A case report of sporadic Creutzfeldt–Jakob disease presenting with progressive opsoclonus–myoclonus–ataxia-Plus (OMAS-Plus) phenotype

Background Sporadic Creutzfeldt–Jakob disease (sCJD) is a rapidly progressive prion disorder whose heterogeneous manifestations may overlap with potentially treatable neurological conditions. We report an atypical sCJD phenotype dominated by progressive dysarthria and an opsoclonus–myoclonus–ataxia-plus (OMAS-plus) phenotype, highlighting the diagnostic pitfalls relative to treatable mimics.Case presentation A 63-year-old man presented with progressive dysarthria and bulbar symptoms suggesting myasthenia gravis, but did not improve on pyridostigmine and progressed to right-predominant hemiataxia, acral polymyoclonus, dystonia, pyramidal signs, facial palsy, and cognitive–behavioural decline. Video-oculography showed opsoclonus, upbeat nystagmus, and abnormal saccades, raising suspicion of an immune-mediated or paraneoplastic OMAS-plus; extensive autoimmune, paraneoplastic, infectious, metabolic, and neuromuscular work-up was unrevealing, and empirical corticosteroids produced no improvement. EEG lacked periodic sharp-wave complexes and CSF 14–3-3 was negative; PRNP sequencing showed a codon 129 methionine-homozygous genotype without pathogenic mutation. Brain MRI showed cortical and basal ganglia DWI/FLAIR hyperintensities, CSF RT-QuIC was positive, and neuropathological examination, together with a type 1 PrP^Sc Western blot profile, confirmed sCJD of the MM1 subtype.Discussion An OMAS-plus presentation may occur in sCJD and may initially direct diagnostic reasoning towards potentially treatable disorders. Rapid progression, absent support for alternative diagnoses, characteristic MRI abnormalities, and RT-QuIC positivity should prompt consideration of prion disease even when conventional supportive markers are non-diagnostic.