Muscle Weakness Evaluation to Management

Electrodiagnostic studies are used to elucidate abnormal neuromuscular transmission and to exclude other diseases of the motor unit that may mimic or contribute to the clinical findings. Electromyographic studies may also be useful in measuring the severity of involvement and demonstrating changes as the disease develops. Although the detailed account of available electrodiagnostic techniques would take several volumes, certain generalities are worth remembering, as they may affect both the diagnostic and treatment modalities appropriate for patients who, due to the nature of their employment (e.g., seasonal workers) may not benefit from the longer observation times often required in slow developing conditions.

The most commonly used electrodiagnostic test of neuromuscular transmission involves repetitive stimulation of a motor nerve while recording compound muscle action potentials (CMAP) from a muscle innervated by that

Table 17.3. Assessing the patient's fitness to drive or operate machinery.


Red flag answer

Is patient's alertness adequate? Is patient's vision adequate? Is patient's reaction adequate?

Is the patient's movement adequate? Is the patient's cognition adequate?

Is the patient's vigilance and fine motor control adequate?

"Inadequate" or "slow" "Fails to see (sides, blind spots, etc.)" "Slow to react" or "Reacts too fast and incorrectly (e.g., begins to move when the left turn arrow lights up at a complex intersection even though there is red light for his/her lane)" "Fails to work levers, gears etc." "Drives in one gear" "Fails to get to destination" "Forgets known routes, avoids unfamiliar routes etc." "Can't drive and talk at the same time" "Swerves when changing radio settings"

Source: Data from Meyers et al. (27), Zesiewicz et al. (29), and Rau (30).

nerve. The result is abnormal if progressively fewer muscle fibers respond to nerve stimulation during a train of stimuli, producing a "decrementing" pattern in the CMAP (35).

Weakness from abnormal neuromuscular transmission improves after intravenous administration of 10 mg (in fractional doses) edrophonium chloride (Tensilon). For a Tensilon test to be considered positive, a dramatic, unequivocal improvement in muscle function should be observed directly by the examiner. Increasing weakness after administration of these doses of Tensilon (a paradoxical response) is also an indication that neuromuscular transmission is impaired. This test carries significant risks of adverse effects (respiratory and circulatory) and should not be viewed as "first line" (36).

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