Pain is an unpleasant sensation that can negatively affect all areas of a person's life, including comfort, thought, sleep, emotion, and normal daily activity.1 Pain, as defined by the International Association for the Study of Pain, is, "An unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage. Pain is always subjective." Because pain is a variable and personal experience, it is difficult to completely describe and measure objectively. The clinician must therefore guard against personal biases, which can interfere with treatment. One must also rely on tools such as pain scales to communicate with patients and understand the extent of their pain.
Pain is categorized according to its cause, location, duration, and clinical features. The most simplistic categorization involves differentiating brief-duration (acute) pain from long-lasting (chronic) pain.1-2 Other types of pain include visceral, somatic, and neuropathic.
Acute pain results from injury or surgery. Acute pain is limited in duration and associated with objective features, such as increased heart rate, pulse pressure, anxiety, and/or sweating. Acute pain is intense at the beginning and will decrease in intensity over time or become intermittent depending on the individual's activities.
Chronic pain is a long-term experience, and sometimes subjective. A chronic disease that is characteristically painful for which there is no cure may lead to chronic pain, examples include: arthritis, cancer, migraine headaches, fibromyalgia, and diabetic neuropathy. Psychological conditions such as depression may exacerbate or cause chronic pain.
Visceral pain results from stimulation of internal organ pain receptors. Examples are pancreatic cancer pain or cancer metastases. The painful stimuli from the internal organ receptors enter the spinal cord at multiple levels along with somatic fibers, and therefore patients may describe the sensation as pressure-like, deep squeezing, and usually not very well localized or defined. In general, the patients often cannot pinpoint the source of the pain.
Somatic pain originates from irritation of pain fibers in the body surface or deep tissues. Examples are surgical incisional pain or surgical bone pain. Painful stimuli enter spinal cord at a single level, and the painful stimuli can be mapped on parietal cortex. The patient may describe the pain as sharp, piercing from body surface or dull aching from deep tissues, and the individual can usually pinpoint the precise location of the painful origin.
Neuropathic pain can be initiated or caused by a primary lesion, dysfunction, or transitory alteration in the peripheral or central nervous system resulting in sensations of burning, tingling, or electric shock-like quality. These sensations can be triggered by very slightest touches that are normally tolerated, and result in an exaggerated painful sensation.