A Burning Problem
According to the Trust For America’s Health, obesity is sweeping through our nation at an alarming rate. In their 2011 study released in July, Illinois ranked as the 23rd “fattest” state with an estimated 63.7% of the population considered either “overweight” or “obese”. The “leanest” state, Colorado, weighs in with “only” 15% of the population considered obese. In 1995, 15% obesity would have ranked it as the worst! Expanding waistlines lead to countless musculoskeletal problems including low back pain, hip, and knee osteoarthritis and my topic for this month- meralgia paresthetica.
Meralgia paresthetica (MP) is an often missed diagnosis for tingling, numbness, and burning pain on the anterolateral thigh. It is generally caused by a focal entrapment of the lateral femoral cutaneous nerve (LFCN), as it passes beneath the inguinal ligament. The LFCN is responsible for sensation to the anterolateral thigh, it is a purely sensory nerve and has no motor component.
The compressive lesion commonly includes the inguinal ligament, tensor fascia lata and/ or psoas. Pregnancy, prolonged seated postures, tight clothing, girdles, compressive garments, belts, and obesity predispose patients to compression of the nerve at the inguinal ligament. Carpenter’s tool belts or police duty belts may compress the LFCN. Lying in the fetal position for prolonged periods also has been implicated, as has prone positioning after lumbar spinal surgery. Meralgia paresthetica is more common in diabetics than in the general population. Rarely, MP has other etiologies such as a compressive neoplasm in the retroperitoneal space.
In the early stages, symptoms are mild and intermittent. Walking or standing may aggravate the symptoms; sitting tends to relieve them. In advanced stages, paresthesia develops into shooting pains that are unaffected by position change. Sensitivity to light touch is sometimes greater than sensitivity to deep pressure. Symptoms are typically unilateral although bilateral presentations are not uncommon.
Examination reveals numbness or hyperesthesia of the anterolateral thigh. Deep palpation or percussion of the upper and lateral aspects of the inguinal ligament, just below the ASIS, may reproduce or exacerbate the symptoms. Motor strength and reflexes in the involved leg should be normal.
A study in 45 patients found that the “pelvic compression test” had a sensitivity of 95% and a specificity of 93.3% for meralgia paresthetica (1). This test is based on the premise the LFCN is compressed by the inguinal ligament and that relieving this compression will alleviate symptoms. The test is performed with the patient in a side posture position and focusing on their symptoms while the examiner applies a downward and lateral compressive force on the upper iliac crest. By compressing the pelvis in this manner, the two attachments of the inguinal ligament are approximated causing the ligament to become less taut. The pressure is held for 45 seconds is the test is positive when the patient reports an alleviation of their symptoms.
Evaluation of hip flexibility and strength often reveals what Jull and Janda describe as a “pelvic crossed syndrome” in which there are hypertonic hip flexors, lumbar erector spinae, and hamstrings with associated weakened antagonists (gluteus maximus, medius and minimus, and abdominals).
The clinical syndrome is well defined, and further diagnostic studies may be unnecessary. However, in unresponsive cases, the diagnosis can be confirmed by nerve conduction studies. Advanced imaging is appropriate if a mass lesion in the retroperitoneal space is suspected, or if a lumbar radiculopathy is in the differential. Other differential diagnostic considerations for MP include trigger point referral patterns from the gluteus medius or TFL muscles.
The central goal of treatment is to remove any causes of excessive compression. In some cases, simply wearing looser clothing may alleviate the symptoms of meralgia paresthetica. Other considerations include: selective rest from an aggravating activity-particularly repetitive hip flexion, losing weight, or using a toolbox instead of wearing a tool belt. Electrotherapy with ice or pulsed ultrasound may be helpful to alleviate symptoms and to enable the provider to perform treatment and stretching with greater ease. Soft tissue manipulation including Active Release Technique (ART) may be applied to hip, thigh and spinal muscles, particularly the illiopsoas, TFL, and adductors. Caution should be used to avoid trauma to the exiting LFCN. Manipulation for a restricted lumbar segment or sacroiliac joint will promote better biomechanics. Post-isometric relaxation stretching of the hip flexors, psoas, TFL, hamstrings, and lumbar erectors is beneficial. Femoral nerve flossing may be useful. A home exercise program will include stretching of these affected muscles and strengthening exercises to address any hip or core stability issues. In exceptionally recalcitrant cases, injections or surgical intervention may be required.
- Nouraei SA, Anand B, Spink G, O’Neill KS. A novel approach to the diagnosis and management of meralgia paresthetica. Neurosurgery. Apr 2007;60(4):696-700; discussion 700. [Medline].