Fig. 5.7. Many motor units firing slowly indicating concern for a central deficit. Note that the recruitment pattern is not as full as in Fig. 5.5, and that the motor units do not seem to be rapidly repetitive as in Fig. 5.5. This condition is characterized as "many motor units firing slowly."
2. A severe peripheral nerve injury with a few motor units, usually firing fast
3. A moderate peripheral nerve injury with many motor units but decreased recruitment
These four groups can further be characterized by the types of motor units present and the timing of their activity associated with phonation. If polyphasic potentials are present, it is important to consider that ongoing recovery is occurring and that a delay in definitive treatment might be indicated. If large-amplitude motor units are present, the examiner can have some confidence that the recovery has matured and is stable. When examining the timing of responses, synkinesis can be diagnosed if the PCA is active with simple phonation, or the TA/LCA is more active with a sniff than during voice tasks ,
Unilateral vocal fold immobility is frequently managed without LEMG. Therapeutic choices among voice therapy, vocal fold medialization, arytenoid repositioning procedures, injection medialization, and reinnervation are based on the visual exam and physician preference; however, decisions are made and outcomes are assessed without a clear understanding of the underlying injury.
The LEMG provides information about the pathophysiology of vocal fold immobility and dysmotility. With this information, the physician can make therapeutic choices based on an understanding of the etiology of the disorder [17, 21, 31]. In the previous section, an example of suspected arytenoid dislocation was discussed. Rather than proceed to a general anesthetic and attempted operative intervention, the physician can observe the patient if an LEMG demonstrates paralysis. In the case of immobility due to cricoarytenoid joint fixation, a normal LEMG would deter one from performing a reinnervation procedure that would likely worsen the voice. In the case of dense paralysis, the physician might be directed toward a reinnervation.
A lack of understanding of the pathophysiology of vocal fold movement has led to the reporting of widely varying reports of success
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