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For further information, see CMDT Part 24-07: Weakness & Paralysis

Key Features

  • Loss of muscle power may result from

    • Central disease involving the upper or lower motor neurons

    • Peripheral disease involving the roots, plexus, or peripheral nerves

    • Disorders of neuromuscular transmission

    • Primary disorders of muscle

Clinical Findings

  • Weakness resulting from upper motor neuron lesions

    • Characterized by selective involvement of certain muscle groups

    • Associated with spasticity, increased tendon reflexes, and extensor plantar responses

  • Lower motor neuron lesions

    • Lead to muscle wasting as well as weakness, with flaccidity and loss of tendon reflexes

    • However, no change in the plantar responses unless the neurons subserving them are directly involved

    • Fasciculations may be evident over affected muscles

  • In distinguishing between a root, plexus, or peripheral nerve lesion, the distribution of the motor deficit and of any sensory changes is of particular importance

  • In disturbances of neuromuscular transmission, weakness is

    • Patchy in distribution

    • Often fluctuates over short periods of time

    • Not associated with sensory changes

  • In myopathic disorders, weakness is

    • Usually most marked proximally in the limbs

    • Not associated with sensory loss or sphincter disturbance

    • Not accompanied by muscle wasting or loss of tendon reflexes, at least not until an advanced stage


  • See individual disorders


  • See individual disorders

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