What is the diagnosis for left upper lateral thigh pain?

Diagnosis of Left Upper Lateral Thigh Pain

The most likely diagnosis is meralgia paresthetica, an entrapment neuropathy of the lateral femoral cutaneous nerve (LFCN) at the inguinal ligament, which presents as burning pain, dysesthesias, and numbness specifically on the anterolateral thigh. 1, 2, 3

Primary Differential Diagnoses to Consider

Meralgia Paresthetica (Most Likely)

• Burning pain and dysesthesias localized to the lateral thigh without gluteal involvement distinguish this from radiculopathy 1
• The LFCN (L2-L3) becomes entrapped at the inguinal ligament near the anterior superior iliac spine, though entrapment can rarely occur at the fascia lata level 2, 4
• Risk factors include diabetes, prolonged pressure from tight belts or clothing, weight gain, leg length discrepancies, prolonged standing, and trunk hyperextension 1, 2, 5
• Symptoms typically worsen with walking or prolonged standing and may improve with weight loss or removing the underlying cause 2
• This condition can mimic low-back pain and must be distinguished from lumbar radiculopathy 6

Lumbar Spine Pathology with Referred Pain

• L5 nerve root compression causes dorsal foot and big toe sensory loss with foot drop, not isolated lateral thigh pain 1
• True radiculopathy produces radiation below the knee into specific dermatomal patterns, unlike meralgia paresthetica which remains above the knee 1
• Screening the lumbar spine is mandatory in all cases of lateral thigh pain to rule out referred pain 7, 1
• Pain from upper lumbar facet joints (L1-L3) can refer to the flank, hip, and upper lateral thigh 7

Hip Pathology with Referred Pain

• Femoroacetabular impingement, labral tears, or osteoarthritis can refer pain to the lateral hip and thigh 1
• Hip pathology typically presents with groin pain as the primary complaint, though lateral radiation can occur 8, 1

Gluteal Muscle Trigger Points

• Active trigger points in gluteal muscles produce lateral leg pain patterns that can mimic radiculopathy and cross multiple dermatomas 1

Diagnostic Algorithm

Step 1: Clinical Assessment

• Identify the exact pain distribution: meralgia paresthetica remains confined to the anterolateral thigh above the knee without gluteal involvement 1, 2
• Assess for burning quality, dysesthesias, and numbness rather than sharp lancinating pain 2, 3
• Inquire about tight belts, recent weight gain, diabetes, prolonged standing, and leg length discrepancies 1, 2, 5

Step 2: Physical Examination

• Test pinprick and light touch sensation over the anterolateral thigh to document sensory loss 1, 2
• Palpate for tenderness at the anterior superior iliac spine where the LFCN passes under the inguinal ligament 2, 3
• Perform hip range of motion and FADIR test to exclude intra-articular hip pathology 8, 1
• Examine the lumbar spine systematically, as this is a common source of referred pain 1, 9

Step 3: Imaging Protocol

• If hip pathology is suspected, obtain AP pelvis and lateral femoral head-neck radiographs first 1, 9
• Radiographs assess for hip osteoarthritis, femoroacetabular impingement, stress fractures, and bone lesions 1
• MRI without contrast is required if radiographs are normal but clinical suspicion for hip pathology or stress fracture remains high 1
• Ultrasound imaging can confirm meralgia paresthetica by demonstrating a hypoechoic and swollen LFCN at the inguinal ligament 2

Step 4: Electrodiagnostic Studies (If Needed)

• Sensory nerve conduction velocity studies of the LFCN are useful when the diagnosis is uncertain, though many electromyographers prefer not to perform them in routine practice 2, 3
• Absent or delayed conduction on the affected side compared to the contralateral side confirms the diagnosis 5

Treatment Approach for Meralgia Paresthetica

Conservative Management (First-Line)

• Remove the underlying cause: lose weight, avoid tight belts and trousers, correct leg length discrepancies 2, 3, 5
• Prescribe antineuropathic medication (gabapentin or pregabalin) for symptom control 3
• NSAIDs provide symptomatic relief 6
• Bed rest for 15 days and avoidance of the causative factor for 45 days can result in complete symptom resolution 6

Interventional Treatment (If Conservative Fails)

• Ultrasound-guided diagnostic nerve block with local anesthetic (10 mL bupivacaine 0.25%) provides immediate pain relief and confirms the diagnosis 2, 6
• Local injection with anesthetics and corticosteroids has limited evidence but can be attempted 3
• Pulsed radiofrequency treatment of the LFCN should only be performed in a research context due to limited evidence 3
• Surgical decompression of the LFCN is reserved for cases where conservative and interventional treatments fail 4

Critical Clinical Pitfalls

• Do not assume this is lumbar radiculopathy without confirming the pain distribution stays above the knee 1, 6
• Anatomical variants of the LFCN occur in 25% of patients and may cause negative response to diagnostic blocks 3
• Entrapment can occur at the fascia lata level rather than the inguinal ligament in rare cases 4
• Do not proceed to advanced imaging without first attempting conservative management for suspected meralgia paresthetica 2, 3
• Always screen for red flags including tumors, lumbar disc herniations, stress fractures, and infections before settling on a benign diagnosis 8, 1, 3