Meralgia paresthetica (MP) is a painful mononeuropathy of the lateral femoral cutaneous nerve (LFCN)2,3). It occurs following entrapment of LFCN as it exits the pelvis and pierces the inguinal ligament2). It is usually reported in patients sustaining trauma to the inguinal ligament, individuals assuming squatting postures for prolonged periods, and in cases involving leg-length discrepancies, with the pelvic-tilt stretching the fascia lata and consequently the nerve against the entrapment point2,6). Although pregnancy and obesity-associated pannus are the most common scenarios, tight-clothing, belt holsters, iliac bone graft harvest, and entrapment from surgical scarring have all been implicated2,3,6). Pain and paresthesia, which may progress to numbness of the upper lateral thigh, are the key features of MP2).

In the classic form of MP, the symptoms are fairly stereotypical and the clinical diagnosis is fairly straightforward7,9). However, a diagnosis of MP is not always straightforward in clinical practice7,9). This condition can be easily confused with lumbosacral radicular pain in a small group of patients7,9). In the current case, the diagnosis of MP was fairly delayed by coexisting symptoms of lumbar disc herniation.

A 49-year-old right-handed female patient presented with a 2-year history of gradually worsening pain and paresthesias, in her left buttock, anterior thigh, and leg. Two years ago, the patient was afflicted with sudden pain in her left lateral buttock and posterior thigh without any precipitating event. Since then, left-sided buttock and leg radiating pain occurred intermittently after a prolonged period of standing and working once or twice a month. The pain was relieved with over-the-count medications and bed rest within 2 weeks. One year prior to the recent presentation, sudden, aching pain and paresthesia developed in her left groin and radiated to anterior and lateral thigh. The pain in her left groin, buttock and lateral and posterior thigh developed during standing for more than 30 min. She was diagnosed with lumbar disc herniation at L4/5 after magnetic resonance imaging (MRI) of the lumbar spine. She was treated conservatively with regular medication and physical therapy. However, her pain in the left buttock and posterolateral thigh failed to improve and worsened gradually. She visited our outpatient clinic for further evaluation and treatment.

She complained of recurrent episodes involving her left buttock and radiating pain in her left anterior thigh. Back and anterior thigh pain prevented the patient from work for 1 week. Physical examination revealed no tenderness or limitation of back motion. No objective signs of motor or sensory abnormality was detected in the physical examinations. The pain in the buttock was described as mainly dull aching with moderate severity (4-5/10 on numerical rating scale; range, 0-10). It was aggravated with prolonged standing or walking for more than 20 min. Straight leg raise was mildly restricted in the left leg (80/60). Deep tendon reflex was normal. Laboratory examinations were normal, including erythrocyte sedimentation rate and C-reactive protein. MRI of the lumbar spine revealed a left-sided herniated disc at the level of L4/5 (Fig. 1A). Lumbar epidural blocks were performed twice considering the possibility of lumbar disc herniation. Two weeks after epidural blocks, the patient reported pain improvement of left buttock and posterior thigh. However, her pain and paresthesia in her anterior thigh did not improve and, even, deteriorated despite pain relief in the buttock. Additional history and physical examination were considered. Indeed, the patient had already reported pain and paresthesia in her left anterior thigh in addition to posterior thigh pain during the first interview at the outpatient clinic. However, we failed to understand the importance of anterolateral thigh pain.

Her groin pain originated in her left inguinal area and radiated to anterior thigh. It also radiated to left lower quadrant of the abdomen. A mild tenderness was noted in her left inguinal area around left anterior superior iliac spine (ASIS) (Fig. 1B). Tinel’s sign was positive. Burning dysesthesia and paresthesia in her anterior thigh were described. No objective signs of sensory abnormality was detected. A diagnostic block of the LFCN with 5 mL of 1% lidocaine was effective for 6 hr. Decompression of the LFCN was proposed due to chronicity and medical intractability of MP. Three-dimensional computed tomographic (CT) scan and MRI of the pelvis showed no mass lesion or anatomical abnormality in the left inguinal area.

An approximately 6-cm skin incision was created below the ASIS over the course of left inguinal ligament, down to the fascia lata. The LFCN was carefully identified from the Sartorius muscle and decompressed distally by opening the fascia lata (Fig. 2A)2,3). It was then followed proximally, and the entrapment point was found in the inguinal ligament and tendinous arc from the iliac fascia (Fig. 2B). The portion of the inguinal ligament and tendinous arc of the iliac fascia abutting the LFCN were divided, freeing the LFCN (Fig. 2C). Immediately following decompression of the left LFCN, no repeated attacks of pain in the left inguinal and anterior thigh occurred. No sensory abnormality, pain or paresthesia in her left groin and thigh was reported until 12 month follow-up.

The authors report a rare occurrence of MP associated with lumbar disc herniation. The diagnosis of MP is typically delayed by the coexistence of symptoms of lumbar disc herniation in addition to MP. Complaints of pain and paresthesia in the anterior and lateral thigh warrant investigation for possible MP, a rare painful mononeuropathy involving the LFCN.