A degenerative disease of the central nervous system characterized by balance difficulties; ocular motility disorders (supranuclear ophthalmoplegia); dysarthria; swallowing difficulties; and axial dystonia. Onset is usually in the fifth decade and disease progression occurs over several years. Pathologic findings include neurofibrillary degeneration and neuronal loss in the dorsal mesencephalon; subthalamic nucleus; red nucleus; pallidum; dentate nucleus; and vestibular nuclei. (From Adams et al., Principles of neurology, 6th ed, pp1076-7)