Meralgia Paraesthetica

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Meralgia Paraesthetica

Meralgia paraesthetica is a neurological condition characterized by paraesthesia, hypaesthesia and/or dysaesthesia, primarily affecting the anterolateral aspect of the thigh. It results from compression or entrapment of the lateral femoral cutaneous nerve, a nerve that is primarily sensory, leading to altered sensation within its distribution.

The lateral femoral cutaneous nerve originates from the posterior branches of the L2 and L3 lumbar nerves and typically travels along the lateral border of the psoas muscle. Upon exiting the pelvis, the nerve usually passes beneath or through the inguinal ligament, medial to the anterior superior iliac spine (ASIS), although variations in its trajectory have been documented.

Distal to the inguinal ligament, the nerve divides into two branches:

• The anterior division provides sensory innervation to the anterior thigh, extending down to the knee.
• The posterior division innervates the lateral thigh, extending to the greater trochanter region.

The sensory changes characteristic of meralgia paraesthetica are confined to the areas innervated by the lateral femoral cutaneous nerve and typically do not extend below the knee. However, because similar symptoms can arise from lumbar radiculopathy, it is crucial to rule out this potential underlying cause during diagnosis.

Etiology 

The etiology of meralgia paraesthetica can be mechanical, metabolic, or postsurgical. In most cases, it occurs spontaneously, often due to entrapment of the lateral femoral cutaneous nerve as it passes beneath or through the inguinal ligament. The condition typically presents around the median age of 50 years. Systemic conditions, such as diabetes mellitus, can also adversely affect peripheral nerves, leading to generalized or localized neuropathies. The lateral femoral cutaneous nerve is particularly vulnerable to increased compressive forces. Notably, the incidence of meralgia paraesthetica is approximately seven times higher in individuals with diabetes compared to the general population.

The mechanical causes of lateral femoral cutaneous nerve compression, leading to meralgia paraesthetica, include:

• Body composition changes, such as a large abdomen with excess fat tissue (panniculus)
• Pregnancy
• Compression from external objects, including prolonged leaning against a bench or table
• Direct pressure from tight seat belts, belts, or restrictive clothing
• Groin trauma
• Surgical procedures, such as hip replacement or laparoscopic inguinal hernia repair

Since up to half of patients with meralgia paraesthetica can be identified as having a particular mechanical cause or triggering factor, they should be questioned about recent weight changes, the use of tight-fitting garments or belts, and changed exercise routines. Depending on the severity of the condition, management can be conservative, medical, or surgical.

Differential Diagnosis of Meralgia Paraesthetica

Several conditions should be considered in the differential diagnosis, including:

• Lumbar radiculopathy
• Lumbosacral plexopathy (damage or dysfunction affecting the lumbosacral plexus)
• Femoral nerve neuropathy
• Pelvic neoplasm
• Retroperitoneal haemorrhage
• Inguinal hernia

• Paraesthesia, dysaesthesias, or hypaesthesia in the anterolateral thigh, presenting as numbness, pins and needles, burning, crawling, or itching sensations.
• Symptoms are typically unilateral and develop gradually over days or weeks.
• Symptoms may worsen with activities involving prolonged or repetitive hip extension, such as walking or standing for extended periods.
• Hip flexion postures (e.g., sitting) often provide relief.
• Patients may report a link between symptom onset or exacerbation and tight-fitting clothing, belts, or other external pressure around the hip
• A history of recent weight gain, changes in exercise routine, localized injury, or surgical procedures in the region (e.g., hernia repair or hip. replacement) may be contributing factors.

• Decreased sensation to light touch and/or pinprick in the distribution of the lateral femoral cutaneous nerve, with some patients occasionally experiencing hypersensitivity to light touch
• Hair loss in the affected area may be observed in some cases, likely due to constant rubbing or irritation
• Positive Tinel Sign over the lateral femoral cutaneous nerve
  
• Positive Pelvic Compression test
• Positive Lateral Femoral Cutaneous Nerve Traction test

Meralgia paraesthetica is primarily a clinical diagnosis characterized by sensory loss or abnormal sensations in the upper thigh, while other neurological findings remain normal. In most cases, imaging or nerve conduction studies are not necessary. However, these diagnostic modalities may be considered if there is suspicion of underlying conditions such as osseous lesions, spinal disc pathology, or radiculopathy.

The following are examples of red flags for patients presenting with leg symptoms:

• A history of significant injury
• Severe pain
• Unrelenting pain
• Nocturnal pain
• Unexplained weight loss
• Fever
• Deformity
• Significant swelling
• Presence of upper extremity tingling, numbness, burning, or other neurological impairment
• Significant loss of range of motion
• Severe tenderness on palpation or severe pain with any examination procedure

If any red flags are identified during history taking and clinical examination, referral for urgent medical evaluation and further investigation is warranted.

Paraesthesia, Dysaesthesia or Hypaesthesia?

• Paraesthesia: Paraesthesia refers to abnormal sensations such as tingling, prickling, numbness, or “pins and needles.” Patients often describe these sensations as feeling like “creeping” or “crawling” on the skin. These sensations occur without obvious external stimulation and are commonly associated with nerve dysfunction or damage.
• Dysaesthesia: Dysaesthesia encompasses a broader range of unpleasant or uncomfortable sensations, including burning, itching, stabbing, or electric shock-like feelings. Unlike paraesthesia, dysaesthesia can be triggered by ordinary tactile or painful stimuli, resulting in a distorted perception. It often arises from nerve dysfunction but may involve more complex neurological processes.
• Hypaesthesia: Hypaesthesia refers to reduced sensitivity to touch or other sensory stimuli, often experienced as numbness or decreased sensation in a specific area. This condition can result from nerve damage, neurological disorders, circulatory issues, or the side effects of certain medications.

Differentiating Causes of Anterolateral Thigh Sensory Disturbance

• Meralgia Paraesthetica: Sensory disturbance without additional neurological findings.
• Pelvic Tumours or Haematomas: Sensory disturbance accompanied by motor impairment of muscles innervated by the femoral nerve or lumbosacral plexus.
• Lumbosacral Pathology: Sensory disturbance with motor impairment and low back pain.