Testing may take 30-60 minutes. The nerve conduction part of the test usually takes longer than the needle exam because one needs to make calculations and measurements during it. On average, if one extremity is studied, the nerve conductions take anywhere between 15 and 30 minutes. The needle exam for one extremity usually takes 15 to 20 minutes. You can count on being in the examination room for about one hour if only one extremity is requested; longer if more extremities need to be tested.

A minimal evaluation for radiculopathy includes 1 motor and 1 sensory NCS and a needle EMG examination of the involved limb. However, the EDX testing can include up to 3 motor NCSs (in cases of an abnormal motor NCS, the same nerve in the contralateral limb and another motor nerve in the ipsilateral limb can be studied) and 2 sensory NCSs. Bilateral studies are often necessary to exclude a central disc herniation with bilateral radiculopathies or spinal stenosis or to differentiate between radiculopathy and plexopathy, polyneuropathy, or mononeuropathy.

H reflexes and F waves can provide useful complementary information that is helpful in the evaluation of suspected radiculopathy and can add to the certainty of electrodiagnostic information supporting a diagnosis of root dysfunction.

Additional testing may be indicated in patients with a differential diagnosis which includes peripheral neuropathy, cervical radiculopathy, brachial plexopathy, or more proximal median neuropathy.

To determine the level of the lesion in a focal mononeuropathy, and in order to exclude radiculopathy, plexopathy, or polyneuropathy, it may be necessary to study 3 motor and 3 sensory nerves including the clinically affected nerve, the same nerve on the contralateral side, and an unaffected ipsilateral nerve. F-wave studies provide additional diagnostic information. A needle EMG examination in the affected limb is indicated.

In order to characterize the nature of the polyneuropathy (axonal or demyelinating, diffuse or multifocal) and in order to exclude polyradiculopathy, plexopathy, neuronopathy, or multiple mononeuropathies, it may be necessary to study 4 motor and 4 sensory nerves, consisting of 2 motor and 2 sensory NCSs in 1 leg, 1 motor and 1 sensory NCS in the opposite leg, and 1 motor and 1 sensory NCS in 1 arm. H-reflex studies and F-wave studies from 2 nerves may provide additional diagnostic information. At least 2 limbs should be studied by a needle EMG examination. Studies of related paraspinal muscles are indicated to exclude some conditions such as polyradiculopathy.

To diagnose a myopathy, a needle EMG examination of 2 limbs is indicated. To help exclude other disorders such as polyneuropathy or neuronopathy, 2 motor and 2 sensory NCSs are indicated. Two repetitive motor nerve stimulation studies may be performed to exclude a disorder of neuromuscular transmission.

In order to establish the diagnosis of motor neuronopathy (for example, amyotrophic lateral sclerosis [ALS or Lou Gehrig’s disease]) and to exclude other disorders in the differential diagnosis, such as multifocal motor neuropathy or polyneuropathy, up to 4 motor nerves and 2 sensory nerves may be studied. Needle EMG of up to 4 extremities (or 3 limbs and facial or tongue muscles) is often necessary to document widespread denervation and to exclude a myopathy. One repetitive motor nerve stimulation study may be indicated to exclude a disorder affecting neuromuscular transmission.

To characterize a brachial plexopathy and to differentiate it from cervical radiculopathy and mononeuropathies, it is often necessary to study all major sensory and motor nerves that can be easily studied in both upper extremities (radial, median, ulnar, and medial and lateral antebrachial cutaneous sensory; radial, median, ulnar, and possibly axillary and musculocutaneous motor) and to perform a needle EMG examination in both upper extremities. To characterize the lumbosacral plexopathy and to differentiate it from lumbar radiculopathy and mononeuropathies, it is often necessary to study all major sensory and motor nerves that can be easily studied in both lower extremities (superficial peroneal and sural sensory; peroneal and posterior tibial motor) and to perform a needle EMG examination in both lower extremities. F-wave studies in the motor nerves and soleus H reflexes also provide useful information.

