The full potential of intraoperative neurophysiology is realized during the performance of so-called functional neurosurgical procedures. During these interventions therapeutic lesions or stimulating electrodes are stereotactically placed within deep brain structures to treat movement disorders such as Parkinson’s disease (PD), essential tremor (ET), dystonia, affective disorders, and chronic neuropathic pain.
The deep location of these structures precludes direct surgical approaches. Instead, surgeons rely on a combination of image-guided stereotactic techniques and intraoperative neurophysiology to place the therapeutic lesions or stimulating electrodes with acceptable accuracy and safety. Unlike tumors, which are relatively large and easily identified on CT or MRI, functional neurosurgical targets typically are small and poorly visualized with current imaging modalities. Moreover, because these are physiologic as much as anatomic targets, image-based targeting may incompletely identify the desired location. Consequently, intraoperative recording and stimulation techniques have been developed to aid target localization. These techniques complement anatomical targeting by providing real-time electrophysiological data concerning probe position and the surgical target. The surgeon and physiologist use these data to “fine-tune” their anatomic targeting before completing the therapeutic intervention. Thus employed, intraoperative neurophysiology does not simply monitor surgical activity; it guides it.

Pain is a major public health problem. It is the most common symptom for which patients seek medical care and the primary complaint of approximately half of all patients who visit a doctor. Several surveys conducted in European countries have found that nearly 50% of adults suffer from one or more types of pain or discomfort at any given point in time.
Chronic pain is defined as pain that lasts for more than six months and does not respond to medical therapy. It may result from either a previous injury long since healed or it may have an on-going cause, such as nerve damage, cancer, chronic infection or failed back surgery syndrome (FBSS).
Chronic pain can have a drastic effect on a patient’s quality of life. Severe chronic pain may weaken a patient’s physical and psychological health far beyond that which might be expected for the patient’s underlying disease.

Physical problems
Patients who suffer from chronic pain are more likely to be in poor general health. This is the result of negative health consequences associated with
unrelieved pain, including:
● Increased stress, metabolic rate, blood clotting and water retention
● Delayed healing
● Hormonal imbalances
● Impaired immune system and gastrointestinal functioning
● Increased heart rate and blood pressure
● Increased blood sugar
● Decreased digestive activity
● Reduced blood flow
● Loss of function and atrophy

Psychological problems
Chronic pain is often associated with a long history of psychological and social problems. Patients with chronic pain may lose their jobs and income. In addition, pain can lead to emotional distress and a deterioration in family and social life, while preoccupation with pain can lead to a downward
spiral of irritability and depression.

For patients with chronic pain, pain management typically involves a combination of physical therapy, oral medication and other conservative therapies. Some patients will need surgical intervention to address the mechanical condition causing the pain, whereas others may require advanced interventions. Neurostimulation and intrathecal drug delivery (IDD) often offer alternatives to destructive procedures or sometimes more costly spinal surgeries in appropriately selected patients. Although pharmacotherapy pain treatment may reduce pain, it may also be associated with adverse effects that will impact on a patient’s quality of life. Common adverse effects of pain management strategies include reduced alertness or mobility, dizziness or mental confusion, nausea, vomiting, constipation or urinary retention, and motor and sensory loss or weakness.

Treatment of chronic pain typically involves a multidisciplinary approach. Management of chronic pain patients with neuromodulation or IDD requires the interaction of many specialists on a multidisciplinary team. The team draws on the expertise of these specialists with the goal of achieving an effective level of pain relief for the patient. The key members of the team are referring physicians, who typically are involved in all aspects of chronic pain treatment; implanting physicians (normally anesthesiologists, neurosurgeons, spine surgeons and general surgeons) and nurses with skills and training to implant products for neurostimulation and intrathecal drug delivery; and other personnel who work closely with patients, in particular, the patient management co-ordinator.