What is meralgia paraesthetica?
Meralgia paraesthetica (US spelling, paresthetica) describes a localised form of cutaneous dysaesthesia in which there is pain and a changed sensation in the skin on the lateral aspect of the thigh.
Meralgia means pain in the thigh, and paraesthetica refers to burning pain, tingling or itch. Some patients describe itch in the affected area. Meralgia paraesthetica is also called lateral femoral nerve entrapment syndrome.
The patient often complains of intense itch but no rash; however, scratching and rubbing can cause bruises and thickened skin.
Meralgia paraesthetica causing lichen simplex
What is the cause of meralgia paraesthetica?
Meralgia paraesthetica is due to compression or traction of the lateral femoral cutaneous nerve in its pathway from the lumbar plexus, L2-3. This most often occurs under the inguinal ligament and may be precipitated by:
- Stretch injury, including after poor positioning after spinal, pelvic or hip surgery
- Scar tissue after surgery or trauma
- Tight clothing, belts and armour
- Items in a pocket resulting in a prolonged or repeated compression
- A pelvic tumour
- Small fibre neuropathy, such as in diabetes.
What are the clinical features of meralgia paraesthetica?
Meralgia paraesthetica is characterised by tingling, numbness, burning pain or rarely, intense itch (pruritus) on the outside of the thigh. In about one in five people, it can affect both sides. Symptoms can be intermittent or continuous. They tend to be made worse by standing and walking and relieved by sitting. When itchy, the itch is unrelieved by scratching, although the scratching and rubbing may be pleasurable.
In many patients, there are no visible signs. If it is itchy, visible changes often arise from rubbing and scratching the affected area. These include:
- Scratch marks
- Hyperpigmentation (brown marks)
- Hypopigmentation (white marks)
- Lichen simplex (a type of eczema)
There may be changed sensation in the affected area of skin, when this is tested for with pinprick, cotton wool or heat and cold, with either numbness or exaggerated sensations being reported. There may be reduced or absent sweating in the affected area.
What investigations may be performed in meralgia paraesthetica?
The examination should include extending the thigh posteriorly, as symptoms may be reproduced by stretching the nerve. The pelvic compression test is usually positive (this involves deep palpation in the groin). There should be no signs of muscle weakness.
Radiology such as ultrasound imaging, X-ray, CT scan or MRI of the hip and pelvic area may be recommended. In many cases, no abnormality is revealed. Other tests may include electromyography (EMG) and nerve conduction study to identify damaged nerves. The diagnosis may be confirmed by relief of symptoms after an injection of local anaesthetic into the entrapment site.
Skin biopsy is rarely performed and may show reduced intraepidermal nerve fibre density.
What is the treatment for meralgia paraesthetica?
Treatment of meralgia paraesthetica is not always necessary, as symptoms can settle on their own, and it is not always successful.
- Avoid wearing tight clothing.
- If obese, try to lose weight.
- If painful, medication such as paracetamol or ibuprofen may help.
- If itchy, apply cooling lotions or creams as required (camphor and menthol).
- If itchy, topical steroids are prescribed to treat associated lichen simplex.
- Local anaesthetic creams may provide temporary relief of symptoms if they are mild and superficial.
- Corticosteroid injection into the inguinal ligament may reduce swelling and pain.
- Local nerve block at the inguinal ligament may provide temporary relief of pain.
- Amitriptyline or other oral tricyclic at night may help sleep and counteract neuropathic symptoms.
- Gabapentin, pregabalin or other anticonvulsant are sometimes prescribed.
- Pulsed radiofrequency to the lateral femoral cutaneous nerve has been reported.
- Ultrasound-guided lateral femoral cutaneous nerve neurolysis has been reported.
- Surgical decompression of the pinched nerve may be undertaken in severe cases.
Physical therapy has been reported to be effective.