To demonstrate and characterize abnormal neuromuscular transmission, repetitive nerve stimulation studies should be performed in up to 2 nerves and SFEMG in up to 2 muscles. If any of these are abnormal, up to 2 motor and 2 sensory NCSs may be performed to exclude neuropathies that can be associated with abnormal neuromuscular transmission. At least 1 motor and 1 sensory NCS should be performed in a clinically involved limb, preferably in the distribution of a nerve studied with repetitive stimulation or SFEMG. At least 1 distal and 1 proximal muscle should be studied by a needle EMG examination to exclude a neuropathy or myopathy that can be associated with abnormal repetitive stimulation studies or SFEMG. At least 1 of the muscles should be clinically involved and both muscles should be in clinically involved limbs.

In combination, NCSs and a needle EMG examination may be most helpful when performed several weeks after the injury has occurred. However, NCSs are often useful acutely after nerve injury, for example, if there is concern that a nerve has been severed. In fact, if studies are delayed, the opportunity to precisely identify the region of injury or to intervene may be lost. In some cases, even needle EMG testing performed immediately after a nerve injury may demonstrate abnormal motor unit action potential (MUAP) recruitment and/or provide baseline information that can be helpful in documenting preexisting conditions, date the injury, or serve as a baseline for comparison with later studies.

Because of the variability of different nerve injuries, a standard rule on the timing of EDX testing cannot easily be established and the AAEM does not have specific recommendations in this regard. In all instances, the AAEM encourages dialogue between physicians and payors and encourages the appropriate use of the physician’s clinical judgment in determining when studies are most appropriately performed and what studies should be conducted.

There are many clinical situations where good medical management requires repeat testing, such as in the following examples:

• Second diagnosis. Where a single diagnosis is made on the first visit, but the patient subsequently develops a new set of symptoms, further evaluation is required for a second diagnosis.
• Inconclusive diagnosis. When a serious diagnosis (e.g., ALS) is suspected but the results of the needle EMG/NCS examination are insufficient to be conclusive, 1, or even more, follow-up studies are needed to establish or exclude the diagnosis.
• Rapidly evolving disease. Initial EDX testing in some diseases may not show any abnormality (e.g., Guillain-Barré syndrome) in the first 1 to 2 weeks. An early diagnosis confirmed by repeat electrodiagnosis must be made quickly so that treatment can begin. Follow-up testing can be extremely useful in establishing prognosis and monitoring patient status.
• Course of the disease. Certain treatable diseases such as polymyositis and myasthenia gravis follow a fluctuating course with variable response to treatment. The physician treating such patients needs to monitor the disease progress and the response to therapeutic interventions. The results of follow-up evaluations may be necessary to guide treatment decisions.
• Unexpected course or change in course of the disease. In certain situations, management of a diagnosed condition may not yield expected results or new, questionably related problems may occur (e.g., failure to improve following surgery for radiculopathy). In these instances, reexamination is appropriate.
• Recovery from injury. Repeat evaluations may be needed to monitor recovery, to help establish prognosis, and/or to determine the need for and timing of surgical intervention (e.g., traumatic nerve injury).

Repeat EDX consultation is therefore sometimes necessary and, when justifiable, should be reimbursed. Reasonable limits can be set concerning the frequency of repeat EDX testing per year in a given patient by a given EDX consultant for a given diagnosis. The following numbers of tests per 12-month period per diagnosis per physician are acceptable:

• Two tests for carpal tunnel-unilateral, carpal tunnel-bilateral, radiculopathy, mononeuropathy, polyneuropathy, myopathy, and NMJ disorders.
• Three tests for motor neuronopathy and plexopathy.

Spinal nerves have motor fibers and sensory fibers. The motor fibers innervate certain muscles, while the sensory fibers innervate certain areas of skin. A skin area innervated by the sensory fibers of a single nerve root is known as a dermatome. A group of muscles primarily innervated by the motor fibers of a single nerve root is known as a myotome. Although slight variations do exist, dermatome and myotome patterns of distribution are relatively consistent from person to person.

The ventral (anterior) gray matter of the spinal cord contains nerve cells that send axon fibers out, through the nerves, to their end points on the muscles that they activate. Sensory information from the body and arriving instructions from the brain all cause movement by giving instructions to these “motor neurons” in the spinal cord gray matter.