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Harrison's Principles of Internal Medicine, 18e
| Part 2. Cardinal Manifestations and Presentation of Diseases > Section 3. Nervous System Dysfunction > |
Chapter 22. Weakness and Paralysis
Sections: Weakness and Paralysis: Introduction.
Topics Discussed: muscle weakness; neuromuscular weakness; paralysis.
Excerpt:"Normal motor function involves integrated muscle activity that is modulated by the activity of the cerebral cortex, basal ganglia, cerebellum, and spinal cord. Motor system dysfunction leads to weakness or paralysis, which is discussed in this chapter, or to ataxia (Chap. 373) or abnormal movements (Chap. 372). The mode of onset, distribution, and accompaniments of weakness help suggest its cause.This pattern of weakness results from disorders that affect the upper motor neurons or their axons in the cerebral cortex, subcortical white matter, internal capsule, brainstem, or spinal cord (Fig. 22-1). These lesions produce weakness through decreased activation of the lower motor neurons. In general, distal muscle groups are affected more severely than are proximal ones, and axial movements are spared unless the lesion is severe and bilateral. With corticobulbar involvement, weakness usually is observed only in the lower face and tongue; extraocular, upper facial, pharyngeal, and jaw muscles almost always are spared. With bilateral corticobulbar lesions, pseudobulbar palsy often develops: dysarthria, dysphagia, dysphonia, and emotional lability accompany bilateral facial weakness and a brisk jaw jerk. Spasticity accompanies upper motor neuron weakness..."
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