EMG video gallery

This EMG show cases normal recruitment in a muscle with voluntary activation.

This is an EMG showing only one MUAP with activation. This is consistent with severe muscle denervation. This patient in this case had ALS.

End-plate noise occurs when the tip of the EMG needle is within a neuromuscular junction/close to a motor end plate. On EMG, It is best described as low amplitude, irregular waves. Audibly, it sounds comparable to that of a seashell (listening to the ocean). This is considered a normal EMG finding.

Positive waves and fibrillations are rhythmic discharges of individual muscle fibers representing active denervation. Fibrillations and positive waves are usually not seen until 7 to 10 days after the onset of injury.

Positive waves can be differentiated from fibrillations due to their initial positive deflection and longer duration. While positive waves and fibrillations have different morphologies, they have the same clinical significance.

Positive waves represent active denervation and are usually not seen until 7 to 10 days after onset of injury. Positive waves and fibrillations have the same clinical significance and can be differentiated from each other easily; positive waves have an initial positive deflection and are longer in duration than fibrillations.

This EMG shows irregular spontaneous firing of motor neurons which are called fasciculations. Audibly, it can be compared to popcorn popping in the microwave. Fasciculations can be normal and benign if rare, but when they are frequent, they can represent acute muscle denervation. Widespread fasciculations involving many muscles can be appreciated with motor neuron disease (ALS), benign fasciculation syndrome, and cramp fasciculation syndrome.

This EMG shows irregular spontaneous firing of motor neurons which are called fasciculations of the right tibialis anterior muscle. Audibly, it can be compared to popcorn popping in the microwave. Fasciculations can be normal and benign if rare, but when they are frequent, they can represent acute muscle denervation. Widespread fasciculations involving many muscles can be appreciated with motor neuron disease (ALS), benign fasciculation syndrome, and cramp fasciculation syndrome.

Myotonic discharges have audio characteristics of a “dive bomber”, described as an accelerating and decelerating motorcycle engine. Myotonia is the incomplete relaxation of muscle following contraction of direct muscle percussion. Myotonia can be secondary to a wide range of myopathic disorders including myotonic dystrophy, myotonia congenita, periodic paralysis, Pompe disease, and toxic myopathy.

Myokymia is the rhythmic firing of grouped motor units, especially in doublets or triplets. Audibly it has been compared to the sound of marching soldiers. This can be seen in post-radiation neuropathy/plexopathy.

Polymyositis and dermatomyositis are idiopathic inflammatory myopathies. On EMG, there is prominent muscle membrane irritability characterized by fibrillation, positive waves, and even myotonic discharges. These are particularly noted in proximal muscles. The motor unit action potentials are polyphasic, small, and short, and have early recruitment.

CRDs are bursts of spontaneous EMG activity that repeat at a regular frequency which typically has an abrupt beginning and end. They are non-specific but can be a sign of either neuropathic or myopathic processes.

Audibly, they can be compared to a running motor.

This is an EMG of the right tibialis anterior muscle. Notice the reduced recruitment. There is also polyphasic and prolonged duration of MUAPs. This is consistent with chronic denervation.

This EMG showcases changes that are consistent with a chronic radial mononeuropathy. Appreciate the decreased recruitment of MUAPs with activation.