What is the cause of pain over the iliac crest and left lateral/anterior hip with numbness over the anterior thigh?

Meralgia Paresthetica (Lateral Femoral Cutaneous Nerve Entrapment)

The clinical presentation of pain over the iliac crest and left lateral/anterior hip with numbness over the anterior thigh is diagnostic of meralgia paresthetica, an entrapment neuropathy of the lateral femoral cutaneous nerve (LFCN). 1

Clinical Diagnosis

The symptom complex you describe is pathognomonic for LFCN compression:

• Numbness, paresthesias, and pain in the anterolateral thigh are the hallmark features that differentiate this from other neurologic disorders 1
• The pain distribution over the iliac crest and anterior hip with anterior thigh numbness follows the exact anatomic course of the LFCN as it exits the pelvis near the anterior superior iliac spine 1, 2
• No motor deficits occur because the LFCN is purely sensory 1

Anatomic Basis

The LFCN is highly susceptible to compression at specific anatomic sites:

• Most common site of injury is where the nerve exits the pelvis near the anterior superior iliac spine and passes under or through the inguinal ligament 1, 3
• The regional anatomy of the LFCN demonstrates high variability, which accounts for its susceptibility to local trauma 1, 3
• Compression can occur throughout the nerve's entire course from the lumbar plexus to its cutaneous distribution 1

Common Etiologies to Identify

Mechanical compression is the most frequent cause:

• Tight clothing, belts, or external compression devices worn around the waist 2
• Obesity and diabetes mellitus are predisposing factors 1, 4
• Pregnancy due to increased abdominal girth 3
• Prolonged positioning (prone positioning during spine surgery has been implicated) 4

Iatrogenic causes must be excluded:

• Prior iliac crest bone graft harvesting 1, 3
• Previous pelvic or spine surgery 1, 4
• Anterior pelvic procedures 1

Critical Diagnostic Pitfall

Meralgia paresthetica can mimic low-back pain and radiculopathy because of symptom similarity, leading to unnecessary spine workup 2. However, the key distinguishing features are:

• Absence of back pain radiation following dermatomal patterns 2
• Normal straight leg raise and neurologic examination of lower extremity motor function 1
• Symptoms isolated to the anterolateral thigh without posterior thigh or leg involvement 1

Diagnostic Confirmation

Diagnostic nerve block is both confirmatory and therapeutic:

• Injection of local anesthetic (10 mL of 0.25% bupivacaine) at the site of nerve compression provides immediate pain relief and confirms the diagnosis 2
• If no improvement occurs after injection, proximal LFCN irritation or alternative diagnoses should be sought 1

Red Flag: Exclude Malignancy

Although rare, retroperitoneal neoplasms or malignant deposits in the iliac crest can present identically to meralgia paresthetica 5. Consider imaging if:

• Patient has constitutional symptoms (weight loss, night sweats) 5
• History of malignancy 5
• Symptoms are progressive despite conservative management 5
• Age >50 with new-onset symptoms 5

Treatment Algorithm

First-line conservative management (4-6 weeks):

• Remove all compressive agents (tight belts, clothing) 1, 2
• NSAIDs for pain control and anti-inflammatory effect 1, 2
• Activity modification and relative rest 2

Second-line intervention if symptoms persist:

• Local corticosteroid injection at the site of nerve entrapment 1
• This provides both diagnostic confirmation and therapeutic benefit 1

Surgical consideration only for intractable pain:

• Reserved for cases failing all conservative measures 1
• Controversy exists between neurolysis versus nerve transection 1
• Nonoperative management usually results in satisfactory outcomes 1