Neurophysiology Tests: Electrodiagnostic Study

Principal goal: To localize the neuromuscular disorder
• To localize if the disorder is neuropathic (nerve), myopathic (muscle), a disorder of neuromuscular transmission, or a disorder of the central nervous system (brain and spine)

NCS is a test, which is conducted to assess peripheral nerves in the upper and lower limbs. It measures how electrical impulses are conducting in the nerves. These electrical impulses conduction will be affected and slowed if the nerve is diseased, damaged, injured or compressed.

EMG is a test which is conducted to study the electrical activity of muscle fibers individually and collectively via needle electrode.

NCS- Small sticker electrode is placed on the skin and nerve will be stimulated by electrical current, where the impulse is then recorded. This electrode records the electrical impulse generated by the nerve.

EMG- A small needle electrode is inserted into the muscles where the electric potentials generated will be assessed during needle insertion, during periods of rest and during periods of voluntary muscle contraction.

NCS and EMG are most often used to diagnose disorder of the peripheral nervous system, which include disorders affecting the:

The pattern of nerve conduction abnormality and EMG abnormality usually can differentiate among all the abnormalities mentioned above which then will guide the subsequent laboratory investigations.

Occasionally, information from the electrodiagnostic study (NCS/ EMG) is specific enough to suggests a precise diagnosis.

Radiculopathy

• Disc herniation
• Spondylosis
• Neoplastic
• Inflammatory
• Infarction

Plexopathy

• Radiation induced
• Post traumatic
• Inflammatory
• Entrapment

Neuromuscular Junction Disorder 

• Myasthenia Gravis
• Lambert Eaton syndrome

Myopathy

• Muscle disease- Hereditary and Acquired

• Those with numbness, tingling sensation or feeling abnormal sensation in the hands and legs.
• Muscle weakness, wasting of the muscle, cramps and twitch are also common symptoms that require NCS/ EMG.

A patient who complaint of numbness of the right upper limb, in particular right little and ring fingers with mild neck pain.

Electrophysiologic evaluation: Nerve conduction studies typically are normal, and the electrodiagnosis is established with needle EMG. NCS is important to exclude other conditions that may mimic radiculopathy, especially entrapment neuropathy and plexopathy.

NCS is important to exclude underlying ulnar neuropathy (entrapment neuropathy), and EMG is crucial to exclude underlying C8 radiculopathy as both conditions can present with numbness over the little and ring fingers.