Movement disorders are neurological conditions that affect the speed, fluency, quality, and ease of movement.
see also Pediatric movement disorders
Movement disorders include the following conditions:
Ataxia (lack of coordination, often producing jerky movements)
Dystonia (causes involuntary movement and prolonged muscle contraction)
Huntington's disease (also called chronic progressive chorea)
Multiple system atrophies (e.g., Shy-Drager syndrome)
Myoclonus (rapid, brief, irregular movement)
Progressive supranuclear palsy (rare disorder that affects purposeful movement)
Restless legs syndrome (RLS) and reflex sympathetic dystrophy/periodic limb movement disorder (RSD/PLMD)
Tics (involuntary muscle contractions)
Tremor (e.g., essential tremor, resting tremor)
Wilson disease (inherited disorder that causes neurological and psychiatric symptoms and liver disease)
Common dystonias include spasmodic torticollis, which affects muscles of the head, face, and neck, and blepharospasm, which causes involuntary closing of the eyelids.
Tourette's syndrome is an inherited disorder characterized by multiple motor and vocal tics (repeated muscle contractions).
Symptoms of Tourette's usually develop during childhood or early adolescence. Patients with the disorder often develop behavioral problems such as hyperactivity, inattention, impulsivity, obsessions, and compulsions. In most cases, symptoms vary in frequency and in severity.
Tics are involuntary muscle contractions that interrupt normal activities. They often are preceded by a strong sensation or urge that is temporarily relieved following the muscle contraction. Examples of common tics include the following:
Clearing the throat
Shrugging the shoulders
Over the past years, research into the neurophysiology of the basal ganglia has provided new insights into the pathophysiology of movement disorders. The presence of pathological oscillations at specific frequencies has been linked to different signs and symptoms in PD and dystonia, suggesting a new model to explain basal ganglia dysfunction. These advances occurred in parallel with improvements in imaging and neurosurgical techniques, both of which having facilitated the more widespread use of DBS to modulate dysfunctional circuits. High-frequency stimulation is thought to disrupt pathological activity in the motor cortex/basal ganglia network; however, it is not easy to explain all of its effects based only on changes in network oscillations 1).
Deep brain stimulation (DBS) is now well established in the treatment of intractable movement disorders.
The first surgical procedures for abnormal movement disorders began in the 1930s, when surgeons first proposed ablative techniques of the caudate nucleus or transection of motor (pyramidal) pathways to reduce involuntary movements in patients with Parkinson's related tremor. During the 50-year interval between 1945 and 1995, the development of precise intracranial guiding devices, brain maps, and advanced imaging led to the refinement of appropriate deep brain targets affecting extrapyramidal pathways. Lesional surgery and subsequent neuroaugmentation using deep brain stimulation extended the role of deep brain surgery for a wider group of patients with tremor, rigidity, dyskinesia, and other involuntary movement disorders. Stereotactic radiosurgery has had wide application for tremor. The history of movement disorder surgery reads like a who's who of brilliant and resourceful surgeons who pushed the frontiers of neurosurgery. Even today, practitioners of functional brain surgery are among the most innovative practicing neurosurgeons 2).
Walker et al., reviewed 384 electrode implants for movement disorders, characterized the presence or absence of stimulus amplitude thresholds for dose-limiting DBS side effects during surgery, and measured their predictive value for side effects during device activation in clinic with odds ratios ±95% confidence intervals. They also estimated associations between voltage thresholds for side effects within participants. Intraoperative clinical response to macrostimulation led to adjustments in DBS electrode position during surgery in 37.5% of cases (31.0% adjustment of lead depth, 18.2% new trajectory, or 11.7% both). Within and across targets and disease states, dose-limiting stimulation side effects from the final electrode position in surgery predict postoperative side effects, and side effect thresholds in clinic occur at lower stimulus amplitudes versus those encountered in surgery. In conclusion, awake clinical testing during DBS targeting impacts surgical decision-making and predicts dose-limiting side effects during subsequent device activation 3).