Voice change that accompanies Parkinson’s disease (PD) typically has two components. One component is a change to the “inner engine” of the voice. It is as if the inner motivation or vitality of communication or voice is damped down; think of the “motor” being limited mostly to “idle” rather than “first, second, third, and fourth” gears. When coaxed or even goaded to produce more vigorous voice, a person with advanced PD may find it hard to impossible (depending upon severity) to increase loudness. If the average person can “choose” vocal loudness settings of 1 through 5, it is as though levels 2 through 5 become inaccessible to the person with PD.
A second component of PD-related voice change is that the larynx becomes weak and atrophied. This is not surprising, since any body part will tend to atrophy if it is never used in a vigorous way. The phenomenology of PD-related voice change is that the voice is overly quiet and soft-edged, and though speech does not tend to become slurred, it can lose its crispness of articulation, and the pace of speech may diminish.
Parkinson’s-related voice change (1 of 3)
Larynx of person with severe Parkinson’s disease; breathing position. Note the remarkable atrophy of the vocal cords, manifested in particular by the capacious ventricles (green dotted lines), the margin bowing (arrows), loss of “conus” bulk, and increased visibility of the contours of the vocal processes (blue dotted lines).
Parkinson’s-related voice change (2 of 3)
Phonatory (voicing) position. In addition to the bowing of the vocal cords, especially the left cord (right of image), note the slight scissoring of the left vocal process to overlap the right vocal process, as indicated by the arrows.
Parkinson’s-related voice change (3 of 3)
Cords coming into phonatory position, magnified view. Here can be seen even more clearly that, due to Parkinson’s-related atrophy, the contours of the vocal processes are more visible (blue dotted lines), like an emaciated person’s ribs. Note also that the LCA muscles have contracted slightly before the IA: the “toes” (T’s) of the arytenoid cartilages are in contact before the “heels” (H’s).