At the age of 32 Sigmund Freud developed a new problem. Pricking and other unpleasant sensations had overtaken the skin on the outer side of his right thigh. Walking made his symptoms worse. The affected skin was exquisitely sensitive to touch and even the usual rubbing of his underclothes irritated the area.

Seven years later in 1895, when Freud wrote up his self-observations for a German medical journal, the abnormal sensations were still present, but had migrated.

At first, the area of disturbance had been more noticeable near the top of the thigh, but gradually the abnormal sensations moved downward to a palm-sized area a hand’s breadth above the side of his knee.

When Freud squeezed a fold of skin in this area, it hurt more than it did in his left thigh. Although he could feel a pinprick as such, it also burned. Even so, individual spots within the zone of abnormal skin were insensitive to ordinarily painful maneuvers. He also noticed that temperature sense was impaired. Warm objects placed against the affected skin felt cooler than in unaffected areas. And although the original pricking sensations improved over time, his outer thigh had become generally less sensitive to usual stimulations.

Freud’s physician, Josef Breuer, found that the affected skin was in the territory of the lateral femoral cutaneous nerve, a nerve that concerns itself with sensation only and has no muscular connections.

Dr. Breuer concluded that Freud’s symptoms were caused by damage to this nerve. Dr. Breuer also suspected that the nerve might be particularly vulnerable to injury in the groin near the front of the hip where it passes between strands of a ligament. As a result, he thought that wearing tight clothing might aggravate the condition.

Our understanding of this disorder has changed little in the 110 years since Freud wrote his report for Berlin’s “Neurologisches Centralblatt,” or in the 20 years since Francis Schiller, M.D., translated it into English for the American journal “Neurology.”

To set the record straight, Freud and Breuer were not the first to recognize this condition.

Max Bernhardt of Germany first wrote about it in 1878 and in 1895 Vladimir Roth of Moscow named the condition “meralgia paresthetica,” a term still in use. This name is the sum of its three parts. “Meros” is Greek for thigh, “algos” is Greek for pain and “paresthetica” means unprovoked sensations. This entrapment neuropathy (pinched nerve condition) was one of the first to be recognized as such.

The lateral femoral cutaneous nerve is formed in the lower back from branches of the second and third lumbar spinal nerves which combine to form a single nerve (on each side) soon after emerging from the spinal column. The nerve passes through the interior of the pelvis and exits the pelvis near the outer border of the inguinal (groin) ligament before making a downward turn to run beneath the skin of the outer thigh.

The course of the nerve can vary from person to person and even from side to side in the same person. In about 25% of people the nerve splits into branches before reaching the inguinal ligament, and there can be up to 5 branches. This variability might make some people more vulnerable to nerve-injury than others.

Pressure within the pelvis, as from pregnancy, obesity and (rarely) tumors, can injure the portion of the nerve within the pelvis. And as Freud’s physician surmised, the nerve is particularly vulnerable to injury from external pressure at the inguinal ligament, as from corsets, wide belts and tight pants. However, a cause for meralgia paresthetica is not always found, as was apparently the case when Freud had it.

The nerve can also be injured during a wide variety of surgical procedures, including orthopedic, vascular, gynecological, abdominal, hernia and even stomach-stapling operations.

In a recent series of spinal surgery cases in Taiwan, 60 out of 252 patients experienced meralgia paresthetica as a complication of the surgery. Fortunately, in all cases it resolved within two months.

Diagnosis of this condition is usually made from the history and the physical examination, with the key features being numbness and unpleasant sensations on the side of the thigh. Other conditions can mimic meralgia paresthetica, for example, a pinched spinal nerve in the lower back, or impairment in the nearby femoral nerve that also emerges from the pelvis at the inguinal ligament. Tests of muscle and nerve electricity–electromyography and nerve conduction studies–can help resolve ambiguous cases.

Treatment of meralgia paresthetica has not been studied by the gold-standard method of randomized, controlled trials involving a comparison group of untreated patients. So in choosing appropriate treatment all we have to go on are collections of cases published in medical journals. Because many cases turn out well without drastic treatments, conservative approaches are tried first. Weight loss, removal of tight garments, completion of pregnancy and simple watchful waiting can all be effective.

While awaiting a favorable outcome, symptoms can be managed with skin-patches containing a local anesthetic drug, anti-inflammatory medications, certain epilepsy and antidepressant drugs known to relieve nerve-pain, and local injections with steroids. Surgery to relieve the pinch is usually reserved as a last resort.