A myogram, also known as an electromyography (EMG), is a diagnostic test performed to assess the health and functionality of an individual's muscles. Conducted to determine the origin of unexplained muscle weakness, an EMG is used to detect conditions such as muscle inflammation, peripheral nerve damage, and muscular dystrophy. As with any medical procedure, there are risks associated with the administration of a myogram and these should be discussed with a qualified health care provider prior to testing.
Individuals experiencing symptoms of muscle weakness or impaired strength may undergo a myogram in order to assess the condition of the affected area. Primarily, the test is administered to determine if the symptoms are neurological in nature or have other origins. Dependent on the location of the muscle weakness, abnormal test results may be indicative of an underlying condition or disorder, including nerve or muscle dysfunction.
Healthy muscles produce no electrical activity while at rest. During physical activity, muscles produce electrical activity, which increases with muscle contraction. When an individual's muscles are damaged or impaired, the electrical activity produced may be hypersensitive, slowed, or somehow inconsistent with expected readings associated with rest and movement. Hypersensitive results may be indicative of a neurological disorder, while a slowed, or decreased, reaction may be characteristic of a myopathic disease.
The myogram testing procedure involves the insertion of a small needle electrode into the affected muscle. Once the needle is in place, it registers the muscle's electrical activity. After base reading is taken while the individual is at rest, he or she may be asked to contract the targeted muscle either by bending or flexing the intended area, such as the leg or arm. The electrical activity produced by the action, referred to as action potential, is interpreted as the muscle's capacity to respond to stimulation. Readings recorded by the needle are transmitted and visually displayed on a monitor, called an oscilloscope, for immediate, preliminary analysis and interpretation.
Prior to the testing process, the individual may feel a bit of discomfort during the preparation phase when the needle is inserted. Risks associated with the administration of a myogram include infection and excessive bleeding at the insertion site. In cases where the muscles sustain trauma during the procedure, inaccurate readings may result during other diagnostic testing procedures, such as muscle biopsies or certain blood tests.
A nerve conduction velocity (NCV) test may be administered prior to or during a myogram in order to evaluate if nerve damage has occurred. Patches containing electrodes are placed on the skin in and around the target area of the EMG. The NCV test measures the speed at which administered electrical impulses pass through the muscle's nerves.
Abnormal test results demonstrating a slowed transmission are indicative of some degree of nerve damage. Common forms of nerve damage found during a NCV include a nerve blockage within the nerve pathway known as a conduction block, or damage to an extended segment of the nerve cell referred to as axonopathy. Though there are no risks associated with this procedure, special precautions must be taken when administering the test on individuals who have a pacemaker or similar implanted cardiovascular device.