Motor Cortex Stimulation (MCS)

Motor cortex stimulation is a relatively new treatment for a number of therapy resistant pain syndromes. It involves an electrode placed under the skull on the meninges located above primary motor cortex. To this end a small window is made in the skull. The motor cortex lies in the frontal lobe on the precentral gyrus. The electrodes conduct currents, which cannot be perceived by the patient. The pain reduction is not instantaneous, but occurs after several minutes.

The mechanism behind motor cortex stimulation

The effects MCS has on pain has been described in a number of studies. The precise mechanism through which this happens remains to be unveiled. However, there are several hypotheses:

• suppression of neuronal activity in the thalamus (central brain area involved in pain perception),
• recovery of inhibiting (painsignal-suppressing) pathways,
• increased blood flow in thalamus, gyrus cinguli, frontal cortex and brain stem (areas involved in the central processing of incoming stimuli (including pain),
• change in pain perception at cognitive and affective level.

Who is motor cortex stimulation for?

Based on clinical studies to date, two important indications exist for MCS:

• therapy resistant pain especially in the upper body on one side, after a brain hemorhage or infarct,
• therapy resistant facial pain (atypical trigeminal neuralgia).

There are several conditions that can be a reason to not treat patients with MCS:

• the use of therapeutic anticoagulants
• severe cognitive dysfunction and/or psychiatric problems making evaluation difficult,
• paralysis of the painful region,
• pain as a result of tissue damage,
• epilepsy (uncontrolled)
• life expectancy less than 3 years,
• presence of a pacemaker or other neuromodulation system,
• severe cardio-pulmonary comorbidity/contra-indication anesthesia,
• presence of previous cerebral implants, which hinder adequate neuro-imaging,
• severe cerebral atrophy,
• alcohol abuse,

The procedure

The patient will be referred to the pain clinic for examination and information. Subsequently, an extensive consult will take place at the neurology outpatient clinic. Hereafter, a decision will be made about further examination and treatment in consultation with the anesthesiologist, neurologist, neurosurgeon and a psychologist. The preparatory examination consists of two parts. An outpatient part, where, besides informing the patient, the initial screening for suitability of the patient will take place, as well as a neurological and psychological examination. In a clinical part additional diagnostics will be performed and the actual operation will take place.

Before the operation

In order to find the right location for the placement of the MCS electrode, the functional/anatomical features of the brain will be determined using different techniques. With MRI, both anatomical as well as motor functions  (fMRI) of the cortex will be mapped. Using SSEP (somatosensory evoked potential) a reaction in the cortex can be detected following the stimulation of a nerve in the arm region. Finally, with the use of transcranial magnetic stimulation the motor cortex can be stimulated electrically through the skull and the skin. Through a reaction of a muscle it will be visible which part of the cortex corresponds with the painful area. 

During the operation

The placement of the MCS system takes place under general anesthesia. The neurosurgeon opens the skull and locates the motor cortex. After the correct location has been found, the electrode is attached to the meninges. A pulse generator is then placed under the collar bone. This pulse generator consists of a battery, an antenna and a microprocessor which controls the electrical stimulation program. The pulse generator is then connected to the electrode subcutaneously. 

Results of motor cortex stimulation

Due to the fact that MCS is a relatively new technique, there are no results from large groups of patients. However, there is a tendency that 50 to 60% of the people with intractable neuropathic pain do report a significant reduction of the pain with MCS. Patients are not pain free, but more than half the MCS users require less medication than before.
To the question whether the patients would go through the whole procedure, knowing their results beforehand, an even greater percentage answers 'yes'. 

Side effects

The most common side effects are short generalized epileptic seizures and infections. Both can be occur during the first period after implantation. The patient does not feel the stimulation of the cortex itself.

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