Weakness & Paralysis

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

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