Progressive supranuclear palsy: clinical features, pathophysiology and management.
Progressive supranuclear palsy (PSP) is a degenerative condition of unknown aetiology that produces an akinetic-rigid form of parkinsonism characterised by early falls and abnormalities of extraocular movements. Mean age of onset is approximately 63 years, and mean survival from symptom onset is 9 years. Men are much more frequently affected than women. The classic clinical finding is supranuclear ophthalmoplegia, which may not present until late in the illness, if at all. The clinical diagnosis of PSP can be difficult to make, as the sites of pathology are heterogeneous. Structural and functional neuroimaging studies, although not specific for PSP, may be of some assistance in making the diagnosis. The definitive diagnosis of PSP requires the presence of both clinical and neuropathological evidence. Multiple anatomical sites are affected in PSP. The most consistently involved are the subthalamic nucleus, globus pallidus interna and externa, pontine nuclei, periaqueductal grey matter and the substantia nigra. The location of the pathology accounts for the clinical features. The histological hallmark of PSP is the presence of globose neurofibrillary tangles in the affected subcortical nuclei. Neurofibrillary tangles are composed of abnormally phosphorylated tau, a microtubule-associated protein that is involved in maintenance of the cytoskeleton. Abnormalities near or in the gene coding for tau are implicated in the pathogenesis of PSP. The multiple neurotransmitter abnormalities, including those affecting dopamine, acetylcholine, gamma-aminobutyric acid and norepinephrine (noradrenaline) systems and pathways, as well as both pre- and post-synaptic pathology, make pharmacological therapy of PSP a challenge. Although an individual patient may respond to a drug, in general patients with PSP have a minimal response and a short duration of sustained benefit.