2 The procedure
2.1.1 Parkinson's disease is a chronic disease of the brain characterised by gradually worsening tremor, muscle rigidity, and difficulties with starting and stopping movements. The condition is usually treated with drugs. Surgery may be considered for people who have responded poorly to drugs, who have severe side effects from medication or who have severe fluctuations in response to drugs (on–off syndrome).
2.1.2 Parkinson's disease affects about 0.5% of people aged 65 to 74 years and 1–2% of people aged 75 years and older. Experts believe that 1–10% of people with Parkinson's disease might be suitable for brain surgery.
2.1.3 Surgery for Parkinson's disease is carried out on structures within the brain that are responsible for the modification of movements, such as the thalamus, the globus pallidus and the subthalamic nucleus. Surgery may be carried out on these structures in either or both hemispheres of the brain.
2.1.4 Surgical treatment aims to correct the imbalance created by diminished function of the substantia nigra – the underlying abnormality in Parkinson's disease. Surgery alters, either through destruction or electrical stimulation, the function of brain nuclei (such as the thalamus, globus pallidus or subthalamus) that interact functionally with the substantia nigra. Subthalamotomy is oneform of surgery for Parkinson's disease.
2.2.1 Subthalamotomy involves inserting very fine needles into the brain through small holes made in the skull, to destroy a part of the subthalamic nucleus using heat or radiofrequency. The exact points of needle insertion may be different in each patient. The procedure is usually carried out under local anaesthetic. Patients remain awake during the procedure so that the effects on movements can be monitored.
2.3.1 The evidence was limited to small case series, with only two case series assessing efficacy on a total of 32 patients. Both these studies suggested an improvement in motor skills as measured by the Unified Parkinson Disease Rating Scale (UPDRS) at 12 months' follow-up. For more details, refer to the Sources of evidence.
2.3.2 The Specialist Advisors commented that there were not enough data to assess the long-term benefits of subthalamotomy for Parkinson's disease, and that subthalamic electrical stimulation had become the preferred intervention.
2.4.1 Reported complications included persistent dyskinesia, deterioration in learning and retrieval, and deterioration in spatial working memory. In one study of 66 patients, signs of cerebellar dysfunction persisted in 41% (27/66) of patients 2 weeks after surgery. For more details, refer to the Sources of evidence.
2.4.2 The Specialist Advisors listed the potential complications as risk of stroke; hemiballismus; and disturbance of speech, swallowing or gait. One Advisor was concerned about the irreversible nature of subthalamotomy and the potential need for repeated surgery.