Cortical limb myoclonus in pathologically proven progressive supranuclear palsy

Progressive supranuclear palsy (PSP) is a sporadic tauopathy with insidious onset and a progressive course, first described in 1964 as parkinsonism, postural instability, axial rigidity, supranuclear gaze palsy, pseudobulbar palsy and cognitive changes.[1] However a much broader clinical spectrum is now recognised in association with PSP.[2] PSP may present as corticobasal syndrome (CBS) with asymmetric rigidity, apraxia, dystonia and variable cortical and basal ganglionic features.[3, 4] CBS was first reported in association with the pathological entity of corticobasal degeneration (CBD),[5] but is now recognised to develop secondary to PSP pathology as well as Alzheimers disease, frontotemporal dementia, and other less common causes.[6] This overlap contributes to difficulties with accurate ante-mortem diagnosis of both PSP and CBD. It has been suggested that myoclonus favours the likely pathological diagnosis of CBD rather than PSP,[7, 8] although very few pathologically proven cases of PSP have documented myoclonus.[9, 10] We report the clinical and neurophysiological features of cortical myoclonus in a patient with pathologically proven PSP, in order to highlight the clinical features that are helpful in distinguishing CBS arising from PSP compared with CBD pathology