Principles of neurologic localization.

Organic and nonorganic neurologic conditions can be differentiated by determining whether the symptoms can or cannot be feigned and whether the symptoms make neuroanatomic sense. For localization of organic disease, lower motor neuron signs and dermatome defects suggest peripheral nerves; sensory dissociation points to the spinal cord, and a cranial nerve deficit with a contralateral extremity deficit suggests a brainstem etiology. Higher level, organized dysfunction points to the cerebrum; ataxia during intentional movements indicates cerebellar involvement, and sudden, unintended movements suggest basal ganglia disorders.