Types of Pain

Pain may be classified according to location (somatic, visceral or nerve pain) or the length of time it has been present (acute or chronic). Most people will experience three or four different types of pain every year.

Somatic Pain (musculoskeletal pain) - refers to pain involving the skin, muscles, joints, bones and ligaments. It does not include the organs or nervous system. Pain receptors located in the musculoskeletal system respond to touch, heat, cold, vibration, stretch (muscles), inflammation (e.g. cuts and sprains) and oxygen starvation (ischemic muscle cramps). Somatic pain is often sharp and well localized. It can often be reproduced by touching or moving the area or tissue involved. Somatic pain responds well to acetaminophen or NSAIDS (non-steroidal anti-inflammatories-aspirin, ibuprofen, naproxen etc) or opioids (narcotics like morphine).

Visceral Pain refers to pain in the internal organs. The body is frequently divided into three categories when considering the internal organs. They include:

• The thorax (heart and lungs)
• The abdomen (liver, kidneys, spleen and bowels) and
• The pelvis (bladder, womb, and ovaries).

Pain receptors in the internal organs respond to stretch, inflammation and oxygen starvation (ischemia). Organ pain can be difficult to pinpoint since it is often felt in an area other than the one being stimulated. This is called 'referred pain.' For instance pelvic pain is sometimes felt in the lower back; abdominal pain is sometimes be felt in the mid-back and thoracic pain may be felt in the upper back, shoulders or arms. Organ pain may be experienced as a vague deep ache or it may be cramping or colicky in nature. Weak or strong opioids (narcotics like morphine) are generally effective for organ pain.

Nerve Pain (neuropathy, neuralgia, neuritis) - Nerves can be more than messengers of pain; they can become the source of pain. Nerves do not have nociceptors that respond to pain like those found in the skin, muscles, bones, ligaments and organs. However damaged nerves may become unstable and start sending signals to the brain that are interpreted as pain. Nerve pain is often described as tingling, numbness, burning, shooting, sharp-cutting, darting and hypersensitive.

Nerves are divided into two systems:

• The peripheral nervous system - nerves that go from the outer areas of the body (skin, bone, muscle, organs etc) to the spinal cord
• The central nervous system - nerves that go from the spinal cord to the brain

Causes of nerve pain include:

• Damage to nerves (i.e. cut, burn)
• Nerve pressure (trapped nerve)
• Nerve inflammation (injury, disease)
• Nerve infection (viral illness i.e. shingles)

Acetaminophen, NSAIDs (ibuprofen, naproxen, aspirin etc) and opioids (narcotics-morphine) often provide only partial relief of nerve pain. However, antidepressants, anticonvulsants, antiarrhythmics, NMDA antagonists and topical capsaicin may provide additional relief.

When physicians recommend antidepressants for pain, patients often mistakenly think their health care provider believes 'it is all in their head'. This is not the case. Antidepressants can relieve nerve pain whether or not depression is present.

Sympathetic Pain is nerve pain that involves the nerves of the sympathetic nervous system (SNS). The sympathetic nervous system is made up of nerves that control the blood supply to the muscles and skin, controls sweating and prepares the body for the 'flight or fight' response. Sometimes fractures or soft tissue injuries (stab wounds) damage the sympathetic nerves, resulting in hypersensitivity at the site of the injury and the area nearby. Sweating and body temperature control are affected and pain is often severe. Sympathetic pain responds to the same types of medications used to treat other types of nerve pain.

Vascular pain - Vascular pain develops when the communication between blood vessels and nerves is interrupted or damaged by disease or injury. Examples of vascular pain include pain caused by coronary artery disease (angina), vasculitis (inflammation of the blood vessels), injuries (cuts, stab wounds, surgery) and circulatory problems (arteriosclerosis). Vascular pain is often ischemic in nature, since poor circulation starves the area of needed oxygen. Nerve pain is commonly associated with vascular pain.