User:Snake playing a saxaphone/Meralgia paraesthetica

Also known as Bernhardt Roth syndrome, lateral femoral cutaneous nerve syndrome, lateral femoral cutaneous neuralgia.

MP can be diagnosed by primary care physicians, obstetricians/gynecologists, surgeons, urologists, and neurologists.

MP is caused by entrapment of the lateral femoral cutaneous nerve.

Anatomy
LFCN originates from the lumbar plexus and contains fibers from L2 and L3. [description of the course of nerve]

LFCN is a purely sensory nerve.

The site of compression is often at or near the inguinal ligament.

The LCNT emerges at the lateral border of the psoas major, crosses the iliacus, and continues to the anterior superior iliac spine. The nerve then passes under the inguinal ligament and over the sartorius muscle. It then divides into an anterior and posterior branch as it passes into the thigh.

Signs and symptoms
Pain, parasthesias, or dysthesias on the anterolateral surface of the thigh that extends just above the knee.

Symptoms exacerbated by standing or prolonged hip extension. Relief may be seen when sitting or flexing the hip.

Pressure on the skin may exacerbate symptoms.

Sometimes strenuous exercise may exacerbate symptoms.

Symptoms are typically unilateral, seen in about 78% of cases.

Symptoms are sensory since the LFCN does not contain motor fibers.

The symptom severity can be mild to severe that limits function.

Causes
Compression or injury to the LFCN.

Risk factors include tight fitting clothing at the waist, tight belts, or tight seat belts.

MP can be iatrogenic from peri-operative positioning or by spinal, pelvic, and abdominal operations.

MP can be due to accidents that injures the LFCN.

Conditions which increase intra-abdominal volume such as ascites, obesity, and pregnancy.

Having other compression neuropathies like carpal tunnel is a risk factor.

Mass lesion such as tumor or cyst anywhere along the course of the LFCN.

Pathophysiology
Anatomic variations in the course of the LFCN through the inguinal ligament, its branching level and course through the thigh is thought to predispose the LFCN to nerve damage.

Diagnosis
Diagnosis is generally based on clinical examination and patient history.

In typical cases an infiltration test is performed.

First rule out myofascial pain syndrome.

Some differential diagnoses include L2/L3 lumbar radiculopathy  , another entrapped peripheral nerve (e.g. femoral neuropathy)  , lumbar plexopathy , abdominal masses , and pelvic tumors.

A lumbar MRI can rule out lumbar radiculopathy.

Atypical presentations involve an extended workup that involves MRI neurography, electrophysiology testing, neurosonography.

Imaging like MRI/CT/x-ray can be used to rule out mass lesions (e.g. tumor) that could explain the symptoms.

MRN can be used to assess signal alterations along the LFCN.

Neurophysiological testing can include sensory nerve conduction studies or somatosensory evoked potentials.

A guided injection of anesthetic is used to confirm LFCN involvement and distinguish it from lumbosacral root pain. The nerve block test of the LFCN is considered positive if the patient has immediate symptom relief lasting 30-40 minutes after the injection.

Common differential diagnoses are lumbar stenosis, disc herniation, and nerve root radiculopathy.

Treatment
MP is typically a self-limiting condition with spontaneous remission. In one study evaluating the natural history of MP, 62% of patients with no treatment had complete symptom resolution after 2 years.

If repeated infiltations lead to medium/long-term improvement, then conservative therapy is recommended. If repeated infiltrations do not lead to symptom improvement, then surgery is recommended.

Conservative
Conservative therapy seeks to reduce aggravating factors. This includes eliminating tight fitting clothing and tight belts, losing weight, physical therapy to stretch the muscles and tendons present along the course of the LFCN.

Guided injections can also be used therapeutically especially if combined with an corticosteroids. The relief from steroid injections is highly variable, with long-term, complete pain relief of approximately 22%. The revision rate for injections is approximately 81% and a revision is likely to either be a repeat injection or a nerve decompression.

Medications can be used for symptomatic treatment. Examples include NSAIDs, topical capsaicin, and lidocaine for epidermal hypersensitivity or dysthesias.

Surgical
Good success rates have been seen with a nerve decompression and neurectomy.

The benefit of a nerve decompression is that it keeps the LFCN intact which preserves sensation.

With a neuroectomy, there will be permanent numbness distal to the site of transaction. In studies measuring patient quality of life find that patients are rarely bothered by the loss of sensation.

Nerve decompression is generally less successful than neurectomy although both are effective. In a systematic review, complete pain relief was also seen in 85% of neurectomy cases and 63% of decompression cases. A Cochrane review found that decompression led to relief in 60%-99% of patients and neurectomy led to relief in 85%-100% of patients.

The revision rate for nerve decompression is 12% and a revision was either a repeat decompression or neurolysis. The revision rate for neurolysis is approximately 0%.

One systematic review found that the complication rate after neurectomy is 0%, and after neurolysis is 5%. The most common complications after decompression or neurectomy is hematomas, subcutaneous effusions, wound healing disorders, and wound infections.

Emerging treatments include radiofrequency ablation to destroy the LFCN.

Epidemiology
Incidence is 32-43 cases per 100k people per year. There is an association between MP and age, BMI, and diabetes mellitus. In 68% of cases MP occurs in middle-aged men.

History
MP was first described in 1885 by Martin Bernhardt and named by Vladimir Karlovich Roth in 1895. Roth noticed it in cavalrymen who wore their belts too tightly. Consequently, MP is also known as Bernhardt-Roth syndrome.