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Abstract
We present data from a follow-up study of two patients affected by a degenerative disorder of the central nervous system (cortico-basal degeneration). At the onset, they both complained of clumsiness in performing fine finger movements, which disturbed daily activities. In one patient, the right hand was affected, while in the other patient the left hand was involved. In both cases, we found apractic deficit which was consistent across all gesturing tasks and generalized to proximal movement and to the other side during follow-up. Preserved knowledge of tool function and use, and unimpaired gesture recognition, were found even in the later stages of the disease. These findings fulfilled Liepmann's criteria for the diagnosis of limb-kinetic apraxia. Qualitative analysis of performance on the apraxia tests showed a considerable distal/proximal dichotomy, i.e. greater difficulties in performing fine finger movements than arm trajectories. Furthermore, the two patients had greater difficulty in carrying out motor sequences than holding a position. These findings, together with previous cases in the literature, are in agreement with recent neurophysiological and positron emission tomography studies showing anatomical segregation for proximal and distal components of the action execution system and multiple neural mechanisms of the action recognition system.