Definition
Idiopathic Parkinson’s disease (PD) is a diffuse neurodegenerative brain disease affecting olfactory, autonomic, limbic, and somato-motor components of the central nervous system.
Deep Brain Stimulation (DBS) is a neurosurgical procedure involving the implantation of electrodes within the brain. Through electrical stimulation of specific deep-located targets (brain nuclei) DBS attempts to restore and modulate pathological electrical brain networks in many movement and neuropsychiatric disorders.
Epidemiology
PD affects 6 million people globally. Age-standardised prevalence rate for subjects 65 years or older is 1-2%. Male are more often affected than female (ratio 3:2). PD must be differentiated from other similar conditions, the so-called secondary Parkinsonisms.
Etiology
PD primary symptoms result from the loss of dopamine secreting cells in the SNpc (pars compacta of the substantia nigra) due to the abnormal accumulation of alpha-synuclein protein. SNpc is one of the main modulator of the basal ganglia network and its pathological activity leads to an imbalance between excitatory/inhibitory signals within basal ganglia and between basal ganglia and cortical structures.
Diagnosis and pharmacological treatment
Diagnosis is mainly based on clinical information and neurological examination (tremor, bradykinesia, rigidity and postural instability). Other common symptoms may be hyposmia, constipation, depression and REM sleep behaviour disorders. Once the diagnosis is established, pharmacological therapies include dopamine agonists, monoamine oxidase B (MAO-B) inhibitors, and the mainstay of treatment, carbidopa/levodopa
Surgical Treatment (DBS/Ablation)
Surgical treatment is reserved for those patients whose symptoms cannot be adequately controlled with medications, or whose medications have severe side effects. Surgery for PD can be divided in two main groups: ablative and Deep Brain Stimulation. Nowadays the latter is preferred due to its reversibility and low risk of complications.
DBS surgical technique
Procedure: Stereotactic positioning of stimulating microelectrodes
Rationale: Modulation of neuronal activity obtained by modifying the release of neuromediators
Features: High Frequency (130Hz) and Low Voltage (DC) Voltage (1-3.5V).
The patient must be awake and all dopaminergic medications must be withheld at least 12 hours before the procedure. Surgery may be performed in two different modalities: frame-based (application of a stereotactic head frame such as Leksell or CRW frame) or frameless (application of cranial fiducials and use of image-guided neuronavigation systems). Frame-based technique is still considered the gold standard due to its superior accuracy. The stereotactic frame is applied under local anestetic.
Description of the Surgical Procedure
A stereotactical CT scan is performed and then fused with the volumetric MRI (T2, T1 with gadolinium and IR sequences) obtained the day before surgery. Targeting of the nucleus may be performed both in a indirect (stereotactic atlas) and direct way (direct visualisation of the nucleus on radiological images). Electrophysiological and stimulation test will confirm the correct placement of the electrode during surgery. The main nuclei in DBS surgery for PD are the subthalamic nucleus and the internal globus pallidus.
Results
After DBS for PD motor scores show on average an improvement up to 69%, a dyskinesia reduction of 20-90%, and levodopa equivalent reduction up to 71%.
Authors
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Vincenzo Levi, MDNeurosurgeon Resident |
