Definition of apraxia and its localizing significance. Examination of praxia

1. Big picture

Apraxia is a disorder of learned purposeful movement. The patient knows what the movement is, wants to do it, and has enough strength and coordination, but cannot correctly perform the learned act on command.

For the neurology exam, apraxia is important because it is a cortical localization sign, not a peripheral motor problem. It usually points to a lesion in the dominant parietal lobe, dominant frontal/premotor region, or the corpus callosum. The lecture also emphasizes that apraxia is mainly a supratentorial sign, not a typical vertebrobasilar/brainstem sign.

The key exam idea is:

Weakness means corticospinal tract / lower motor neuron / muscle problem.
Apraxia means the motor plan cannot be accessed or executed, despite preserved basic motor function.