Date: 26th January 2012
Meralgia Paraesthetica - a common presentation
Meralgia paraesthetica (MP) is a relatively common diagnosis in a Neuro/Orthopaedic surgical or Neurological clinic. These patients are often incorrectly referred as a painful radiculopathy i.e. pinched nerve in the lumbar spine - femoralgia. However, they are totally different conditions. In MP it is the lateral femoral cutaneous nerve (LFCN) of the thigh that is entrapped as it passes through the inguinal ligament medial and/or inferior to the anterior superior iliac spine. These patients with MP present with burning, sensory symptoms in the outer thigh. The LFCN is a purely sensory nerve so there is no motor weakness or depression of the knee reflex. The LFCN arises directly from the lumbar plexus and has root innervation from L2/3. The nerve runs through the pelvis along the lateral psoas muscle to the lateral part of the inguinal ligament. At this site, it enters the thigh compartment through a tunnel formed by the attachment of the inguinal ligament and the anterior superior iliac spine. It is at the entry into the thigh under the fascia larter that the nerve is most susceptible to entrapment. This is usually 1 centimetre medial to the ASIS.
MP is more common in diabetics with obesity and it can be bilateral in 20% of cases. The burning pain and paraesthesiae in the lateral thigh forms the description "meralgia paraesthetica". On examination, the patients have numbness in the outer thigh and tapping over the inguinal ligament or extending the thigh may reproduce the symptoms. Motor strength and reflex examination of the knee should be normal.
Causes include: obesity, pregnancy, tight clothing (in the US it is called Levi Jeans syndrome), tool belts worn by carpenters, duty belts worn by police and security guards and being in a prolonged foetal position. It is much more common in diabetics. Rare causes include masses such as haemorrhages in the iliopsoas muscle.
The differential diagnosis includes a painful lumbar radiculopathy eg L3 nerve root compression by a lateral L3/4 disc protrusion or a femoral neuropathy. MRI and electrophysiology including EMG may be helpful. An EMG may show denervation which would suggest a lumbar radiculopathy i.e. femoralgia.
The treatment for MP is multi-factorial. Weight loss, wearing loose clothing, a short course of diuretics/steroids/agents such as Endep or neuropathic agents may help. Injection of anaesthetic and steroid, medial to the ASIS, may be beneficial for an extended period of time. In rare cases, not responsive to simple measures and with a predominance of meralgia (the pain) over paraesthetica (pins and needles sensations) may be successful. The nerve is thin and friable and surgical success rate is not as high as it is for conditions such as carpal tunnel syndrome, ulna neuropathy etc.