Neurodiagnostics

Clinical Neurophysiology: A Subspecialty of Neurology

The Key to Diagnosis

Key to the diagnosis of many neurological disorders are special tools that help measure how different aspects of the nervous system works. Electroencephalography (EEG) measures brain activity and helps determine the presence of any abnormalities that can predispose to a person to seizures. The electromyography/nerve conduction study (EMG/NCS) measures how well peripheral nerves and muscles are working. Clinical neurophysiology, a subspecialty of neurology, focuses on using these two tools to diagnose seizures and neuromuscular disorders such as neuropathy and carpal tunnel syndrome.

Types of EEG available for outpatients not admitted to the hospital:

• Routine EEG Testing – using recording wires with electrodes, brain waves are monitored for approximately 20 minutes to identify seizures or a risk for seizures.
• Prolonged EEG Testing – when routine testing is not adequate, a longer duration of testing may be necessary to identify seizures or a risk of seizures.

Types of EEG available for outpatients not admitted to the hospital:

• Comprehensive Epilepsy Monitoring Unit – we reserve this test for patients who may qualify for epilepsy surgery or for those whose diagnosis of seizures is unclear or debilitating. These patients are expected to stay in the hospital until enough events are captured to assure their physician that the correct diagnosis and treatment plan are in place. In most cases, patients remain in the epilepsy monitoring unit for three to five days.
• Electrodiagnostic Testing – testing for disorders of the nerves, muscles or neuromuscular junctions.

Electromyography (EMG) & Nerve Conduction Study (NCS) 

These tests can be used to differentiate a problem with the nerves (such as neuropathy) from a problem of the muscles (such as myopathy). Since these tests can be difficult to interpret, they are designated as physician-dependent procedures. Although the tests have technical limitations, they are very useful in detecting conditions that may benefit from specialized treatment, such as chronic inflammatory demyelinating polyradiculoneuropathy (CIDP).

EMG

Electromyography (EMG) is a diagnostic procedure to assess the health of muscles and the nerve cells that control them (motor neurons). Motor neurons transmit electrical signals that cause muscles to contract. An EMG translates these signals into graphs, sounds or numerical values that a specialist interprets.
An EMG uses tiny devices called electrodes to transmit or detect electrical signals. During a needle EMG, a needle electrode inserted directly into a muscle records the electrical activity in that muscle. A nerve conduction study (NCS), another part of an EMG, uses surface electrodes — electrodes taped to the skin — to measure the speed and strength of signals traveling between two or more points. EMG results can reveal nerve dysfunction, muscle dysfunction or problems with nerve-to-muscle signal transmission.

Evoked Potentials

• Visual Evoked potentials – typically used to support a diagnosis of Multiple Sclerosis or Neuromyelitis Optica (Devic’s syndrome)
• Auditory Evoked potentials – typically for patients with hearing loss from nerve damage.
• Somatosensory Evoked Potentials – many uses to evaluate the CNS and Peripheral Nervous System