Pain is generally categorized as acute or chronic. Acute pain is associated with a medical diagnosis or condition, a medical or surgical procedure, or a disease flare of a chronic medical condition. From a perspective of the temporal course of pain, acute pain typically has a well-defined time course. Treatment is relatively straightforward, particularly for acute pain with a specific cause. Analgesic therapies, combined with treatments directed at the underlying disease, are generally effective.

Chronic pain is associated with a disease process, particularly for diseases associated with high mortality, such as cancer. Chronic pain can be associated not only with the disease process itself but with the treatment of disease. For example, various epidemiological surveys suggest that as many as 20% to 25% of patients with chronic pain related to cancer have pain related to chemotherapy, radiation therapy, and surgery

many patients still experience disabling symptoms related to the disease itself and/or to complications of chronic administration of anti-parkinsonian drugs. Hence, there is still a need to have a better understanding of the disease processes,