Meralgia Paresthetica

Meralgia Paresthetica is a painful compressive neuropathy of the lateral femoral cutaneous nerve (LFCN), causing “burning” pain and paresthesia in the thigh.  (1-3) 

The LFCN is a pure sensory nerve, supplying a large area of skin on the anterior lateral thigh.  (1) The fibers comprising the LFCN originate from the L2 and L3 nerve roots before converging in the lumbar plexus.  The LFCN splits directly from the lumbar plexus, then runs through the pelvis, adjacent to the lateral border of the iliopsoas muscle, before passing beneath the lateral aspect of the inguinal ligament near the ASIS.  (4) The most common site of entrapment is beneath the inguinal ligament, as the nerve emerges onto the thigh.  (1,4) In some instances, the nerve may be compressed more distally as it passes through the sartorius or tensor fascia lata muscles.  (2)

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Demographics

Meralgia paresthetica may occur at any age but is most common in middle-aged adults.  (5,6) Diabetics have a nearly six-fold increased risk of developing the condition.  (7-9) It does not appear there is a predilection for one side or the other.  (10) The condition is present bilaterally in 20-25% of cases.  (5,10-12) The condition affects men up to three times more frequently than women.  (8,10-12)

Excessive compression or ischemic stretch of the LFCN is a primary etiological factor.  (1,3) The increased risk in males is possibly due to occupational risks, including carpentry tool belts, police duty belts, and soldier body armor.  (14,15) Other known sources of compression include excessively tight clothing, pregnancy, and obesity (BMI greater than 30).  (10,16-21) Recent weight gain often precedes the condition.  In fact, 8% of new cases report recent weight gains of more than 15 pounds.  (10,22) The LFCN suffers a similar fate from tight-fitting clothing, jeans, belts, or body-shaping undergarments.  Direct trauma, including seat belt compression, has been identified as another potential etiology.  (23-25) Spending extended periods of time lying in a prone position on a hard surface (i.e. surgery) may trigger the problem.  (26) Athletes who participate in gymnastics, baseball, soccer, bodybuilding, or strenuous exercise may be predisposed.  (27-31) Biomechanical factors, including excessive anterior pelvic tilt or leg length inequality, may be contributors.  (32,33)

Symptoms

The typical presentation includes a middle-aged patient with one or more of the aforementioned risk factors, complaining of isolated pain or paresthesia on the outside of the thigh.  (1,3) The pain is described with some variability, including dull, aching, itching, buzzing or burning, and may range from mildly uncomfortable to disabling.  (3,34-40) Complaints commonly include paresthesias or hypersensitivity.  (3) Symptoms may impair function and sleep.  (3,41) Complaints are often provoked by walking and alleviated when sitting, because sitting may decrease tension on the inguinal ligament. (11,12,41,42) Wearing tight clothing or belts will likely exacerbate the condition.

Clinicians should perform a thorough review of systems, with particular emphasis on diabetic risk factors, including a family history of diabetes: hypertension; age; gender; ethnicity; physical activity level; exertional shortness of breath; BMI; and frequent thirst.  (43)

Clinical Evaluation

Clinical evaluation will demonstrate tenderness to palpation over the lateral inguinal ligament in greater than 75% of cases.  (44)  The primary site of tenderness is the emergence of the LFCN, approximately one to two finger widths inferior and medial to the ASIS.  (44) Symptoms are usually provoked by hip or lumbar extension and relieved by flexion.  (11,12,41,42) Likewise, Yeoman and Nachlas tests may reproduce the patient’s symptoms.  Tinel’s sign may be present. Clinicians should assess for possible hypertonicity in the iliopsoas, tensor fascia lata, and sartorius.  (32) Joint dysfunction in the lumbar, sacroiliac and hip regions may coexist. Functional evaluation should include assessment for leg length inequality, lower crossed syndrome, or paradoxical breathing.

A study of 45 patients found the “pelvic compression test” had a sensitivity of 95% and a specificity of 93.3% for meralgia paresthetica (45). 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 his or her 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, and the test is positive if the patient reports alleviation of the symptoms.

Neuro Evaluation

Neurologic evaluation of the lower extremity may demonstrate numbness or hyperesthesia over the distribution of the LFCN.  (41) Since the LFCN is purely a sensory nerve, motor or reflex changes would suggest alternate pathology (i.e. lumbar disc lesion). (1) Clinicians may assess neurodynamic flexibility of the LFCN, with the patient in a side-lying position, affected side up, knee bent to 90 degrees, while the clinician extends and adducts the patient’s hip (LFCN Neurodynamic Test).  (46,47) 

The clinical syndrome of meralgia parasthetica is well-defined, and further diagnostic studies may be unnecessary.  (1,42) In unresponsive cases, the diagnosis can be confirmed by NCS, which is considered the gold standard.  (49,50) Advanced imaging is appropriate if a mass or lesion in the retroperitoneal space is suspected or if lumbar radiculopathy is in the differential. 

Other differential diagnostic conditions for meralgia paresthetica include trigger point referral patterns (from the gluteus medius or TFL muscles); retroperitoneal, abdominal, or pelvic pathology; lumbar disc lesion; or diabetes.  (51)

Treatment

Conservative management is the frontline treatment for meralgia paresthetica and is successful in up to 91% of cases.  (16,52,53) The central goal of treatment is to remove any cause of excessive compression.  (16,52) In some cases, simply wearing looser clothing may alleviate the complaint. Other considerations include selective rest from aggravating activity (particularly repetitive hip flexion), losing weight, or carrying a toolbox instead of wearing a tool belt. Wearing high heels should be avoided, as this causes excessive anterior pelvic tilt, which may be linked to the problem.  (32)

Myofascial release and stretching may be appropriate for tightness in the hip flexors, sartorius, TFL, quadriceps, and thigh adductors.  (52-57) Clinicians may choose to perform nerve mobilization and/or IASTM; however, clinicians must be judicious in the application of these techniques to avoid excessive trauma or ischemic compression of the LFCN.  Stabilization exercises are appropriate for the core and pelvis.  (53-57) One small study demonstrated significant improvement in meralgia paresthetica symptoms following the application of therapeutic exercise tape.  (60,61)

Patients may consider ice, over-the-counter analgesics, and NSAIDs for symptomatic relief.  (62) Severe or recalcitrant cases may benefit from anesthetic block or local steroid injection.  (63-65) Surgical intervention should be reserved for those who fail all other forms of conservative management.  (62) High success rates have been associated with surgical decompression (88%) and LCFN nerve resection (94%).  (62,66)

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