Pain has been defined by the International Association for the Study of Pain (IASP) as “an unpleasant sensory or emotional experience associated with actual or potential tissue damage.” Chronic pain is one of the most prevalent physical complaints and is loosely defined as prolonged pain of at least three months duration. Epidemiological research has estimated that 10-20% of the adult population suffers from chronic pain. The American Academy of Pain Management reported that greater than 50% of all Americans experienced recurrent or chronic pain in the past year.
Pain serves as a protective mechanism by warning us that something is not right with our bodies and prompts us to stay away from harm. Acute pain lasts for only a short duration. However, chronic pain occurs when this protective mechanism converts this normal warning sign into an unpleasant and intolerable disease.
Chronic pain can range from mild to severe, episodic or constant, merely inconvenient or completely incapacitating. Although the cause is not completely understood, in chronic pain, signals of pain remain active in the nervous system for weeks, months, or even years. This can result in physical and emotional stress on a person.
Pain treatment involves interdisciplinary care with expertise from several pain-related specialties (e.g. anaesthesiologists, palliative physicians, psychiatrists, psychologists, medical social workers, neurologists, and neurosurgeons).
Surgical Neuromodulation Pain Programme
The Surgical Neuromodulation Pain Programme at the National Neuroscience Institute (NNI) is an extension of the interdisciplinary pain service at the Singapore General Hospital (SGH) and Tan Tock Seng Hospital (TTSH).
The vast majority of chronic pain can be successfully managed with medication, physical therapy, cognitive-behavioural therapy or local nerve blocks. In selected patients who remain refractory to conventional forms of treatment, surgical neuromodulation may be considered. NNI has introduced a surgical neuromodulation programme for chronic pain patients who have exhausted all conventional approaches of treatment such as medication, nerve block injection.
Surgical neuromodulation uses advanced state-of-the-art technology. It involves the placement of an electrode on the spinal cord, on the brain or within discrete targets in the brain. A pacemaker is attached to the electrode; it generates a small amount of current to stimulate the spinal cord or brain to alleviate the pain experienced by the patient.
The types of pain syndromes treatable with surgical neuromodulation are:
Spinal Cord Stimulator
This involves placement of a stimulating electrode either percutaneously or via a small opening in the lamina of the spine (laminotomy) in the epidural space of the spinal canal. The electrode is connected to an electrical pulse generator which is implanted in the lower abdominal or gluteal region.
Motor Cortex Stimulation (MCS)
As the name suggests, a stimulating electrode is placed in the epidural space over the motor cortex at the precentral gyrus region. The electrode is connected to an electrical pulse generator which is placed over the infra-clavicular region of the chest wall.
Deep Brain Stimulation (DBS)
DBS involves highly accurate placement of a lead electrode into discrete regions of the brain. Similarly, the electrode is connected to an electrical pulse generator located over the infra-clavicular region of the chest wall.
After initial placement of the electrode, a trial period of stimulation is usually performed over 5-7 days to assess efficacy of the implant. Approximately 50% of patients will have a successful trial. Should the trial be successful, the patient will then undergo another operation to permanently implant the electrode and its pacemaker.
As with any surgery, there are risks involved. The most common complication is electrode leads migration, fracture of leads or infection. Another common complication is hardware malfunction. These problems are estimated to range from 10-15%. Other complications include an infection involving the surgical wound or nervous system, bleeding, leakage of cerebrospinal fluid, and neurological deficit. MCS and DBS involve implantation of electrodes on the surface of the brain and in the brain respectively and carries risk of seizures and brain haemorrhage. The risk of occurrence of surgical complications is about 3-5%. These complications are uncommon and can be managed successfully in most cases, although treatment may require additional surgery.
Important pointers to note in preventing leads migration: