Objective: To describe two patients with prostate cancer and identical phenotypes of likely paraneoplastic unilateral leg myoclonus.

Background: Paraneoplastic movement disorders (PMDs) in prostate cancer are rare, and to our knowledge paraneoplastic myoclonus has not been previously reported.

Methods: Case report and literature review.

Results: We report 74- and 76-year-old men with adenocarcinoma of the prostate who developed isolated action myoclonus of unilateral leg, starting 3 weeks and 1 year after the cancer diagnosis, respectively. The phenotypes were very similar in both patients. Myoclonus was not present at rest, but occurred when moving the leg in seated position, and when standing or walking. This limited their ability to ambulate. Extensive evaluation including serum erythrocyte sedimentation rate, cells and protein in cerebrospinal fluid (CSF), paraneoplastic antibodies in serum and CSF was unrevealing. Both had a good response to alcohol, and sodium oxybate was used in one patient with good initial benefit. We review the literature of PMDs in prostate cancer. Videos will be presented.

Conclusions: Myoclonus in our patients was likely paraneoplastic and spinal in origin. Future studies are required to identify exact antigen associated with this unique phenotype. Poor response to immunotherapy may imply intraneuronal, rather than cell surface, antigens. Symptomatic treatment with sodium oxybate may provide benefit and improve quality of life in these patients.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/alcohol-responsive-action-myoclonus-of-the-leg-in-prostate-cancer-a-novel-paraneoplastic-syndrome/