There are three types of pain, based on where in the body the pain is felt: somatic, visceral, and neuropathic. Pain of all three types can be either acute or chronic. Somatic, visceral, and neuropathic pain can all be felt at the same time or singly and at different times. Most cancer patients experience both somatic and visceral pain. Only about 15–20% of all cancer patients report neuropathic pain. The different types of pain respond differently to the various pain management therapies. Somatic and visceral pain are both easier to manage than neuropathic pain.
Somatic pain is caused by the activation of pain receptors in either the cutaneous (body surface) or deep tissues (musculoskeletal tissues).
When it occurs in the musculoskeletal tissues, it is called deep somatic pain. Common causes of somatic cancer pain include metastasis in the bone (an example of deep somatic pain) and postsurgical pain from a surgical incision (an example of surface pain). Deep somatic pain is usually described as dull or aching but localized. Surface somatic pain is usually sharper and may have a burning or pricking quality.
"Viscera" refers to the internal areas of the body that are enclosed within a cavity. Visceral pain is caused by activation of pain receptors resulting from infiltration, compression, extension, or stretching of the thoracic (chest), abdominal, or pelvic viscera. Common causes of visceral pain include pancreatic cancer and metastases in the abdomen. Visceral pain is not well localized and is usually described as pressure-like, deep squeezing.
Neuropathic pain is caused by injury to the nervous system either as a result of a tumor compressing nerves or the spinal cord, or cancer actually infiltrating the nerves or spinal cord. It also results from chemical damage to the nervous system that may be caused by cancer treatment (chemotherapy, radiation, surgery). This type of pain is severe and usually described as burning or tingling. Tumors that lie close to neural structures are believed to cause the most severe pain that cancer patients feel.
Acute pain is short lasting and usually manifests in ways that can be easily described and observed. It may, for example, cause sweating or increased heart rate. It can last for several days, increasing in intensity over time (subacute pain), or it can occur intermittently (episodic or intermittent pain).
Chronic pain is defined as pain lasting for more than 3 months. It is much more subjective and not as easily described as acute pain. Effectively treating chronic pain poses a great challenge for physicians. This kind of pain usually affects a person's life in many ways. It can change someone's personality, ability to function, and quality of life.
According to the American Cancer Society, chronic cancer pain often involves persistent pain and breakthrough pain. Persistent pain is continuous and may last all day. Breakthrough pain is a brief flare-up of severe pain that occurs even while the patient is regularly taking pain medication. It usually comes on quickly and may last from a few minutes to an hour. Many patients experience a number of episodes of breakthrough pain each day.
Breakthrough cancer pain can result from the cancer or cancer treatment, or it may occur during a certain activity (e.g., walking, dressing, coughing). It also can occur unexpectedly, without a preceding incident or clear cause. Breakthrough pain usually is treated with strong, short-acting pain medications that work faster than persistent pain medications.