Referred pain is a symptom where a patient perceives pain in a location other than where the painful stimulus is. One well known example of this phenomena is phantom pain in a limb that has been amputated. Another is the way that a heart attack can cause pain in the neck, shoulders, and back. However, it occurs in other circumstances as well. One routine and well known example is how a blow to the testicles is felt in the abdomen.
Medicine has known about the phenomena of referred pain since the 1880s. However, despite 120 years of research on the subject, its mechanism remains a mystery. However, it rarely occurs in a healthy individual, and is common in patients who suffer from chronic diseases of the muscles.
Some other examples are:
- "Brain freeze", where rapid cooling and reheating of the sinuses and trachea typical of eating ice cream is perceived as pain in the brain.
- Diseases of the gallbladder or liver often cause pain in the right scapula (shoulder blade).
- Injuries to the lungs or diaphragm are often perceived as pain in the left shoulder.
- An injury to the testicles is perceived in the abdomen as the nerves in the former run through the latter.
Other conditions that cause referred pain are nerve damage, damage to the esophagus, prostate disease, and fibromyalgia.