Chronic pain falls into a couple of broad categories. These categories help doctors treat the pain because every type must be approached and treated differently. The generally accepted forms of chronic pain are:

• neuropathic pain: Pain caused by damage to or malfunction of the nerves themselves. The peripheral nerve system includes all the nerves that lead to and from the spinal cord. These nerves transmit pain signals to the brain. If they're injured, neuropathic pain may develop—pain caused by injury to the nerves themselves. You may also hear the term peripheral neuropathy, which is another way to say neuropathic pain, since it is damage to the peripheral nervous system. Damage to the central nervous system can also trigger neuropathic pain. Chronic neuropathic pain can be especially challenging to treat because it can be difficult to pinpoint where and how the nerves are damaged.

• nociceptive pain: Nociceptors are the receptors in the nervous system that get activated when there's an injury. If there is no injury from outside the nervous system, the nociceptors aren't active. Nociceptive pain, then, is pain caused by an injury to something other than the nerves. In chronic pain, though, the nociceptors may still be sending pain messages long after the original injury has healed.

• somatic pain: "Soma" means "body," so somatic pain comes from injuries to the outer body—skin, muscles, ligaments, tendons, joints, bones, etc. It's generally easy to identify where somatic pain comes from, and the pain can be sharp or throbbing (depending on what part of the body is injured).

Bone pain is a somatic pain. Bones can ache. If the bones have been If the bones were weakened by another condition, such as cancer or osteoporosis, then you can have a very achy and very intense dull pain. Bone pain can also be acute: if you break a bone, for example, that is acute pain. If the bone heals, but you still have a throbbing pain (it may be constant, or it may come and go), that can be considered chronic bone pain.

Muscle pain is somatic pain. Chronic muscle pain is more than a strained muscle. Your muscles may have a chronic muscle spasm that causes them to be tense. This form of muscle overload can cause long-lasting pain, especially in the back. Muscle pain can also develop as part of certain chronic conditions, such as fibromyalgia.

• visceral pain: Your viscera are your internal organs—specifically those contained in your abdomen and chest cavity. The stomach is an example of a visceral organ. Not every organ has nociceptors, so not every internal organ can send pain messages if it's been injured (the lungs, for example, don't have nociceptors).

However, if you injure an organ that has nociceptors, you will probably feel deep, achy pain, and it will be hard to pinpoint where the pain is coming from. Visceral pain can also have referred pain. That means that the brain can't distinguish the pain from the organ from pain from another part of your body. For example, if you have a kidney problem, your low back may be painful.

Figuring out what type of chronic pain you have can be a difficult process, especially since many types of chronic pain may not come from any noticeable injury or disease. Also, since pain is such a subjective experience, you must be thorough in describing your pain to the doctor. Working together, you and the doctor can figure out the best way to deal with your chronic pain.