Single-fiber electromyography (SFEMG)

Single-fiber electromyography (SFEMG) is a specialized diagnostic technique used to assess the function of individual muscle fibers. During single-fiber EMG testing, a series of electrical stimulations, also known as repetitive stimulation, will be delivered to the nerve repeatedly for a few seconds and the responses are recorded from the muscle supplied by that nerve. After the repetitive stimulation, a small needle electrode is inserted into the muscle to record electrical activity. The combination of both parts of the test helps your doctor identify neuromuscular junction disorders.

SFEMG is performed by neurologists or clinicians with expertise in neuromuscular disorders. Penn Medicine is the leading neurology provider in the greater Philadelphia and South Jersey region, and our laboratory is one of the few local facilities to use single-fiber EMG testing to evaluate neuromuscular disorders.

Your Penn Medicine provider may recommend single-fiber EMG testing if you have symptoms of neuromuscular junction conditions, including:

• Myasthenia gravis: This neuromuscular disorder causes muscle weakness and fatigue that is often made worse by activity. It can affect your eye, face, neck, and throat muscles. Single-fiber EMG can help confirm the diagnosis by detecting abnormalities in neuromuscular transmission.
• Lambert-Eaton myasthenic syndrome (LEMS): This autoimmune disorder affects neuromuscular transmission, causing muscle weakness and fatigue, tingling in the hands and feet, bladder and bowel changes, erectile dysfunction, and difficulty breathing, speaking, swallowing, and walking. Single-fiber EMG can aid in the diagnosis of LEMS by detecting characteristic abnormalities in muscle responses.

Your Penn Medicine provider will explain how single-fiber EMG testing works and give you time to ask questions. Your doctor will do a medical history review and physical examination to assess your symptoms. You may be asked to avoid certain medications in the days leading up to your test.

The single-fiber EMG testing process consists of two parts: repetitive nerve stimulation and single-fiber EMG. During single-fiber EMG testing, you can expect the following:

• You'll be asked to lie down on an examination table
• Your neurodiagnostic technologist will clean the skin over the muscles being studied to ensure good electrical contact.
• A brief series of small electrical shocks are applied to a nerve. This electrical stimulation is delivered to the nerve repeatedly for a few seconds and the responses are recorded from the muscle supplied by that nerve.
• A fine needle electrode is inserted into the muscle being examined. This electrode records electrical activity. You're unlikely to feel any pain, but your Penn care team will be by your side the entire time to make sure you'e comfortable.
• The needle electrode records a single motor nerve fiber resulting in electrical activity. The test can take up to one hour.

After the single-fiber EMG test, your Penn Medicine provider may observe you for a brief period, and they'll share any necessary post-procedure instructions. You may experience some mild discomfort or bruising at the site where the electrodes were inserted. This typically resolves within a few hours. In most cases, you can resume your normal activities immediately after the procedure. However, you may be advised to avoid strenuous exercise or activities that could strain the muscles that were tested for a short period of time, depending on your individual circumstances.

Your referring doctor will discuss the results of the single-fiber EMG with you and may recommend further evaluation or treatment based on the findings.