What is the role of Electromyography (EMG) in diagnosing Multiple Sclerosis (MS)?

From the Guidelines

Electromyography (EMG) is not typically used as a primary diagnostic tool for multiple sclerosis (MS). While EMG can detect abnormalities in muscle electrical activity and nerve conduction, it has limited value in MS diagnosis because this condition primarily affects the central nervous system (brain and spinal cord) rather than peripheral nerves that EMG best evaluates.

Key Points to Consider

• For diagnosing MS, magnetic resonance imaging (MRI) is the preferred test as it can visualize the characteristic demyelinating lesions in the brain and spinal cord.
• Other more valuable diagnostic tools include cerebrospinal fluid analysis for oligoclonal bands, evoked potential tests (particularly visual evoked potentials), and clinical evaluation of symptoms.
• EMG might occasionally be used in MS patients to rule out other conditions with similar symptoms or to assess secondary effects on peripheral nerves, but it's not part of the standard diagnostic protocol.
• If MS is suspected, patients should be referred to a neurologist who will likely order an MRI and other appropriate tests rather than an EMG, as supported by the MAGNIMS consensus guidelines on the use of MRI in MS 1.
• The use of MRI in MS diagnosis and monitoring has been extensively discussed in various studies, highlighting its importance in establishing disease prognosis and monitoring patients 1.

From the Research

EMG Findings in Multiple Sclerosis

• Electromyographic (EMG) examinations in patients with multiple sclerosis (MS) have shown signs of denervation, which can remit over time 2.
• A study of 29 patients with MS found that 19 patients had no signs of neurogenic atrophy (NA) in involved limbs, while 4 patients had signs of acute NA that disappeared on subsequent examination 2.
• Another study found that EMG abnormalities were present in many MS patients with no concurrent peripheral or entrapment neuropathies, and that electromyographers should be aware of these abnormalities when performing routine EMG examinations in these patients 3.

EMG Abnormalities in MS Patients

• Abnormal late responses with increased amplitude and chronodispersion of F-waves were found in 9 out of 26 MS patients, and abnormal recruitment patterns with decreased numbers of motor unit action potentials (MUAPs) were found in 9 patients 3.
• Single fiber electromyography (SFEMG) showed increased jitter with no blocking in 4 out of 10 MS patients studied 3.
• Spontaneous electromyographic (EMG) activity was found in several muscles with no specific myotomal or peripheral nerve distribution in 5 MS patients 3.

Diagnosis and Treatment of MS

• MS is typically diagnosed based on a combination of signs and symptoms, radiographic findings, and laboratory findings, and treatment options include disease-modifying therapies (DMTs) such as interferons, glatiramer acetate, and teriflunomide 4.
• DMTs have been shown to reduce clinical relapses and MRI lesions in MS patients, with efficacy rates ranging from 29%-68% 4.
• However, the use of DMTs can also be associated with adverse effects such as infections, bradycardia, and infusion reactions 4.