This 81-year-old man noted that he “lost use of my left arm” 3 years prior to this evaluation.

It started with tremor and posturing but evolved into progressive difficulties with moving the left arm at will, and eventually, it interfered with the action of the opposite hand. Over time, he also noted that the left leg became weak and incoordinated. Two years into his illness, he needed a walker and, shortly thereafter, a wheelchair for ambulation. His speech volume softened and his swallowing slowed, requiring him to clear his throat often. Prior medication trials with levodopa, amantadine, tizanidine, and baclofen failed due to the development of light-headedness or drowsiness.

The presence of a rapidly progressive and profoundly asymmetric akinetic-rigid syndrome with severe arm dystonia and rigidity, postural tremor, stimulus-sensitive myoclonus, and historic evidence of arm levitation (alien limb syndrome), in the setting of sensory extinction and severe position loss in the left arm suggested the presence of a corticobasal syndrome (CBS). Cognitive impairment meeting criteria for mild dementia was detected at by bedside screening (Mini-Mental State Examination [MMSE] = 21/30; Frontal Assessment Battery = 16/18; abnormal clock drawing). The brain magnetic resonance imaging (MRI) demonstrated asymmetric focal atrophy, greater in the right parietal and, to a lesser extent, temporal lobes, with corresponding mild ex vacuo enlargement of the occipital horn of the right lateral ventricle.

Major features of CBS are early postural and gait impairment, asymmetric bradykinesia, rigidity, dystonia (with or without an “alien limb” phenomenon), postural and kinetic tremor, and later cortical deficits (progressive ideomotor apraxia, aphasia, astereognosis, and agraphesthesia). Our patient’s high-frequency, high-amplitude unilateral tremor, occurring intermittently at rest and on posture, suggested a pathology of corticobasal degeneration (CBD), which is absent in all cases of CBS due to pathology-proven AD, a major cause of CBS (Fig. 57.1) (see second video). The other clinical features of CBS, including ideomotor and limb kinetic apraxia (confirmed before dystonia and rigidity become severe) and action and stimulus-sensitive myoclonus, have been reported in a range of disorders including vascular parkinsonism, AD, progressive supranuclear palsy
(PSP), Creutzfeldt-Jakob disease, dementia with Lewy bodies, and frontotemporal dementia. In fact, most cases of CBS are due to PSP rather than CBD pathology. These CBS-PSP cases tend to have delayed onset of vertical supranuclear gaze palsy (greater than 3 years after onset of first symptom) and rarely have predominant downgaze abnormalities.