Contents
Introduction
Mononeuropathy of the lateral femoral cutaneous nerve (LFCN) which may cause pain, paresthesias, and sensory loss within the nerve distribution of lateral thigh.
History:
MP was first described by Hager in 1885 and eventually named by Roth in 1895. MP has also been referred to as Bernhardt‐Roth syndrome or LCN (lateral cutaneous nerve) neuralgia.
Anatomy
Lateral femoral cutaneous nerve (LFCN) or lateral cutaneous nerve (LCNT):
The LCNT is part of the lumbar plexus. It functions primarily as a sensory nerve and its composition varies among individuals with several different combinations of lumbar nerves that originate from L1 to L3. The LCNT then emerges at the lateral border of the psoas major, crosses the iliacus, to the anterior superior iliac spine. The nerve then passes under the inguinal ligament and over the sartorius muscle and enters the thigh as it divides into an anterior and posterior branch.
Anatomyical variations:
Aetiology
Risk factors:
- Diabetes mellitus
- Lead poisoning
- Alcoholism
- Hypothyroidism
Mechanical causes:
Due to pressure on the LFCN
- External direct pressure: Tight seat belts, belts, or restrictive clothing.
- Increased intra-abdominal pressure: Obesity, pregnancy, or tumors
- Leg length discrepancy
- Pubic symphysis degenerative defects
- Iliac crest bone tumor (near the anterior superior iliac spine)
Iatrogenic causes:
Due to surgical intervention or direct nerve injury
- Hip replacement surgery, spine surgery, laparoscopic inguinal repair, pelvic osteotomy, surgery in the area of the anterior superior iliac spine, iliac crest bone graft harvesting, acetabular fracture surgery, laparoscopic myomectomy, laparoscopic cholecystectomy, vein harvesting for coronary bypass surgeries, or bariatric surgery
Clinical features
Classically, meralgia paresthetica is described as a syndrome of dysesthesia or anesthesia in the distribution of the LFCN.
Anterolateral thigh dysesthesia:
Patients typically describe burning, coldness, lightning pain, deep muscle achiness, tingling, frank anesthesia, or local hair loss in the anterolateral thigh. The symptoms may be mild and resolve spontaneously or may severely limit the patient for many years.
Diagnosis
Diagnosis is based primarily on the history and physical exam, including purely sensory neurological changes without motor involvement in the anatomical location of the upper thigh. Evaluation should include a complete lower extremity neurologic examination. Deficiencies may be noted with pinprick and light touch over an approximately 10″ x 6” oval area over the anterolateral thigh, however, deficiencies may also be noted more anteriorly or medially based on a patient’s specific anatomy. A lower extremity neurologic exam is normal with preserved deep tendon reflexes, motor strength, negative straight leg raise, and without sacroiliac, back, or hip abnormalities
Pelvic compression test:
Patient lies on their unaffected side and the examiner applies downward pressure on the patient’s ilium/pelvis for approximately 45 seconds. Test is positive if symptoms are reduced
Neurodynamic testing:
Findings not associated with meralgia paresthetica include motor deficits, abnormal lower extremity reflexes, other sensory losses outside the LFCN distribution, or other neurologic symptoms.
Differential diagnosis:
During the differential diagnosis of lateral or anterolateral thigh pain, MP should be considered as a potential cause if the more common diagnoses such as an upper lumbar nerve root (L1‐L3) problem or trochanteric bursitis have been ruled out or if the individual has been refractory to treatment.
Frequently patients have been treated for presumed back, hip, and groin pathology before meralgia paresthetica is correctly diagnosed. Patients often find it difficult to describe their symptoms and may come to believe that their problem is psychiatric.
Management
Meralgia paresthetica is a typically benign and self-limited condition with frequent spontaneous remission. Treatment focuses on patient reassurance and ways to reduce pressure and irritation over the nerve and groin region.
Supportive management:
This includes patient education that the condition is benign, counseling the patient to avoid tight-fitting garments, and discussion of weight loss if obesity is a contributing factor.
- Icing: Reduce local nerve irritation and inflammation of acute symptoms.
- Abdominal exercises: Reduce pressure
Pharmacological management:
- NSAIDs, topical capsaicin, lidocaine, or tacrolimus (for epidermal dysesthesia or cutaneous hypersensitivity)
- Anticonvulsants (gabapentin, phenytoin, or carbamazepine): Treating neuropathic pain
- Nerve block injections: Local anesthetic, glucocorticoids
Surgical management:
Surgery is rare but may be considered in chronic refractory cases, and is performed via either a surgical release procedure with decompression of the LFCN (which may include transposition of the LFCN approximately 2cm medially away from ASIS) or via a nerve transection procedure. The nerve decompression procedure preserves sensory function but is generally less successful than the sectioning procedure, which results in permanent anesthesia and is reserved only for patients with intractable pain.
