LCA-Only Paresis

LCA-only paresis refers to weakness or paralysis of the vocal cord’s lateral cricoarytenoid (LCA) muscle, but with normal function of the vocal cord’s other muscles. The LCA muscle helps to bring the vocal cord to the midline for voice production and, more specifically, to bring the “toe” of the arytenoid cartilage to the midline.

The following are indicators of LCA-only paresis:

Movement: The vocal cord opens normally for breathing. From a distance, it can appear to close normally for voicing, but more acute and up-close inspection often shows a faint lag or reduction of crispness of approach to the midline, and inspection of the posterior commissure at close range shows that in fact it does not fully adduct.
Position and appearance: Position is normal during breathing, but again, the vocal cord does not come fully to the midline for voicing. A tell-tale indicator of LCA-only paresis is lateral turning of the vocal process. This lateral turning is seen best in low voice, and is a little less apparent with very high voice (as illustrated by a pair of photos below).
Appearance during voicing (under strobe lighting): Persistent slight gap between the vocal cords posteriorly, with the laterally turned vocal process, but no flaccidity of the cord with vibration. Normal tone and bulk of the vocal cord itself.
Voice quality: Weak and air-wasting, but without the luffing and diplophonia often apparent when the thyroartyenoid (TA) muscle is also paralyzed.

Evolution of Vocal Cord Paralysis To End as PCA-only Paresis

For some voice doctors, measurement is accorded more respect than observation. Both are legitimate, of course, yet, visual (observational) understanding of paralysis and paresis remains far more useful than EMG, acoustic, or aerodynamic measurements. This case strongly illustrates that point.

This older man underwent thoracic surgery but due to complications was also intubated for much of two days. Immediately upon awakening, his voice was altered. He said it was whisper only.

At his original office visit a month later, he thought his voice had improved to “10%” and examination showed left vocal cord paralysis (TA, LCA, and PCA muscles all non-functional). Three months later, his voice was by his description to 40% and improving further week by week. By month 8 post-surgery, verified at 18 months, he felt his voice was “99%” recovered; examination showed recovery of TA and LCA, but not PCA muscle.

The final diagnosis: Left PCA-only paresis. Rather than being entirely “out,” the PCA seems only to be weak.

Left Cord Margin Bowing (TA weakness) (1 of 11)

A month after thoracic surgery that took voice from “100%” preop to “0” postop (whisper only). Breathing position (partially open) shows bowing of the left cord margin (right of photo).

LCA Paresis Also... — LCA Paresis Identified (2 of 11)

Just before vibration (phonation) begins, there is a large gap between the cords. The left TA-related bowing/atrophy remains obvious, and the tip of the vocal process (VP) is turned laterally, indicating weakness of the left LCA muscle.

Breathy voice — Voice is Breathy! (3 of 11)

Now creating an exceedingly breathy voice (see vibratory blur) with a phonation time of mere seconds due to air wasting between the cords. Two critical muscles for producing voice, TA and LCA, are not working.

The key photo showing weakness of the LCA muscle with lateral turning of the left vocal process — LCA Paresis Best View (4 of 11)

The key view is during voicing when LCA weakness is appreciated by noting lateral turning of the left vocal process (circled arrow).

At 4 months, TA bowing but is LCA working a little? — 4 Months Later, Glottis Open For Breathing (5 of 11)

Now at 4 months post-injury, this view is rotated; the left cord (right of photo is lateralized and the left (bowed) cord is actually midline. Is slight medial turning of the vocal process (VP) imaginary? That would correlate with the patient’s comment that voice is noticeably better and continuing to improve week by week.

Gap during phonation is less; slight recovery of LCA — Gap during phonation Less (6 of 11)

During phonation, the gap between the cords is less than in Photo 4, and lateral turning of the left vocal process (arrow) less exaggerated. This suggests slight recovery of the left LCA muscle.

Main deficit that remains is PCA weakness seen as lack of lateralization — PCA Weakness Is All That remains (7 of 11)

At 8 months from the injury, the patient says his voice is completely recovered. In this breathing position, one can see that the left PCA muscle which should lateralize that cord is still not working, explaining the midline position of the left cord (right of photo). But of course, the PCA muscle deficit does not affect voice, but only the size of the glottic aperture during breathing…But tone in the LCA muscle is clearly turning the vocal process medially.

Tips of vocal process turn medially on both sides now — LCA Recovered: The Vocal Process Now Turns Medially (8 of 11)

Both vocal process turn medially for phonation, suggesting recovery of the left LCA muscle, even though the right vocal process rides up on top of the left (seen not infrequentlyin older larynges).

At 18M, Left Cord Does Not Abduct Due To Continuing PCA Weakness (9 of 11)

At 18 months, and continuing to feel his voice is normal. In this breathing position, the glottic aperture is reduced because the left cord does not lateralize, consistent with ongoing weakness of the left PCA muscle. The bowing is not significant because PCA weakness coupled with normal TA and LCA create bowing while breathing, even in young people. See also the next photo.

Bowing abolished — Left PCA Can Muster Some Lateralization (10 of 11)

When the patient sniffs, his weak left PCA muscle does lateralize the cord, somewhat, abolishing the “bowing” seen in photo 9.

Healed Paresis — Full Recovery for Voicing, Despite PCA-Only Paresis (11 of 11)

At the prephonatory instant, both vocal processes come into straight-line contact (compare with photos 4 and 6. Keep in mind that PCA weakness alone does not affect voice but PCA-only paresis is seen only during breathing, as in Photo 10.

LCA Weakness

Lateral cricoarytenoid (LCA) weakness is best seen during phonation. Lateral turning of the vocal process during voicing is the “key” finding, though there are others. We say the “toe” (tip of vocal process) is turned laterally. The “heel” of the arytenoid is together, signifying normal function of the interarytenoid (IA) muscle.