The most common cause of numbness of the thigh is due to a condition called meralgia paraesthetica.
Meralgia paraesthetica is a condition that is characterized by symptoms such as numbness, tingling and burning pain involving the outer thigh. This occurs due to compression of the lateral femoral cutaneous nerve, also simply known as the lateral femoral nerve, that supplies sensation to the surface of the skin of the thigh.
The symptoms of meralgia paraesthetica include the following:
- Numbness and tingling over the lateral (outer) part of the thigh.
- Burning pain on the surface of or in the lateral part of the thigh.
The most common causes of this condition includes any that results in compression of or damage to the lateral femoral cutaneous nerve.
Conditions or situations that result in increased pressure on the groin include:
- Tight clothing including corsets, tight pants, normal belts and utility belts.
- Weight gain or obesity.
- Injury or past surgery resulting in scar tissue formation near the inguinal canal or ligament.
Nerve injury or damage can be caused by the following:
- Diabetes - increased glucose levels in the blood stream causes damage to the walls of the arteries which results in narrowing of these vessels. This leads to decreased blood flow and therefore decreased supply of oxygen and nutrients to the nerves, which results in them becoming damaged.
- A seat belt injury after a motor vehicle accident can also damage the lateral femoral cutaneous nerve.
In the majority of cases, doctors can make a diagnosis of meralgia paraesthetica based on the patient's medical history and from clinical observation when examining the patient.
Further investigations can be performed to help rule out other conditions. These include:
- X-rays of the hips and pelvic area.
- Electromyography is performed to measure the electrical activity in muscles. This test is normal in meralgia paraesthetica, but may be needed to rule out other conditions when the diagnosis isn't clear.
- Nerve conduction studies are done to help diagnose injured nerves.
- Nerve blockade is done by injecting an anaesthetic medication into the thigh, where the lateral femoral cutaneous nerve enters into it, using ultrasound guidance. If pain relief is experienced, then meralgia paraesthetica can be confirmed.
The pain caused by this condition can resolve within a few months by managing this problem through conservative measures, which include the following:
- Losing weight.
- Wearing clothing that isn't tight.
- Taking over-the-counter (OTC) medications such as acetaminophen or ibruprofen for pain relief.
If the symptoms of this condition carry on for two or more months, or the pain is severe, then treatment may include the following measures:
- Injecting steroid medications around the nerve to reduce inflammation and allow for temporary pain relief.
- The patient can have tricyclic antidepressants prescribed which can relieve pain by working on the nerves directly.
- Other medications that can be prescribed, and that function similarly to the tricyclic antidepressants, include anti-seizure drugs such as gabapentin, phenytoin or pregabalin.
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