Aug. 30, 2017
Electromyography (EMG) is an essential tool for the diagnosis of patients with neuromuscular disorders. When performed with the required rigor, EMG provides objective measures to complement clinical assessment of patients with complex conditions — information that is critical to confirming or ruling out neuromuscular disorders as well as monitoring progress during treatment.
All three Mayo Clinic campuses have board-certified electrophysiologists and technicians who test patients referred directly for EMG testing from other centers as well as Mayo Clinic patients. In addition to nerve conduction studies and needle examination of common and uncommon nerves and muscles, Mayo Clinic offers specialized tests such as diaphragmatic and peripheral nerve ultrasound, and single fiber EMG.
"Our focus on patient care and attention to detail allow us to provide the highest quality of EMG testing," says Ruple S. Laughlin, M.D., a consultant in Neurology and medical director of the EMG laboratory at Mayo Clinic in Rochester, Minnesota. "The interpretation of needle data can be subjective. We bring finesse and expertise to that interpretation, in addition to technical rigor with testing."
The physicians in the EMG labs at Mayo's three campuses take time and care to focus on every patient's clinical findings as they consider an individual EMG testing plan for each patient. "EMG serves as an extension of the clinical exam," Dr. Laughlin notes. "It can provide more nuance about the location of the problem within the neuraxis, the severity of the condition and even the prognosis for recovery."
"A physician can refer patients to any of our three campuses and know that each EMG lab will use the same protocols, approaches and equipment. We really consider ourselves one lab at three different sites," adds Devon I. Rubin, M.D., a consultant in Neurology and medical director of the EMG laboratory at Mayo Clinic in Jacksonville, Florida.
EMG shows an iterative discharge termed MIRD
Electromyography (EMG) shows an unusual waveform, indicating an iterative discharge identified by Mayo Clinic neurophysiologists and termed motor unit potential induced repetitive discharge (MIRD). MIRDs aren't evoked by an external stimulus but rather are fired semirhythmically with muscle activation and ceased with relaxation, confirming initiation by a voluntary motor unit potential.
Mayo Clinic has a rich history of innovation in EMG, such as the development and enhancement of nerve conduction study techniques and description of a new type of unusual iterative discharge during needle EMG.
As a major academic center with referrals from tertiary institutions, Mayo Clinic has the resources to provide a full range of electrophysiological testing for patients with all types of common and rare neuromuscular disorders, such as neuropathies related to diabetes, chemotherapy, autoimmune neuromuscular diseases, compression, spine-related conditions, and neuromuscular junction diseases such as myasthenia gravis, Lambert-Eaton myasthenic syndrome and congenital myasthenic syndromes.
"We're able to analyze any nerve or muscle problem in detail, including those that require specialized tests," says Mark A. Ross, M.D., a consultant in Neurology and medical director of the EMG laboratory at Mayo Clinic in Phoenix/Scottsdale, Arizona.
Ultrasound of patient's diaphragm
Ultrasound shows the diaphragm of a patient referred for EMG testing for dyspnea.
In addition to routine needle EMG and nerve conduction studies, Mayo Clinic performs:
- Diaphragmatic ultrasound to determine if a neuromuscular problem is causing respiratory weakness
- Ultrasound of the hand to identify carpal tunnel syndrome
- Single fiber EMG, the most sensitive test to confirm or refute a diagnosis of myasthenia gravis
- Cranial nerve testing, to identify nerve root injury or irritation
- Laryngeal EMG, for patients with voice abnormalities or other voice disorders
- Prolonged exercise testing, to detect problems with nerve channels along muscle fibers in patients with episodic weakness
- Cramp-fasciculation testing, to detect peripheral nerve hyperexcitability
Among nonroutine EMG tests, diaphragmatic ultrasound is relatively new but used increasingly at Mayo Clinic. Dr. Ross cites the case of a patient with amyotrophic lateral sclerosis who wanted to enroll in a clinical trial of a diaphragm-pacing system. However, participants in the trial were required to have phrenic nerve responses — which typical nerve conduction studies hadn't detected on one of the patient's sides. Dr. Ross suggested diaphragmatic ultrasound.
"The ultrasound demonstrated that the diaphragm was actually moving quite normally on that side," he says. "So we looked at the phrenic nerve studies again and in fact were able to get a response. That made a big difference for this patient because he was able to join the study."
Ultrasound is also increasingly used to assess compression for median neuropathies or other peripheral nerve lesions. To enhance patients' convenience, Mayo Clinic is initiating point-of-care ultrasound for people with suspected carpal tunnel syndrome. Typically, these patients might have nerve conduction studies and then consult a hand surgeon. To determine eligibility for surgery, the surgeon might recommend ultrasound, which can detect anatomical compression.
"We're streamlining that process," Dr. Laughlin says. "If patients present for carpal tunnel, we can do a focused ultrasound then and there, and provide the additional information to the hand surgeon. That saves the patient a visit and allows the hand surgeon to move forward with treatment."
Partnering for patient care
At Mayo Clinic, EMG technicians are overseen directly by neurophysiologists. Teams of physicians and technicians work together daily, fostering trust and a commitment to quality and patient care.
"Everyone working in the lab has a goal of continuing Mayo's tradition of excellence in EMG and providing the absolute best care for every patient every day," Dr. Rubin says. "We understand that we are seeing patients with very complex disorders whose diagnoses might still be unclear. Our common goal is to ensure exceptional quality in our testing so that we can come to an accurate diagnosis."