Meralgia Paraesthetica

Meralgia paraesthetica comes from the Greek words meros (thigh) and algos, (pain).¹ Meralgia paraesthetica is usually an entrapment syndrome of the lateral femoral nerve. It may be iatrogenic after medical or surgical procedures, or result from a neuroma. The segmental origin is L2,3 and it is a purely sensory nerve with no motor fibres.²

It is said to be comparatively common in adults but much rarer in children. A study of 20 cases in children and adolescents found that half the patients had bilateral lesions.³

Risk factors^2,4

No gender proclivity is known. It may be bilateral. It can occur in pregnancy, obesity, and if there is tense ascites.⁵ It may be a result of trauma, previous surgery or in some cases may arise from abduction splints used to treat Perthes' disease, also called Legg-Calve-Perthes disease. Risk factors can arise in the most unlikely scenarios. Recently, a spate of meralgia was found to be due to the body armour worn by American soliders in Iraq.⁶ Most cases are idiopathic.

Entrapment causes burning or numbness down the upper lateral aspect of the thigh. In children and adolescents the presentation is severe pain causing marked restriction of activities.³

The pain can be reproduced by deep palpation just below the anterior superior iliac spine (pelvic compression) and also by extension of the hip.⁸ There is altered sensation over the antero-lateral aspect of the thigh. There is no motor weakness.

Very often the diagnosis is slow to be made. Pain in the lateral thigh can arise from the back, hip or knee.⁹ It is important to consider the possibility of the diagnosis and to try deep palpation medial to the anterior superior iliac spine and extension of the hip. Injection with local anaesthetic appears to be a good test.
Other conditions that may need to be ruled out include:⁷

• Diabetic lumbosacral plexopathy
• Lumbar degenerative disk disease
• Lumbar facet arthropathy
• Lumbar spondylolysis and spondylolisthesis
• Mononeuritis multiplex
• Neoplastic lumbosacral plexopathy

• The pelvic compression test is highly sensitive, and the diagnosis can often be made with this test alone.⁸
• Injection of the nerve with local anaesthetic will abolish the pain. Find the spot where deep pressure reproduces the pain and infiltrate below there. The nerve is quite superficial.
• Nerve conduction studies may be used before operation.¹⁰

Other tests to rule out differential diagnoses might include fasting blood glucose, MRI of the lumbar spine and radiographs for possible pelvic fracture or cancer.

In the case of obesity, loss of weight may cure the condition but is not guaranteed. It should resolve after pregnancy and tapping of ascites should help. Idiopathic meralgia paraesthetica usually improves with nonoperative modalities, such as removal of compressive agents, nonsteroidal anti-inflammatory drugs, and, if necessary, local corticosteroid injections.¹¹ If the pain is severe, operative decompression should be considered.

The nerve originates from the L2,3 segments and travels down, lateral to the psoas muscle. It crosses the iliacus muscle deep to the fascia and then passes through or under the lateral part of the inguinal ligament. It runs superficially and divides into anterior and posterior branches to innervate the lateral thigh. The course of the nerve can be a little variable but usually it can be found about 10 to 15 mm medial to the anterior superior iliac spine but can occasionally be up to 5 cm medial.¹²