'Adductor spasmodic dysphonia' (SD) is a focal laryngeal dystonia mainly resulting in a strained voice quality with spastic voice breaks and frequency shifts, perturbing fluency and intelligibility. It is well known that SD-patients report unusually high scores on the YHI, as they experience their disease as seriously impairing their quality of life. The standard treatment is Botulinum Toxin (BT) injection in the thyroarytenoid muscles, in order to interfere with the perturbed sensory feedback loop of kinetic muscle tension regulation. The mode of action of this toxin is at cholinergic nerve terminals where it inhibits the release of acetylcholine. However, the globally favourable effects are only temporary, in part because of the formation of remodeled neuromuscular junctions after a few months, but the Botulinum injections can be repeated. There is a lack of information about long term effects.