Meralgia Paresthetica Causes, Symptoms, Diagnosis, Treatment

Meralgia Paresthetica Causes, Symptoms, Diagnosis, Treatment

Meralgia Paresthetica Causes, Symptoms, Diagnosis, Treatment

Meralgia paresthetica [also known as, lateral femoral cutaneous nerve entrapment], is the clinical syndrome of pain and/or neuropathy in the anterolateral thigh associated with compression of the lateral femoral cutaneous nerve [LFCN].

The lateral femoral cutaneous nerve branches off of the lumbar plexus and conveys fibers from the L2 and L3 nerve roots. The nerve courses through the pelvis, running adjacent to the lateral edge of the psoas muscle. It enters the leg underneath or through the inguinal ligament, medial to the anterior superior iliac spine; it is in this location that entrapment can occur. 

The lateral femoral cutaneous nerve is a pure sensory nerve that is susceptible to compression as it courses from the lumbar plexus, through the abdominal cavity, under the inguinal ligament, and into the subcutaneous tissue of the thigh.

Meralgia Paresthetica Causes, Symptoms, Diagnosis, Treatment

RISK FACTORS

Most cases of meralgia paresthetica arise spontaneously and are presumed to result from entrapment of the lateral femoral cutaneous nerve as it passes underneath or through the inguinal ligament.

The most commonly identified risk factors are:

• Obesity
• Diabetes mellitus
• Older age

The median age at when patients present with meralgia paresthetica is 50 years. 

The incidence is approximately 7 times higher in patients with diabetes compared with the general population.

Meralgia Paresthetica Causes, Symptoms, Diagnosis, Treatment

CAUSES AND RISK FACTORS

Examples related to compression at the inguinal ligament include:

• Body habitus (eg, large abdomen with overlying panniculus)
• Pregnancy
• Increased intraabdominal pressure due to ascites
• Tight belts or waistbands
• Compression from a wallet
• Prolonged leaning of a thigh against a bench or table
• Carrying heavy objects supported by the thigh or groin
• Long-distance walking, cycling, or circuit training, possibly related to local ischemia during repetitive muscle stretching
• Groin trauma, such as a seat belt injury in a motor vehicle crash

Meralgia Paresthetica Causes, Symptoms, Diagnosis, Treatment

SIGNS and SYMPTOMS

Meralgia paresthetica is characterized by pain, numbness and tingling (paresthesia), and diminished sensation (hypesthesia) over the upper outer thigh.

Symptoms are usually unilateral and typically the onset of pain is subacute. Patients characterize their symptoms as:

• Tingling or “pins and needles” sensation in the outer (lateral) part of the thigh
• Numbness in the outer (lateral) part of the thigh
• Burning in the outer (lateral) part of the thigh
• Itching in the outer (lateral) part of the thigh
• Hyperpathia, in which light touch (from clothing or a hand) results in unpleasant sensations in the outer (lateral) part of the thigh
• Pain sometimes tends to be unchanged with positional changes or activities including walking or standing has been reported in some studies. or,
• Pain in some cases can be aggravated by prolonged standing, walking, thigh extension and relieved by sitting
• Valsalva maneuvers or other activities such as cough, that increases intra-abdominal pressure may also aggravate the discomfort in some cases

Clinical examination shows a loss of light touch and/or pinprick sensation in a discrete area of the upper lateral thigh, often in a more restricted area than the zone of paresthesias.

Symptoms may be reproduced by tapping over the lateral aspect of the inguinal ligament (Tinel’s sign).

Neurologic findings are limited to sensory changes only, since the lateral femoral cutaneous nerve does not contain motor fibers. Therefore, if physical examination reveals motor deficits (e.g. weakness or abnormal deep tendon reflexes in the affected extremity), then other etiologies should be considered.

Meralgia Paresthetica Causes, Symptoms, Diagnosis, Treatment

EVALUATION

Detailed history must be obtained, especially about recent weight gain, use of tight-fitting clothes or belts, exercise habits, and other potential risk factors for compression at the inguinal ligament. [See ‘Causes and risk factors’ above].

Inquiring history about aggravating factors especially with with Valsalva or prolonged walking is helpful in suggesting inguinal compression.

If pain is present, it should be limited to the anterolateral part of the thigh. Back pain, including radicular pain or “sciatica,” should raise suspicion for lumbosacral spine or plexus pathology rather than meralgia paresthetica.

Neurologic examination:
A focused neurologic examination of the lower extremities must be performed in order to detect diminished sensation in the distribution of the LFCN and also to rule out weakness or reflex changes suggesting an alternative diagnosis.

