Surgery is resorted to only when drug therapy fails. Possible procedures include everything from implanting devices and transplanting neural tissue to blasting the troublesome brain cells with an electrode - all with limited success and major side-effects.

The most successful of these is deep brain stimulation, where a device that emits an electrical current is implanted in the brain and supplied by an external pacer (rather like a heart pacemaker). The device can be turned on or off by the patient via a hand-held magnet.

One study showed that the majority of PD patients experienced an 82-per-cent reduction in tremor and significant improvements in tasks such as writing and pouring drinks following implantation (Neurology, 1998; 51: 1063-9). Among the few reports of the long-term effects of DBS, one study reported significant suppression of severe tremor over a six-year follow-up period (Mov Disord, 2003; 18: 163-70).

However, another long-term study of 25 patients found that DBS stops working in some cases. Also, three patients showed haemorrhages within the brain, but with no clinical symptoms, and one patient developed postoperative seizures. In addition, complications with the devices increase the risk of additional surgery (Mov Disord, 2001; 16: 464-8).

Nevertheless, in general, the treatment improves the quality of life for PD patients and their caregivers, and enables a reduction in drugs, such as levodopa (Neurologia, 2003; 18: 187-95), which are known to have adverse side-effects when used for extended periods of time (see box, p 3).