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.