HSC Section 6 Nov2016 Green Book

to support the diagnosis alone. Only one respondent rou- tinely relied on LEMG for diagnosis, and only the minor- ity of patients ever had LEMG at all. Many reasons may prevent the use of LEMG, lack of availability and exper- tise prominent among them, but respondents felt that the sensitivity of LEMG was not high. There is little doubt that LEMG is highly specific for neuropathy. Find- ings of fibrillations, positive sharp waves, or polyphasic motor unit action potentials are unambiguous signs of neurologic impairment. Unfortunately in paresis, such clearly abnormal findings may be absent or obscured. Decreased recruitment of otherwise normal-appearing motor unit action potentials may be the only abnormality present. Because this relative change may be small and mimicked by incomplete muscle activation or suboptimal needle placement, there remains a role for physician judgment and inevitably error. Moreover, the maximal interference pattern in striated muscle is typically pres- ent at only 30% of maximum isometric contraction, which creates the possibility that even substantial paresis may be obscured during testing. Thus, although LEMG can provide important information that laryngoscopy cannot, it is not clear that it is a more accurate diagnostic tool than laryngoscopy in the diagnosis of VFP. Reliance on laryngoscopy begs the question of which findings are considered important. To say that one may find signs of paresis in virtually every larynx is only a mild exaggeration. Unlike systems such as the extraocu- lar muscles, mild discoordination in the larynx probably carries little functional and evolutionary disadvantage as long as glottic closure for airway protection is brisk and effective. Thus, much asymmetry in vocal fold

TABLE II. Practice Related to VFP

49 6 3.2, r 5 25

New patients with voice-related complaint/month

8.5 6 1.6, r 5 12

VFP diagnosis/month

Diagnosis of VFP Rests Principally On: History

1 (1.7%)

Laryngoscopy (continuous light)

10 (17%) 42 (72%)

Strobovideolaryngoscopy

LEMG

1 (1.7%)

96 6 1.6%, r 5 12

% Patients diagnosed with VFP who had videostroboscopy % patients diagnosed with VFP who had LEMG

26 6 4.0%, r 5 31

LEMG 5 laryngeal electromyography; VFP 5 vocal fold paresis.

represent paresis or paralysis in large part) in 346 (83%) patients. Sataloff et al. 14 reviewed 751 patients who underwent LEMG for all causes over a 4-year period. This series contained 689 suspected cases of paresis/ paralysis by videostrobscopy, with LEMG confirming the diagnosis in 661 patients (95.9%). The variation among these three series reveals substantial differences among practitioners regarding diagnosis and testing. Respondents indicated that they principally relied on laryngoscopy, usually under stroboscopic light, to make the diagnosis of VFP. Although LEMG is the only way to definitively diagnose laryngeal neuropathy objec- tively in vivo, the vast majority of respondents evidently felt that laryngoscopic criteria were sufficiently reliable

Fig. 4. Positive predictive value of laryngoscopic signs for vocal fold paresis. MW 5 mucosal wave; VF 5 vocal fold.

Laryngoscope 125: April 2015

Wu and Sulica: Paresis Survey

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