Progressive Supranuclear Palsy

Progressive supranuclear palsy (PSP) is a sporadic neurodegenerative disorder in which hyperphosphorylated 4-repeat tau accumulates inside neurons and glial cells. Neuronal loss and gliosis affect the globus pallidus, subthalamic nucleus, striatum, substantia nigra, and brainstem tegmentum; later, the frontal cortex and cerebellar dentate nucleus may also be involved. The locations of this injury explain why PSP combines impaired eye movements, axial parkinsonism, postural instability, dysarthria, dysphagia, and frontal-executive change. The word supranuclear describes the level of the eye-movement problem. Voluntary commands to look up or down are impaired, while the brainstem gaze centres and vestibulo-ocular pathways may initially remain relatively intact. Thus, a patient may fail to shift the eyes downward on command but still make a downward reflex eye movement when the head is moved during a clinician-performed examination. This distinction separates a supranuclear disorder from a lesion of the ocular motor nuclei or nerves. Testing should be performed safely and interpreted by the appropriate clinician; a stiff or injured neck is not a reason to provoke a head movement. Vertical gaze palsy is a signature finding, but it...