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.