Scott Adams said he had it as well and that there is an operation that can fix it, which he had done, but they've made it hard to find and harder to get.

Ah. I had no idea it was a neurological disorder. I feel bad now for asking and hope he can continue being an advocate for it.

Is the Cause of Spasmodic Dysphonia Known?

Spasmodic dysphonia is known to be neurological in origin, but currently, the exact cause is not known. Investigation into the specific causes of the disorder is ongoing, and different areas of the brain may be involved. Researchers are looking at the basal ganglia, which helps to regulate movement; the cerebellum, which helps to control balance; along with the cortex which initiates movement and senses sensation. There may also be genetic component [Note RFK's sister is developing it also] as genes have been identified in other forms of dystonia.

https://www.youtube.com/watch?v=CC66Mh7C2nA

he claims it was caused by a parasitic worm.