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Meralgia Paresthetica (Outer Thigh Pain or Numbness)

Meralgia Paresthetica Definition

Meralgia paresthetica refers to unusual sensations, particularly a burning pain or numbness, in the lateral part (outer side) of the thigh due to pressure on the lateral femoral cutaneous nerve (LFCN). In some cases, trauma, stretch injury and impaired circulation to the thigh may also contribute to pain and numbness in the thigh. Also called Bernhardt-Roth syndrome, meralgia paresthetica can affect people of all races and genders. Though it can affect people of all ages, meralgia paresthetica is more commonly seen during middle age. It affects about 4 to 5 out of every 10,000 people annually. Around 250 per 100,000 diabetic patients develop meralgia paresthetica.

Meralgia Paresthetica Pathophysiology

TheĀ  lateral femoral cutaneous nerve carries sensation to the skin of the thigh. This nerve goes through inguinal ligament – s a fibrous tissue that supports the groin region between the abdomen and the thigh. If the lateral femoral cutaneous nerve is compressed or injured near the inguinal ligament for long periods, it can result in pain and other sensations.

The LFCN starts from a nerve network called lumbar plexus and runs through the pelvis lateral to the psoas muscle. This muscle is like a rope running obliquely from spine to the thigh bone or femur. The lateral femoral cutaneous nerve passes to the thigh through a tunnel, which is formed by the side of the inguinal ligament and the front part of a spine bone called ilium. At this point of crossover, LFCN sometimes gets trapped. This compression results in meralgia paresthetica.

Picture from Wikimedia Commons

Meralgia Paresthetica Symptoms

Compression of the lateral femoral cutaneous nerve may cause the following symptoms :

  • Numbness, pricking, or tingling in the outer part of the thigh
  • Burning pain in the outer part of the thigh
  • Pain spreading across the buttocks
  • Dull pain in groin area
  • Pain only on one side of the body (in majority of the cases)
  • Increase in pain upon walking or standing
  • Relief from pain felt upon sitting
  • Hypersensitivity to heat or light touch (less common)

Meralgia Paresthetica Causes

The lateral femoral cutaneous nerve solely carries signals of sensations, meaning that it is a sensory nerve. If it is pinched or compressed, it can result in pain, tingling, pinching, numbness and other sensations specific to meralgia paresthetica.

Such compression on LFCN may result from following causes:

  • Tight pants and related lower body garments
  • Pregnancy
  • Obesity
  • Injury or past surgery resulting into scar tissue near the inguinal ligament
  • Walking, standing or cycling for too long
  • Nerve injury due to diseases that affect the nerves like diabetes mellitus)
  • Automobile accidents causing thigh and nerve injury
  • Tight belts (waist)
  • Lying in the fetal position for long periods of time
  • Tumors near the lateral femoral cutaneous nerve (in rare cases)
  • Leg exercises, which increases tension on the inguinal ligament

Meralgia Paresthetica Risk Factors

The following conditions increase the risk of developing meralgia paresthetica:

  • Obesity: Excess body weight puts more pressure on lateral femoral cutaneous nerve.
  • Pregnancy: Increasing body weight and changed posture during pregnancy puts extra pressure on the groin and LFCN.
  • Diabetes: Diabetes increases the risks of all kind of nerve injuries. A LFCN injury can result in meralgia paresthetica.
  • Age: People aged 40 to 60 years are at a higher risk of developing meralgia paresthetica.

Meralgia Paresthetica Diagnosis

A physical examination and a thorough assessment of the medical history helps in diagnosing meralgia paresthetica. In 80% of patients, only one leg is affected and the other leg does not show any symptom. In such cases, the sensory differences between the affected leg and the other leg are checked.

Following tests may be conducted to exclude other conditions that may result in similar pain:

  • X-rays can detect bone abnormalities in pelvic area and hip, which might put pressure on the nerve.
  • Electromyography (EMG) test determines the electrical discharges generated in muscles. In this test, a needle-like electrode is inserted through the skin into the muscle tissue. The electrical activity of the muscles is then studied when the muscle is working and when it is at rest. This test gives normal results in patients of meralgia paresthetica. In meralgia paresthetica only LFCN is compressed and no muscles are affected. It can thus distinguish between meralgia paresthetica and other muscle disorders.
  • Nerve conduction velocity (NCV) test studies the speed of signal transmitted through a nerve. Nerve conduction test can detect meralgia paresthetica by giving small electrical shocks to the patients. In case of a damaged or injured lateral femoral cutaneous nerve, the speed of signals will be different.
  • Imaging studies like computed tomography (CT) scan or magnetic resonance imaging (MRI) can detect the presence of tumors, which might put pressure on the lateral femoral cutaneous nerve.

Meralgia Paresthetica Treatment

Treatment aims to ease and pressure from on the lateral femoral cutaneous nerve. Medical treatment is the main approach in combination with other measures, which aims to relieve inflammation and pain. However, the underlying cause needs to be identified and attended to for long term management of meralgia paresthetica

Lifestyle measures

Wearing loose clothing, avoiding tight belts, and reducing body weight helps in relieving pressure from the LFCN. In some weeks or moths, the pain may go away. However, depending on the extent of pain, less physical activity to absolute bed rest may be recommended to the patient till the medical treatment can achieve its goals.

Medications

Some over-the-counter pain relievers (like acetaminophen, ibruprofen, or aspirin) may help give relief from the pain.

  • Corticosteroid injections decrease inflammation and relieve pain. They may have side effects like nerve damage, joint infection, pain, and discoloration of skin at the injection site.
  • Application of lidocaine at the inguinal ligament temporarily relieves the symptoms. Both corticosteroids injections and lidocaine provide relief lasting for several weeks.
  • Tricyclic anti-depressants are sometime given to relieve the pain. They may have side effects like constipation, dry mouth, drowsiness, and weakened sexual functioning.
  • Anti-seizure drugs like pregabalin may be beneficial in rare patients.
  • Neurogenic pain medications (carbamazepine, gabapentin) are prescribed to some patients to lessen the pain. Side effects of these medications include constipation, dizziness, nausea, lightheadedness, and drowsiness.

Surgery

Surgical decompression of the nerve is considered in rare cases. Surgery is recommended to patients with severe, long-lasting, and treatment-resistant symptoms. Surgery might result in side effects like permanent numbness in the thigh region. Recovery of meralgia paresthetica patients may take several weeks to months, depending on the severity of nerve damage.

References :

http://www.mayoclinic.com/health/meralgia-paresthetica/DS00914/DSECTION=causes

http://emedicine.medscape.com/article/1141848-overview

http://www.patient.co.uk/doctor/Meralgia-Paraesthetica.htm