Opsoclonus-myoclonus-ataxia syndrome in the era of autoimmune encephalitis: reassessment of its rarity and current diagnostic approaches. Cases from clinical practice

Three clinical case reports of opsoclonus-myoclonus-ataxia syndrome (OMAS) in adult patients are presented, illustrating the characteristics of the clinical course, diagnostic challenges and various etiological variants of the condition. In all cases, the onset of the disease was accompanied by the development of ataxia, opsoclonus, myoclonus and cognitive and behavioural disturbances; however, at various stages, the patients were managed under diagnoses of multiple sclerosis, cerebrovascular disease and degenerative disease, which led to a delay in establishing the correct diagnosis. In two patients, the syndrome was paraneoplastic in nature and associated with malignant neoplasms; in one female patient, after the exclusion of a tumour, the condition was classified as seronegative autoimmune OMAS. In all cases, a comprehensive clinical and diagnostic work-up, including magnetic resonance imaging, cerebrospinal fluid analysis, immunological testing and oncological screening, made it possible to exclude alternative causes of the disease and establish the final diagnosis. The initiation of immunosuppressive therapy was accompanied by clinical improvement of varying degrees of severity. The presented case reports emphasize that OMAS in adults remains a rare but likely underestimated condition, requiring high clinical vigilance, timely oncological screening and a comprehensive neuroimmunological work-up. Analysis of these three clinical cases demonstrates the importance of early recognition of the syndrome for the timely initiation of pathogenetic therapy and an improved prognosis.