Referred pain is pain felt at a site other than where it originates. Referred pain can be:
Visceral pain originates in internal organs but may be felt on the surface or appear to come form another structure such as a muscle or joint. Examples in include angina or heart attack pain which can be felt not only over the front of the chest but in the jaw, teeth, upper back, down the arm or in the throat. Another example is earache which may arise from the tongue, throat, neck or jaw joint (TMJ). Gallbladder pain may be felt in the shoulder blade. Gynecological pain can be felt in the lower back or thighs as well as the lower abdomen. Shoulder pain can be referred from the neck, chest, heart or diaphragm, including infections or bleeding in the abdomen which irritate the diaphragm. This is why when you see a doctor for apparent musculoskeletal pain he or she will likely ask questions intended to rule out some of these conditions. Occasionally, the skin over an affected organ will be affected (the viscero-cutaneous reflex).
Dermatomal pain arises from an injury or irritation/inflammation of a nerve in the spinal cord (or face) and is felt along the area of the skin which corresponds to the nerve. Shingles is one such example; a disc herniation also produces similar pain which will be felt in the arm (in the case of neck spinal roots) or down the the leg, as in the case of lower back nerves (lumbar and first sacral nerve roots). If the nerve is compressed sufficiently then numbness may occur instead of pain.
Joint pains can be referred from one joint to a neighbouring one and present a confusing picture. One common example is hip arthritis which is felt in the knee (or vice versa) or lower back degenerative arthritis which can refer to the hip or thigh. A normal joint (e.g. the knee) is painful and the abnormal one (e.g. the hip) is stiff but not painful and in this case the knee pain resolves when the hip is treated. Don't be surprised if your MD wishes to examine the joint above and the joint below the one you are complaining about. Teasing out where the pain is coming from can be difficult when both joints are involved.
Muscular or myofascial ('myo'=muscles; 'fascial' refers to the thick white connective tissue which envelopes all our muscles, nerves, organs etc) trigger points, when active, can refer pain in particular predictable patterns which can mimic dermatomal patterns or other conditions. For example, trigger points in the scalene muscles and pectorals major can refer down the arm; some neck muscles can give rise to pain in the upper jaw (resembling toothache) or forehead. Pain patterns arising from specific ligaments have also been mapped out.
Sclerotomal referred pain arises from specific spinal segments and tends to be dull, poorly localized and overlaps with other levels.
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