Clinical spectrum and diagnostic pitfalls of neurologic syndromes with Ri antibodies.

To describe the main syndrome and clinical course in a large cohort of patients with anti-Ri-associated paraneoplastic neurologic syndrome (Ri-PNS).Twenty-year retrospective nationwide study and systematic review of the literature.Thirty-six patients with complete clinical information were identified (median age 66 years, range: 47-87 years). In this French cohort, the majority were women (78%). At onset, 4 main patterns were observed: cerebellar syndrome (39%), isolated tremor (24%), oculomotor disturbances (17%), and other symptoms (19%). Course was multistep for 78% of cases. At the time the disease reached the plateau phase (median 12 weeks, range: 1-64 weeks; 28% >3 months), 24 (67%) showed an overt cerebellar syndrome, which was isolated in 3 patients, and was most frequently (21/24 cases) part of a multisystem neurologic disease. Patients manifested a variety of movement disorders, including myoclonus (33%), dystonia (17%), either cervical or oromandibular, and parkinsonism (17%). Most patients had cancer (92%), mainly breast cancer (n = 22). Misdiagnoses concerned 22% of patients (n = 8) and included atypical parkinsonism (n = 2), MS (n = 2), Bickerstaff encephalitis (n = 1), hyperekplexia (n = 1), vestibular neuritis (n = 1), and functional neurologic disorder (n = 1). Survival at 12 months was 73% (95% CI [0.54-0.85]), at 24 months 62% (95% CI [0.41-0.78]), and at 36 months 47% (95% CI [0.25-0.65]). There was no major clinical difference between cases retrieved from the systematic review of the literature (n = 55) and the French cohort.Ri-PNS is a multisystem neurologic syndrome with prominent cerebellum/brainstem involvement. Opsoclonus-myoclonus is less common than expected, and the disorder can mimic neurodegenerative diseases.