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 in 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 is common, affecting 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. Each of these structures consists of two parts: one on the left hand side of the brain and one on the right. Surgery may be carried out on one or both sides.
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, through either destruction or electrical stimulation, the function of brain nuclei – such as the thalamus, globus pallidus or subthalamus – that interact functionally with the substantia nigra. Deep brain stimulation is one form of surgery for Parkinson's disease.
2.2.1 This procedure involves inserting very fine needles into the brain through small holes made in the skull to determine the exact position of the nucleus to be stimulated, which may be different in each patient. This part of the procedure is usually carried out under local anaesthetic. Once the nucleus is identified, a permanent electrode is placed into it. Under general anaesthetic, this electrode is then connected to a pulse generator, which is implanted subcutaneously on the anterior chest wall.
2.3.1 The evidence suggested that deep brain stimulation results in improved motor skills, function and movement in patients with Parkinson's disease. For more details refer to 'Sources of evidence'.
2.3.2 The Specialist Advisors considered the procedure to be established practice within specialised units. They did not question short-term efficacy, but commented that long-term efficacy was unknown. One Specialist Advisor commented that careful selection of patients was crucial to maximise the chances of success of the procedure.
2.4.1 The complications associated with deep brain stimulation include risk of stroke, confusion, speech disorders and visual problems. In the two largest studies, involving 102 and 111 patients, the incidence of stroke was approximately 3%. For more details refer to 'Sources of evidence'.
2.4.2 The Specialist Advisors noted that all procedures involving deep brain stimulation carried similar risks. They considered the procedure to be safe if performed by a multidisciplinary team in a neuroscience unit. The team should include a neurologist and a neurosurgeon, and the unit should have facilities for psychological assessment and, ideally, neurophysiology.