Electromyography Flashcards
What is electromyography (EMG)?`What does it evaluate?
recording and study of insertional, spontaneous, and voluntary electrical activity of muscle. Evaluate the motor unit, incl. anterior horn, peripheral nerve, and muscle.helps for evaluation of muscle weakness
How is EMG performed?
insertion of a needle electrode into the muscle in question. Evaluate the compound motor action potentials visually and aurally.
What are the 2 types of electrodes used for EMG studies?
monopolar electrodes and concentric electrodes
What do monopolar electrodes do?
record the potential between the electrode and a ground electrode palced some distance from the electrode. can cover a large recording area and is somewhat less uncomfortable than concentric electrodes.
What do concentric electrodes do?
record the potential btw the bare tip and the shaft of the electrode. limited recording area and are more uncomfortable.
What 4 parameters are studied in an EMG?
insertional activity, spontaneous activity, voluntary activity, and recruitment pattern
What is insertional activity on an EMG?
electrical response of muscle to mechanical damage of needle movement. electrical activity recorded within the first second of needle insertion. typically brief (.5-1 s) but may be long in acute neuropathies and active myopathies.
What is spontaneous activity on an EMG?
AP recorded from a muscle at rest after insertional activity has subsided and when there is no voluntary contraction. Spontaneous activity may be normal or abnormal.
What is Normal spontaneous activity on an EMG?
miniature end plate potentials that occur regularly at the NMJ due to spontaneous release of ACh quanta
What are 5 forms of abnormal spontaneous activity seen on an EMG?
fibrillations positive sharp waves fasciculations, myotonic discharge complex repetitive discharges
What are fibrillations?
activity from fibrillating muscle fibers: AP from a SINGLE MUSCLE FIBER. Occur repetitively and regularly. biphasic spikes of short duration with an initial positive phase and an amplitude less than one millivolt.
What are positive sharp waves?
biphasic, positive-negative APs associated with fibrillating muscle fibers and representing this discharge of a single muscle fiber.
What is the clinical significance of fibrillations or positive sharp waves?
same significance
positive sharp waves seen when the electrode is recording from an area of damaged muscle
fibrillations and positive sharp waves both seen with acutely denervated muscles or with active inflammatory myopathies
What is fasciculation?
fasciculation is a sporadic, spontaneous AP of a SINGLE MOTOR UNIT associated with clinical fasiculation
What is the potential clinical significance of fasciculations?
usually occur as a result of discharge from an anterior horn cell or a peripheral nerve. occasional fasciculations associated with fatigue are normal. continuousm widespread fasciculations are associated with anterior horn cell disease like ALS
What is myotonic discharge?
Repetitive discharge of biphasic spike potentials recorded after needle insertion or after muscle percussion in which the amplitude and freq of the potentials wax and wane. makes a sound like a dive bomber.
What is the clinical significance of myotonic discharge?
often a problem with channels, as is seen in myotonic dystrophy and congenital myotonia.
What is complex repetitive discharge?
polyphasic AP that may begin spontaneously or after needle movement. Uniform frequency, shape, and amplitude, as well as abrupt onselt, cessation, or change in config. Nonspecific: may be seen in neuropathic or myopathic disease.
What is the voluntary activity parameter of EMG?
electrical activity recorded from a muscle with consciously controlled muscle contraction.usually consists of compound muscle APs (sum of the APs of all fibers innervated by a single anterior horn cell).
How are motor unit potentials evaluated in an EMG for voluntary activity (what parameters)
amplitude, duration, presence or absence of polyphasia (5 or more crossings of baseline)
For voluntary activity, what is meant by duration and amplitude?
amplitude: lowest pt to highest pt
duration: baseline to baseline
