lesions consistent with stage 4 prostate adenocarcinoma. His symptoms continued to progress despite IVIG and plasmapheresis, and he was eventually transitioned to hospice care and passed away.

While most cases of paraneoplastic neuromyotonias are associated with VGKC antibodies, this is the first known case describing a possible association with VGCC antibodies. Furthermore, while acquired neuromoytonia syndromes are typically found in association with solid chest tumors (especially thymoma), this is the first documented case of a paraneoplastic neuromytonia associated with prostate adenocarcinoma; the correlation is strengthened by an apparent temporal association between spread of cancer and worsening of neuromyotonia.