Neurology · MU Sofia

26. Electromyography

Explains electromyography as a method for assessing muscles and peripheral nerves by recording their electrical activity, and what it helps tell apart: neuropathic, myopathic and neuromuscular junction disorders. Covers needle EMG and nerve conduction studies, normal findings at rest and on contraction, and the EMG patterns of neurogenic, myopathic and junction lesions, with examples of each. Ends with clinical indications and the conduction changes seen in demyelinating and axonal neuropathy.

Inside: 1 section · 1 labelled picture · 13 flashcards · 1 min

Topic 26 of 88 in the MU Sofia syllabus for Neurology (Medicine, Year 4). The free AceMed note covers it in 1 section, about 171 words (1 min of reading), with 13 flashcards.

In this note

  1. Electromyography

Electromyography

Definition: Electromyography (EMG) is a neurophysiological method used to assess the function of muscles and peripheral nerves by recording their electrical activity.

It helps differentiate: Neuropathic disorders. Myopathic disorders. Neuromuscular junction disorders

Types

1. Needle EMG

  • Needle electrode inserted into muscle
  • Records muscle electrical activity at rest and during contraction

2. Nerve Conduction Studies (NCS)

  • Peripheral nerve is electrically stimulated
  • Measures conduction velocity and response amplitude

Normal EMG

  • At Rest: Electrical silence
  • During Contraction: Motor unit action potentials (MUAPs). Increasing activity with stronger contraction

Abnormal Findings

1.Neurogenic (Neuropathic) Lesions

  • Examples: Peripheral neuropathy. Radiculopathy. Motor neuron disease
  • EMG Findings: Fibrillation potentials. Fasciculations. Large, long-duration MUAPs. Reduced recruitment

2.Myopathic Lesions

  • Examples: Muscular dystrophy. Inflammatory myopathies
  • EMG Findings: Small, short-duration MUAPs. Early recruitment

3.Neuromuscular Junction Disorders

  • Example: Myasthenia Gravis
  • Finding: Decremental response on repetitive nerve stimulation

Clinical Indications: Peripheral neuropathies. Radiculopathies. Plexopathies. Motor neuron diseases. Myopathies. Neuromuscular junction disorders. Entrapment neuropathies (e.g., carpal tunnel syndrome)

Nerve Conduction Studies

  • Parameters Measured: Conduction velocity. Latency. Amplitude
  • Demyelinating Neuropathy: Markedly slowed conduction velocity
  • Axonal Neuropathy: Reduced amplitude

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