How does electromyography help distinguish muscle disease from nerve disease?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

muscle disease The causative agent of tetanus, *Clostridium tetani*.

Electromyography (EMG) distinguishes between muscle disease and nerve disease by measuring the electrical activity of muscles using a needle electrode. By analyzing these signals during relaxation, voluntary contraction, and nerve stimulation, physicians can identify the source of muscle weakness.1

The diagnostic patterns differ significantly between the two conditions:

Neuropathic disorders (nerve disease): These conditions typically present with increased spontaneous electrical activity during muscle relaxation, such as fibrillation and fasciculation. Additionally, normal muscle action potentials are often reduced, altered, or absent.1
Myopathies (primary muscle disease): These conditions are frequently characterized by a reduction in the amplitude or duration of muscle action potentials, alongside an increase in the complexity of their waveform.1

By observing these distinct electrical signatures, clinicians can determine whether weakness stems from impaired nerve supply or intrinsic myopathy.1