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APPROACH TO THE PATIENT: Weakness or Paralysis

Weakness is a reduction of power in one or more muscles. Paralysis indicates weakness that is so severe that the muscle cannot be contracted at all, whereas paresis refers to less severe weakness. The prefix hemi- refers to one half of the body, para- to both legs, and quadri- to all four limbs. The suffix -plegia signifies severe weakness or paralysis.

Increased fatigability or limitation in function due to pain or articular stiffness is often confused with weakness by pts. Increased time is sometimes required for full power to be exerted, and this bradykinesia may be misinterpreted as weakness. Severe proprioceptive sensory loss may also lead to complaints of weakness because adequate feedback information about the direction and power of movements is lacking. Finally, apraxia, a disorder of planning and initiating a skilled or learned movement, is sometimes mistaken for weakness.

The history should focus on the tempo of development of weakness, presence of sensory and other neurologic symptoms, medication history, predisposing medical conditions, and family history.

Weakness or paralysis is typically accompanied by other neurologic abnormalities that help to indicate the site of the responsible lesion (Table 53-1). It is important to distinguish weakness arising from disorders of upper motor neurons (i.e., motor neurons in the cerebral cortex and their axons that descend through the subcortical white matter, internal capsule, brainstem, and spinal cord) from disorders of the motor unit (i.e., lower motor neurons in the ventral horn of the spinal cord and their axons in the spinal roots and peripheral nerves, neuromuscular junction, and skeletal muscle).


Table 53-2 lists common causes of weakness by the primary site of pathology. Table 53-3 summarizes patterns with lesions of different parts of the nervous system.


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