Movement disorders

Parkinson’s syndrome was first described by James Parkinson in 1817. The principal pathological disorder is a depletion of dopamine stores in the cells of the substantia nigra and neostriatum. This produces the classical triad of tremor, rigidity and akinesia. As early as 1820, Parkinson appreciated that stroke ablated contralateral tremor. Over the next century, neurosurgeons lesioned various parts of the central nervous system in an attempt to alleviate this tremor until it was thought that the surgical relief of tremor boiled down to the artificial production of paralysis. The development of stereotactic techniques and a better understanding of the circuitry of the basal ganglia led to the development of the thalamotomy procedure. By 1975, 75 000 thalarnotomies had been performed world-wide. However, in 1969, the discovery of levodopa led to the cessation of surgery for Parkinson’s disease. The subsequent development of on—off phenomena, dyskinesias and dystonias in patients treated with doparnine led to a revival of interest in movement disorder surgery. New imaging techniques and work on animal models of Parkinson’s disease led to the discovery of new targets in the basal ganglia and the procedure as we know it today.

Thalamotomy is used to treat patients with drug-resistant tremor but does little to improve akinesia and rigidity, and has an inconsistent effect on levodopa-induced dyskinesias. Case series have demonstrated that pallidotomy is helpful in reducing levodopa-induced dyskinesias. Underlying parkinsonism also improves but to a lesser degree. Unilateral procedures are usually preferred to bilateral ones as some centres have reported an increase in the risk of complications with the latter such as speech impairment and neuropsychological impairment (Fig. 35.45). More recently, the subthalamic nucleus has been lesioned, alleviating akinesia in addition to tremor and rigidity. This target does however expose patients to a higher risk of haemorrhage.

Lesions are made either by radiofrequency coagulation after trial stimulation or by deep brain stimulation of any of the sites targeted for lesioning. Although stimulators do not require tissue destruction, they are expensive and prone to technical failures. They can however be turned on and off, programmed as necessary and are reversible.

Neural transplantation of foetal mesencephalon to the neostriatum of humans is a controversial experimental tech­nique which has had variable and questionable success. In addition, the ethics of obtaining foetal tissue and the problems of immunological reactions have led to the call for a moritorium on this procedure until long-term results are available.