What is meralgia paraesthetica?

Meralgia paraesthetica is a neurological (nerve) condition that causes an area of skin over the upper outer thigh to become painful, numb or tingly.

Meralgia paraesthetica is known as a nerve entrapment syndrome. This means it is a collection of symptoms caused by a trapped (or compressed) nerve. The trapped nerve in question is called the lateral cutaneous nerve of the thigh (also known as the lateral femoral nerve).

What is the lateral cutaneous nerve of the thigh?

The lateral cutaneous nerve of the thigh is found in the upper leg. It provides sensation to an area of skin on the upper outer thigh. If this nerve is trapped or compressed, burning pain, numbness or tingling might be felt in the area of skin supplied by the nerve. These symptoms constitute meralgia paraesthetica.

The lateral cutaneous nerve of the thigh is a sensory nerve that supplies the skin. It starts off in the lower part of the spinal cord, in the lumbar region. It has to pass over the front of the hip bones, and under the inguinal ligament before reaching the thigh. The inguinal ligament is a tough fibrous band in the groin. This is the site at which the nerve is most commonly compressed or trapped.

What causes meralgia paraesthetica?

Most cases have no identifiable cause.

Meralgia paraesthetica can, however, be caused by direct injury to the lateral cutaneous nerve of the thigh accidentally (seatbelt injury from a car accident, for example), or inadvertently, during medical or surgical procedures (for example, laparoscopic (keyhole) hernia repairs) and treatments.

Rarer causes include a neuroma. Neuromas are benign (noncancerous) tumours (growths) on a nerve. Pelvic or intra-abdominal tumours (including cancerous ones) could also compress the nerve and cause this problem. This is rare. Other possible causes include lying down for long periods of time in a curled up position. Diabetes can affect nerves in general and, although it would be unusual simply to have this one nerve affected, the lateral cutaneous nerve of the thigh could potentially be damaged by diabetes.

Who gets meralgia paraesthetica?

Anyone can get meralgia paraesthetica and it affects men and women in equal numbers. Generally it occurs between the ages of 20 and 60, though it is at its most common in middle age, and is much rarer in children.

Risk factors include obesity, pregnancy and ascites (a tense swelling of the abdomen due to fluid).

How common is meralgia paraesthetica?

It is estimated that about 4 in 10,000 people per year develop meralgia paraesthetica. This makes it seem quite an uncommon condition. However, this reflects the number of new cases; there are always a greater number of people with the existing condition. GPs are used to seeing people with meralgia paraesthetica.

What are the symptoms of meralgia paraesthetica?

The most common symptoms are burning pain or numbness in the upper thigh, on the outer side. Children and younger people may just have pain that limits normal activities.

Other symptoms include altered sensation of that part of the thigh, or tingling/pins and needles. Symptoms tend to be made worse by walking and standing, but relieved by lying down with the hip flexed. (Hip flexion is movement of the leg towards your abdomen; this can be with your knee bent or straight - but on your back it is easiest to draw your bent knee up to your chest.)

Other reported symptoms include aching in the groin, pain in the buttocks and an area of skin that seems supersensitive to heat and light touch (as opposed to firm pressure).

How is meralgia paraesthetica diagnosed?

A doctor can make the diagnosis based on your symptoms and examination of your body. The diagnosis is likely to be suspected if you have typical pain or sensory symptoms affecting the upper outer thigh. The condition can, occasionally, affect both sides at the same time (about 1 in 5 cases).

Examination might show altered sensation in the area of skin supplied by the lateral cutaneous nerve of the thigh. The pain can usually be provoked by getting you to extend your hip. Hip extension is the movement of the leg backwards. The main buttock muscle (gluteus maximus) tightens when you make this movement.

Because the lateral cutaneous nerve of the thigh is a sensory nerve, it affects feeling and sensation. It does not affect movement of the leg or hip. Your doctor will check to see that there is no weakness of the muscles - if there is, the diagnosis is not meralgia paraesthetica.

Do I need any investigations?

No - investigations (such as blood tests, X-rays and scans) are not usually needed for the diagnosis of meralgia paraesthetica.

Occasionally, further tests may be done if an underlying problem or alternative diagnosis is suspected (but this is not usually the case). If you have meralgia paraesthetica arising from an accident or injury (say, a pelvic fracture), other tests could be expected.

In some cases, nerve conduction tests are performed if surgery for meralgia paraesthetica is planned. Nerve conduction tests look at the electrical activity running through a nerve. This is adversely affected if a nerve is compressed or trapped.

What is the treatment for meralgia paraesthetica?

Treatments can be grouped into conservative treatments (which are nonsurgical), and surgical treatment (operations). In most cases, only conservative treatments are needed.

Examples of conservative treatments include:

• Rest. Meralgia paraesthetica is aggravated by standing and walking. Reduction in physical activity, and sometimes even bed rest, may be advised in severe cases.
• Weight loss - if obesity is thought to be the cause.
• Analgesics (painkillers) - such as paracetamol or codeine.
• Non-steroidal anti-inflammatory drugs (NSAIDs) - such as ibuprofen, naproxen and diclofenac.
• Corticosteroid injections - commonly referred to as steroid injections. A steroid and, usually some local anaesthetic, can be injected around the lateral cutaneous nerve to numb it and reduce inflammation.
• Other medicines - sometimes medications are used that act as nerve painkillers. Some types of antidepressant medications (tricyclic antidepressants) such as amitriptyline or anticonvulsant drugs can be useful for nerve-related pain (also called neuralgia or neuropathic pain). Examples of these drugs include gabapentin (brand name Neurontin®), pregabalin (brand name Lyrica®) and carbamazepine (brand name Tegretol®).

If you have meralgia paraesthetica it is also advisable to avoid tight clothing that presses on the upper thigh/hip area - such as belts or corsets.

Surgical treatment involves taking the pressure off the nerve (surgical decompression) and releasing any entrapment.

What is the prognosis (outlook) for meralgia paraesthetica?

Generally, the prognosis is good. Often, the symptoms of pain and pins and needles resolve with time, but sometimes the numbness and altered sensation can remain, long-term. But, if there is a serious underlying cause of the entrapment (rare), the prognosis is less good.

References

• Sekul EA; Meralgia Paresthetica, eMedicine, Aug 2009