ABSTRACT
INTRODUCTION: CHRONIC PAIN AND ITS CLASSIFICATIONPain is an innate physiologic response intended to alert the body of either imminent or ongoing tissue injury. It has both qualitative (e.g., intensity and location) and affective components (e.g., withdrawal, crying, etc.). When pain occurs spontaneously (without a physical insult) or to non-painful stimuli, or when it continues beyond the expected time course for healing of an injury, it is considered pathologic. A pathologic perception of pain that persists and interferes with daily living or causes disability can generically be termed “chronic pain.” Using this broad definition, it is estimated that 1.5 billion people worldwide and 100 million Americans suffer from chronic pain [1, 2]. Comparatively, this is nearly a fourfold increase in the number of Americans with diabetes, a fivefold increase in the number with heart disease, and ninefold increase in the number with cancer.
