Electrotherapy diagnostics online multiple choice questions and answers-7
- Electrodiagnostic findings common in myopathies include:
A) Low amplitude sensory nerve action potentials (SNAP)
B) Long duration motor units
C) Abnormal spontaneous potentials (denervation) on needle electromyography (EMG)
D) Increased firing frequency of motor units - Monopolar needles generally have higher amplitude motor unit action potentials (MUAPs) than concentric needles because:
A) Monopolar needles are longer than concentric needles
B) The needle samples from 360° rather than 180°
C) The tip of a concentric needle is smaller
D) Concentric needles have the ground electrode as part of the needle - On needle electromyography (EMG), normal motor units have a duration of:
A) 20 to 30 msec
B) 5 to 15 mcsec
C) 20 to 30 mcsec
D) 5 to 15 msec - A motor point is:
A) The thickest part of the muscle
B) The tip of the needle
C) The point where the nerve enters the muscle
D) Not seen in all muscles - In nerve conduction studies, temporal dispersion is a result of:
A) A large variance in conduction velocities in the fibers that make up the compound motor action potential (CMAP)
B) Slowed conduction velocity in all fibers
C) Axonal loss
D) Different velocities in different segments of the nerve - While performing a needle electromyography (EMG) study, the reference electrode (G2) is placed:
A) Distally over an electrically neutral area (tendon or bone)
B) Proximally over an electrically neutral area (tendon or bone)
C) Distally over a muscle
D) Over the same muscle that the needle is in - The sensory continuation of the femoral nerve is the:
A) Lateral femoral cutaneous nerve
B) Obturator nerve
C) Sural nerve
D) Saphenous nerve - Which muscle is innervated by the sciatic nerve?
A) Tensor fascia lata
B) Iliopsoas
C) Gracilis
D) Adductor magnus - The classic finding on electrodiagnostic testing in a patient with diabetic neuropathy indicates what type of polyneuropathy?
A) Axonal motor polyneuropathy
B) Uniform-demyelinating mixed sensorimotor polyneuropathy
C) Segmental-demyelinating motor polyneuropathy
D) Mixed axonal demyelinating sensorimotor polyneuropathy - Limitations of the H-reflex include all the following except:
A) Abnormal H-reflex is not truly indicative of radiculopathy, as the lesion may involve other parts of the long pathway (such as the plexus or spinal cord)
B) H-reflex is often absent in otherwise normal individuals older than 60 years
C) Patients with an S1 radiculopathy can have a normal H-reflex
D) All of the above are limitations
Electrotherapy diagnostics online multiple choice questions and answers-7 Answer Online Multiple choice Question
- C) Denervation can be found in neuropathic or myopathic processes. As myopathies only affect the muscle, SNAPs should be preserved. The motor units are usually short-duration, small amplitude, polyphasic potentials with early recruitment.
- B) Concentric needles are beveled and therefore only pick up from 180° around the needle tip. Monopolar needles pick up electrical activity from 360°. Therefore, the MUAP amplitudes from a monopolar needle are usually larger than those from a concentric needle. It is important to include information about the type of needle in the report so that the amplitude can be interpreted correctly. Concentric needles have the reference electrode as part of the needle and require a separate ground.
- D) Duration is the time from the initial baseline departure to the final return to baseline. Normal duration is about 5 to 15 msec or approximately one horizontal division with a commonly used sweep speed of 10 msec/division. It represents the degree of synchrony in the fi ring of the individual motor fibers that contribute to the motor unit. With reinnervation, there is asynchrony of fi ring of individual muscle fibers due to immature myelin. Therefore, duration of a motor unit increases with reinnervation and can be seen in chronic neuropathic processes. Decreased duration may be seen in myopathic disorders.
- C) The motor point is the area where the nerve enters the muscle. This is usually located near the middle of the muscle belly. It is also known as the end-plate zone.
- A) When many of the fibers that make up the CMAP have different velocities, the resulting waveform will be more dispersed. Remember that the latency reflects the fastest fibers. Those at the end of the CMAP reflect the slowest fibers. Even though this slowing is a result of a demyelinating lesion, the CMAP amplitude may be decreased with temporal dispersion. Again, this is because there is a wider variation of conduction velocities and the CMAP has a longer duration. However, the area under the CMAP curve will be the same. Therefore, if a decreased amplitude is noted, do not automatically assume it is due to an axonal lesion. Assess the duration of the waveform. If it is prolonged, the decreased amplitude may be due to dispersion.
- D) Placing the surface reference electrode over the same muscle that the needle is in will decrease the baseline noise. The EMG machine will “subtract” the electrical signal of the reference from the active electrode signal. Therefore, any surface “noise” will be eliminated.
- D) The saphenous nerve is the sensory continuation of the femoral nerve. It supplies sensation to the medial leg and foot.
- D) The adductor magnus is innervated by both the obturator and the sciatic nerves. The superior gluteal nerve innervates the tensor fascialata, the femoral nerve innervates the iliopsoas, and the obturator nerve innervates the gracilis.
- D) Diabetes (along with uremia) usually involves both the axon and the myelin with fi ndings in motor and sensory fibers. Conditions associated with axonal motor polyneuropathy include porphyria and axonal type Guillain-Barré syndrome. Hereditary neuropathies usually present with uniform-demyelinating mixed sensorimotor polyneuropathy. Conditions that may present with segmental-demyelinating motor polyneuropathy include Guillain-Barré syndrome (acute inflammatory demyelinating polyneuropathy) and hypothyroidism.
- D) All the choices are valid limitations of the clinical utility of the H-reflex. As this reflex assesses a long neural pathway (including the orthodromic Ia afferents, the dorsal root ganglion to the spinal cord, interneurons, and then orthodromically to the muscle), a delay may not be specific to a radiculopathy. The lesion can be anywhere along the pathway.
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