Some talk of two major types of pain, nociceptive and neuropathic. Distinguishing between them is important because the causes and treatments are different. Ideally, the causes of both types of pain will be identified and treated, resulting in pain relief. Unfortunately, it is often the case that cure is impossible and palliation is necessary.
Nociceptive (Tissue) Pain
Nociceptive pain results from tissue damage. Intact neurons dutifully report damage, and pain is experienced. Nociceptive pain can be subdivided into somatic and visceral (gut) pain. Nociceptive pain can be experienced as sharp, dull, or aching. There may be radiation of the pain, especially visceral pain, but it will not be in a direct nerve distribution. For example, gallbladder pain can radiate to the scapula. Nociceptive pain is generally responsive to NSAIDs (nonsteroidal anti-inflammatory drugs) and opioids. Conditions associated with inflammation, bone pain, and joint disease are particularly responsive to NSAIDs.
Neuropathic (Nerve) Pain
Neuropathic> pain may occur when there is either damage to or dysfunction of nerves in the peripheral or central nervous system. Faulty signals are sent to the brain and experienced as pain. Neuropathic pain can be either peripheral (outside the central nervous system) or central in origin. Examples of neuropathic pain include diabetic neuropathy, trigeminal neuralgia, postherpetic zoster pain (peripheral pains), and the thalamic pain syndrome (a central pain). Neuropathic pain frequently coexists with nociceptive pain. Examples include trauma that damages tissue and nerves, burns (that burn skin as well as nerve endings), and external nerve compression. Examples of the latter include tumor nerve compression and sciatica from herniated discs pressing on nerves.
Neuropathic pain is often described as having a burning or electrical quality. It may feel like a shock or lightning bolt. Sometimes stimuli that usually do not cause pain, such as light touch, may elicit a paroxysm of pain. A light stroke of the cheek that results in the sudden pain of trigeminal neuralgia is an example of this type of pain. Sometimes patients do not describe the sensation as being "painful" but rather as feeling unpleasantly strange or tingly, like an arm feels when it wakes up from "going to sleep." This is called a dysesthesia. Diabetic neuropathy commonly results in this type of sensation.
Neuropathic pain in the peripheral nervous system frequently follows a nerve distribution. This distribution may replicate a particular nerve, as in sciatic pain or trigeminal neuralgia, or may represent the distribution of terminal nerve endings, as in the stocking-glove distribution of peripheral neuropathies.
Neuropathic pain is relatively resistant to NSAIDs and opioids, although they may be helpful in certain cases. The other major classes of medications useful for neuropathic pain, tricyclic antidepressants, anticonvulsants, and sodium channel blockers, will be discussed later.
Even though the experience of pain varies from one person to the next, it is possible to categorize the different types of pain.