Dr. Ben Wedro practices emergency medicine at Gundersen Clinic, a regional trauma center in La Crosse, Wisconsin. His background includes undergraduate and medical studies at the University of Alberta, a Family Practice internship at Queen's University in Kingston, Ontario and residency training in Emergency Medicine at the University of Oklahoma Health Sciences Center.
Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.
There are numerous causes of nontraumatic leg pain, and there is no single way of classifying all of these causes. Care providers develop their own individual approach to help decide upon a diagnosis. Sometimes it can help to classify the potential causes based upon the part of the leg that hurts, whether the pain is in one leg or both, whether it is related to activity or occurs at rest, and whether underlying medical conditions exist that can precipitate leg pain.
Pain in only one leg would tend to be due to local problems and not necessarily due to a systemic (involving the entire body) illness. The presumption would be that such an illness would affect both legs. This is not necessarily always true. For example, gout (a defect in the body's ability to process uric acid) often attacks only one joint during an acute flare.
Peripheral artery disease (PAD): Pain in one leg, or both, may be due to peripheral artery disease, a decrease in arterial blood supply to the leg due to narrowing of blood vessels. Often the pain comes on with activity, since walking requires more oxygen for the muscles. If the arteries are narrow and can't supply that need, the muscles begin to ache. Blood vessels can be narrowed at any level, from the aorta (the large blood vessel that leaves the heart) to any of the branch arteries. Depending upon the level of narrowing and the particular muscles involved, the areas of perceived pain may be different.
Leg pain from peripheral artery disease that occurs with walking is called
claudication. Since peripheral artery disease usually affects many blood vessels, both legs may be affected, although the pain may be of different severity in each leg. The blood supply may decrease to the point at which pain occurs at rest, even without exercise.
Poor blood supply to the legs may also compromise the integrity of the skin and may allow infection to occur. As well, poor blood supply makes it difficult for wounds like lacerations or abrasions to heal.
Blood clot: A blood clot can completely obstruct one of the arteries to the leg and cause
the acute onset of pain because
the blood supply has been completely cut off. Aside from pain, the leg becomes
cool and pale. While there are many potential sources of a blood clot, one
common place to look is the heart. If the cardiac arrhythmia known as
fibrillation is present, there is the potential that small clots can form on the
lining of the heart and break off to travel through the arteries, obstructing
blood flow at any points distant from the heart. Aside from the leg, the obstruction
may occur in one of the blood vessels leading to the brain, causing a
stroke. A blood clot can also occur acutely in an artery that is partially narrowed. Just like arteries in the heart that can narrow over time because of cholesterol or plaque buildup, the same situation may occur in the legs. If the plaque becomes irritated or ruptures, the body can form a clot at the site, occluding the artery and stopping blood supply to the part of the leg beyond the clot.
Blood clots can also obstruct veins, causing pain. Veins return blood from the legs to the heart. There are
two systems of veins in the leg: superficial and deep. If a blood clot
occurs in a deep vein (deep venous thrombosis), it causes a
"damming" effect, and
blood is trapped behind the blockage. This causes redness, swelling, warmth, and
pain in the affected area. Calf pain and swelling are common symptoms.
Superficial veins can also clot and cause pain, but the complication of a
deep thrombosis (breaking off and embolizing to the lungs [pulmonary embolism]) does not occur with a superficial thrombosis because there are valves in the perforator veins that connect the superficial vein system to the deep system. However, if the clot develops near the groin where the two systems come together, the clot can embolize to the lungs. Superficial veins can also chronically dilate and swell and form varicose veins. Varicose veins may cause pain from this swelling and inflammation.
Low back pain: Low back pain from sciatica (inflammation of the sciatic nerve) may radiate into the buttocks and down the leg. The distribution of pain depends upon which nerve root is involved; therefore the pain may be felt in the foot, shin, or thigh. Sciatica may be caused by a variety of changes in the back from arthritis, a herniated disc, muscle spasm, or injury. The common outcome is that the space where the nerve exits the spinal canal is narrowed and there is impingement upon the nerve. Less commonly, tumors and infection can cause nerve root and spinal cord inflammation and resultant leg pain.
Neuropathy: Pain may occur from peripheral nerve inflammation not associated with the spinal cord. These conditions are known as peripheral neuropathies. This can occur from direct nerve irritation or from a medical illness. Examples of this type of isolated nerve injury include foot and toe pain from a Morton's neuroma, most frequently a thickening and inflammation of a nerve that supplies the third and fourth toes, or meralgia paresthetica that causes pain in the anterior thigh resulting from entrapment of a nerve that leaves the pelvis. Neuropathy is also seen in pregnancy when the pressure of the uterus may cause the nerve to become inflamed. These types of pain tend to involve part of one leg only. Diabetes is a common cause of peripheral neuropathy that affects both lower extremities. Alcohol abuse is another common cause of peripheral neuropathy.
Illness: Chronic illnesses like diabetes,
alcoholism, cancer, and vitamin deficiencies (for
example, B12 deficiency causing pernicious anemia)
may also result in nerve pain that often affects both legs. There are some illnesses that cause leg weakness that may be associated with complaints of leg pain, including Guillain-Barré syndrome and multiple sclerosis.
Skin: Skin inflammation may also cause significant pain, especially if there are underlying illnesses like diabetes or peripheral artery disease that prevent adequate healing. The inflammation may be due to infection often caused by
Streptococcus or Staphylococcus bacteria. Skin that is stretched due to edema or fluid accumulation in the tissues underneath the skin can cause significant pain especially when the legs are not elevated.
Shingles can cause significant pain due to inflammation of a nerve in the body. It is a reactivation of the chickenpox virus that resides in a dormant state in the body following an infection. Since it is the nerve that is inflamed, there can be significant amounts of pain. As well, a rash can occur along the course of the nerve. The rash may appear a few days after the pain begins and may resolve before the rash goes away. Sometimes the pain persists chronically.