>Spasmodic dysphonia (SD) is a disorder in which the muscles in the voice box that move the vocal cords are abnormal.
It causes spasms when the sufferer tries to speak, causing the voice to break or to have a strained or strangled quality.
Dr Thomas Loh, the chief of the department of otolaryngo- logy, head and neck surgery at the National University Hospital, said: 'Typically the patient is well at rest. But during speech, he has a choked voice, stop-starting and using short sentences. There is an abrupt ending to sentences. The voice may be hoarse or breathy.'
Surprisingly, the spasms are usually absent while whispering, laughing, singing, speaking at a high pitch or speaking while breathing in.
Stress, however, often makes the muscle spasms more severe.
SD can affect anyone, although more women appear to be affected than men.
Its cause is unknown.
Because the voice can sound normal at times, SD was once thought to be psychological. But increasingly, research is linking it to the nervous system.
An otolaryngologist - ear, nose and throat (ENT) specialist - a speech/language specialist and a neurologist work in tandem to diagnose SD.
The ENT doctor threads a lit tube through the nose into the throat to evaluate vocal cord movement during speech. The speech/language specialist evaluates voice quality. The neurologist looks for signs of other muscle disorders.
There is no cure for SD but botox injections into the vocal muscles give almost immediate relief. The effect lasts about four months, so a patient may require repeated injections.