Thigh on Fire: Lateral Femoral Cutaneous Neuropathy
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.
(C) 2005 by Gary Cordingley