A documentary on Channel Five yesterday evening followed a surgeon as he used deep brain stimulation to treat two patients with severe cases of Tourette’s Syndrome.
Tourette’s is a relatively rare neuropsychiatric condition, affecting up to 1 in 100 people. It is most frequent among Ashkenazi Jews and people of Mediterranean extraction, with boys being affected three times more than girls. Onset normally occurs between 7-10 years of age. The condition is a motor disorder, characterized primarily by a lack of muscle coordination, which leads to involuntary movements called tics. These are often associated with self-injurous behaviour. Some patients with Tourette’s also exhibit vocal tics; this symptom, called coprolalia, leads to frequent and involuntary swearing. Occasionally, this is accompanied by copropraxia (the production of obscene gestures), coprographia (producing obscene drawings) and echolalia (repeating the things that others say). Often these symptoms are only exhibited when the patient is in the presence of other people.
Diagnosis of Tourette’s can be very difficult, because there are a wide variety of symptoms which can differ hugely in their severity. Tourette’s is therefore often placed within a spectrum of tic disorders Another reason that diagnosis is difficult is that patients with Tourette’s often also have other disorders; attention-deficit hyperactivity disorder (ADHD) and obsessive-compulsive disorder (OCD) are most common, but Tourette’s patients can also present with anxiety, depression and emotional and social difficulties. Further- more, the symptoms of Tourette’s can wax and wane over time. Therefore, children who exhibit mild tics are not diagnosed as having Tourette’s unless their symptoms persist for more than a year.
The behaviour of people afflicted with the condition can make Tourette’s socially debilitating. This is clear from the following film clip of John Davidson, who has a severe case of the condition:
WARNING: THIS CLIP CONTAINS EXTREMELY STRONG LANGUAGE
Tourette’s Syndrome is named after the French neurologist Georges Albert Édouard Brutus Gilles de la Tourette, who first described the condition in an 1885 paper in the journal Archives de Neurologies, called Étude sur une affection nerveuse caractérisée par de l’incoordination motrice accompagnée d’echolalie et de coprolalie (Study of a nervous affliction characterised by motor incoordin- ation accompanied by echolalia and coprolalia). In that paper, Gilles de la Tourette described nine patients who had what he called “maladie des tics”; one of these patients was Marquise de Dampierre, a French aristocrat who “ticked and blasphemed”, from the age of 7 until her death at the age of 80. Charcot later referred to it as Gilles de la Tourette’s illness, and this is proper name of the condition.
Both environmental and genetic factors are known to play a role in Tourette’s syndrome. A number of loci, on different chromo- somes, have been implicated in the condition. Some geneticists now believe that Tourette’s is a result of the concerted actions of a number of genes, but a difficulty here is that some of these genes have a dominant, others a recessive, and yet others an inter- mediate inheritance. Environmental factors are also known to be involved: monozygotic (identical) twins share the condition in about 80% of cases, and, even in these cases, there can be marked differences in symptoms.
Recent neuroimaging studies have implicated the basal ganglia in Tourette’s. These are a set of interconnected structures lying underneath the cerebral cortex, which are involved in the control of movement. The basal ganglia send projections to the cerebral cortex and thalamus, which in turn contain neurons that project back to the basal ganglia. One component of the basal ganglia, the substantia nigra, degenerates in Parkinson’s Disease, another motor disorder characterized by involuntary movements. The feeback loop between the cortex and the basal ganglia is involved in integrating brain function. The basal ganglia relays information from command centres in the cortex to the peripheral nerves and muscles which execute those commands, and it is thought that dis- inhibition of basal ganglia circuitry is the cause of the involuntary movements seen in Tourette’s, Parkinson’s and other motor disorders.
For about 40 years, Tourette’s has, like Parkinson’s Disease, been treated with drugs which alter the dopaminergic transmission in the basal ganglia. The use of deep brain stimulation to treat the condition has only been attempted a small number of times. The tech- nique involves the implantation of battery-powered electrodes into the medial region of the thalamus, which is part of the circuit linking the basal ganglia and cortex. Once in place, high frequency electrical stimulation of the thalamus by the device interferes with the signals producing symptoms.
In the few Tourette’s patients in which the technique has been used, there was a significant improvement, with an almost complete cessation of tics and, sometimes, of coprolalia. The method is, however, still in the experimental stages. It has not yet been deter- mined which part of the thalamus should be targeted for the best results, and many physicians are still cautious about its use.
Houeto, J. L. et al. (2005). Tourette’s Syndrome and deep brain stimulation. J. Neurol. Neurosurg. Psychiatry. 76: 992-995.
Olson, S. (2004). Understanding Tourette’s Syndrome. Science 305: 1390-1392.