Meralgia paraesthetica is a pain condition which is relatively common but not well recognised and which gives pain, numbness and tingling in the front and outer side of the thigh. Described many years ago in the 19th century, it was soon deduced that this syndrome was due to compression of a nerve in the nearby area, the lateral cutaneous nerve of the thigh. This nerve is a sensory nerve which transmits feelings and has no muscular activation powers, supplying the feeling in the described areas of the thigh. The frequency of this condition is not clear but it does not appear to be common, however it may be under diagnosed.
This condition can be mistaken for a series of other musculoskeletal conditions such as nerve root compression, referred spinal pain and trochanteric bursitis and may be bilateral at times. The most common cause of this syndrome is inappropriate pressure on the on the nerve at particular points where it can be trapped. Being overweight may be a risk factor for this condition and it has been recorded as being caused by a tight belt. Various surgical procedures can be aggravating factors such as hip replacement, bone grafting and surgery to the quadriceps.
The lateral femoral cutaneous nerve is liable to being compressed at various sites along its length, emerging initially from within the psoas muscle, running beneath a ligament called the inguinal ligament, round the bony prominence at the top and side of the anterior pelvis and exiting into the leg through the firm connective tissue layer known as the fascia lata. The commonest type of nerve injury is a neurapraxia, the least serious, where the nerve responds to the compression by the loss of some of the insulating sheath or myelin sheath.
In a neurapraxia the nerve axon itself is not damaged and this grade of injury is one which recovers completely over a relatively short period up to a few months. If the axon tube itself is disrupted then the injury is classified as an axonotmesis, with the length of nerve axon degenerating all the way up to its cell body. Regeneration from this point is extremely slow leading to a very long period the patient has to wait if the injury is to resolve over time. A nerve which has been severely injured so the cut ends do no longer contact each other has no likelihood of showing any recovery unless surgery is employed.
During the examination the patient should be questioned about the occurrence of any injuries which could have contributed to their problems. The physical examination should record an altered ability to feel skin sensations on the lateral and anterior parts of the thigh with symptoms such as numbness, burning pain, pins and needles and reduced sensation. Typically symptom onset is insidious, coming on slowly at an initially low level and not referring further than knee level. Pain can vary from a dull aching to the more recognisable burning and sharp sensations. Symptom area can be variable depending on how severe it is.
The initial goal of treatment is to establish where and what the problem of compression is likely to be, as correcting a tight belt, fitted clothing or heavy objects carried on the waist can be a useful first strategy. Loss of weight in obese patients can be sufficient to change things so that some symptom resolution is achieved. The ergonomics of work may also be important to eliminate obviously risky postures or movements. A doctor may give corticosteroids or anaesthetic drugs by local injection to limit the inflammatory changes or break the pain cycles.
The lateral cutaneous nerve of the thigh can vary considerably in its anatomical course so any injections and surgery have to take account of these potential variations. Once the compression has been released the nerve tends to recover spontaneously. Injections can be considered if activity modification does not help, and surgery if all else fails with techniques including neurolysis which is nerve destruction by chemical injection or by other means. The nerve can also be cut or can be decompressed at the various potential compressive sites in the pelvis and thigh. Reports on groups of patients undergoing surgery have generally shown positive results.
