Weakness or paralysis of the vocal cord’s thyroarytenoid (TA) muscle, but with normal function of the vocal cord’s other muscles. The TA muscle “inhabits” the vocal cord and normally provides bulk and internal tone to the cord. The following are indicators of TA-only paresis:
- Movement: The vocal cord opens normally for breathing and closes normally for voicing.
- Position and appearance: Position is normal. Typically, the margin of the cord is slightly concave, the ventricle is capacious, and the conus area below the free margin is lacking in bulk.
- Appearance during voicing (under strobe lighting): Closure at the posterior commissure is complete and symmetrical bilaterally. Under strobe light, one sees flaccidity as indicated by increased amplitude of vibration; the lateral excursions become exaggerated and the mucosal wave increases. One may also see chaotic fluttering.
- Voice quality: Weak and air-wasting and often indistinguishable from a case of complete vocal cord paralysis—TA, LCA (lateral cricoarytenoid), and PCA (posterior cricoarytenoid).