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Etiology and evaluation of the child with weakness

Russell Migita, MD
Section Editor
George A Woodward, MD
Deputy Editor
James F Wiley, II, MD, MPH


The approach to the child with weakness will be reviewed here. The approach to an infant or newborn with hypotonia or weakness is discussed separately. (See "Approach to the infant with hypotonia and weakness" and "Overview of peripheral nerve and muscle disorders causing hypotonia in the newborn".)


Weakness is a decreased ability to voluntarily and actively move muscles against resistance. Weakness may arise from any portion of the motor unit and is typically divided into upper motor neuron and lower motor neuron weakness as follows:

Upper motor neuron weakness – Upper motor neuron weakness arises from lesions in the cerebral cortex and corticospinal tracts down to, but not including, the anterior horn cell in the dorsal spinal cord.

Lower motor neuron weakness – Lower motor neuron weakness results from lesions located in the anterior horn cell, peripheral nerve, neuromuscular junction, or muscle.

Weakness can be confused with hypotonia or ataxia. Hypotonia is a decreased resistance to passive range of motion. Ataxia refers to decreased muscular coordination. (See "Approach to the infant with hypotonia and weakness" and "Approach to the child with acute ataxia".)

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Literature review current through: Nov 2017. | This topic last updated: Aug 21, 2017.
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