Objective: We report a case adult onset fulminant SSPE with focal lower limb myoclonus as the predominant presenting movement disorder.

Background: Myoclonus remains a defining clinical feature of SSPE. Although slow, periodic axial myoclonus is considered characteristic of SSPE, atypical forms of myoclonus are increasingly being recognized. We report an adult fulminant SSPE with focal lower limb myoclonus and poor anatomic-radiological correlation.

Method: Case report

Results: A 25-year-old man presented with jerky movements of the right lower limb for three months followed by rapid cognitive decline and akinetic mutism. On examination, he was in a minimally conscious state, exhibiting appendicular rigidity, upper limb dystonia (more pronounced on the right) and focal distal lower limb slow myoclonus. Magnetic resonance imaging revealed asymmetric corpus striatal involvement (right more than left). Electroencephalography (EEG) revealed generalized long-interval periodic discharges, confirming the suspicion of SSPE. Cerebrospinal fluid (CSF) revealed significantly elevated measles IgG antibodies, leading to a diagnosis of fulminant SSPE, Jabbour stage III. Supportive care and isoprinosine was initiated. However, he succumbed to the illness within one month of discharge.

Conclusion: The origin of myoclonus in SSPE remains controversial with variable cephalo-caudal or caudocephalic progression. A brainstem localization of the myoclonus in our patient was suggested by the absence of time-locked EEG correlates of the lower limb myoclonus. Moreover, the myoclonus did not generalize during the disease and showed poor radiological correlation (abnormal striatal hyperintensity ipsilateral to the myoclonus). This case highlights a novel observation of the right lower limb myoclonus superimposed on a dystonic hand.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/focal-lower-limb-myoclonus-heralding-adult-onset-fulminant-sspe/