• Sensory examination: Pinprick and light touch should be tested in the affected thigh.
  • Hypesthesia is typically covers approximately 10 inch by 5 inch oval shaped area on the anterolateral thigh.
  • Sensory abnormalities may also seen on the anterior thigh since the distribution of the LFCN is not strictly lateral .
  • The sensory examination is otherwise normal.
  • NOTE: although patients with diabetes may have sensory loss in a distal symmetric distribution, suggestive of a distal symmetric polyneuropathy.
• Motor examination: The motor examination should include bilateral muscle strength testing of all major muscle groups of the lower extremities and straight leg raise.
  • The straight leg raise should be negative.
  • Proximal and distal motor strength should be preserved.
• Deep tendon reflexes (DTRs)
  • DTRs should be symmetric in both legs.
  • Loss of the patellar or Achilles reflex on the side of the sensory abnormality suggests an alternative diagnosis, for example femoral neuropathy or L3/L4 radiculopathy [See below for ‘differential diagnosis’]

Meralgia Paresthetica Causes, Symptoms, Diagnosis, Treatment

DIAGNOSIS

-Clinical Diagnosis
Meralgia paresthetica is a clinical diagnosis based primarily upon all of the following features:

• Pain, paresthesia, and numbness in the lateral or anterolateral thigh.
• Sensory abnormalities (e.g., decreased pinprick) in the distribution of the lateral femoral cutaneous nerve.
• Absence of other neurologic abnormalities of the leg (e.g., muscle weakness and loss of reflexes)

 

-Imaging
Imaging is generally not necessary if the history and examination findings are characteristic for meralgia paresthetica. Patients with atypical signs or symptoms or an unreliable examination should be imaged to rule out alternative diagnoses.

• MRI of lumbosacral spine is the best study to assess for structural lumbosacral spine disease if there is clinical suspicion for an L3/L4 radiculopathy.
• Pelvic CT or MRI is appropriate if a lumbar plexopathy is being considered in order to look for tumor or hemorrhage.

 

-Nerve conduction studies (NCS)/electromyography (EMG)
Most patients with typical signs and symptoms of meralgia paresthetica do not require NCS/EMG.

Electrodiagnostic studies can assist in the differential diagnosis and guide the need for imaging of the lumbar spine or pelvis. The role of NCS/EMG is primarily to exclude an L3/L4 radiculopathy, lumbar plexopathy, or femoral neuropathy in patients with atypical clinical presentations.

• Absent or reduced sensory responses in the LFCN and delayed conduction across the inguinal ligament are supportive of meralgia paresthetica.
• The needle electromyography (EMG) study is normal in meralgia paresthetica, but abnormal in characteristic patterns in radiculopathies, plexopathies, and femoral neuropathies.

 

-Nerve Blockade
Pain relief achieved from anesthetic injection into your thigh where the lateral femoral cutaneous nerve enters into it can confirm that you have meralgia paresthetica. Ultrasound imaging might be used to guide the needle.

Meralgia Paresthetica Causes, Symptoms, Diagnosis, Treatment

DIFFERENTIAL DIAGNOSIS

The differential diagnosis of meralgia paresthetica consists of other peripheral nervous system lesions that supply overlapping sensory territory in the anterior and lateral thigh.

• L3/L4 radiculopathy – The L3 and L4 dermatomes primarily correspond to anterolateral thigh.
  • Muscular innervation of the anterior thigh is overlapping, and involvement of either level may produce weakness of hip flexion, knee extension, and hip adduction.
  • Radiculopathies secondary to nerve root compression typically involve back pain with radiation into the thigh and occasionally below the knee down the medial aspect of the leg.
  • Pain may be reproduced on straight leg raise testing and exacerbated by back movement, coughing, sneezing, or straining.
  • The most common causes of L3/L4 radiculopathy are nerve root compression due to disc herniation and spondylosis.

• Lumbosacral plexopathy – The lumbar plexus is derived from the anterior rami of the L1 through L4 nerve roots and runs along the psoas major muscle in the pelvis.
  • Lumbar plexus lesions tend to cause weakness of hip flexion and adduction and/or knee extension. Sensory disturbances usually involve the anterior and medial thigh.
  • The most common causes are diabetic amyotrophy, idiopathic lumbosacral radiculoplexus neuropathy, retroperitoneal or pelvic tumors, and retroperitoneal hematomas.

• Femoral neuropathy – The femoral nerve is the largest nerve emerging from the lumbar plexus. It passes under the inguinal ligament medial to the lateral femoral cutaneous nerve of the thigh. The femoral nerve innervates the anteromedial skin of the thigh (via the medial femoral cutaneous branch) as well as medial lower leg via the saphenous nerve.
  • Weakness typically involves the quadriceps muscle group (knee flexion) with sparing of adduction and variable involvement of hip flexion.
  • The knee jerk reflex is usually lost.
  • Common causes include iatrogenic surgical injury, hip or pelvic fractures, and masses or hematomas within the iliacus muscle.

 

Meralgia Paresthetica Causes, Symptoms, Diagnosis, Treatment

TREATMENT

-Initial therapy

Meralgia paresthetica is a self-limited, benign disease in most patients and most patients have spontaneous remission.

Although recurrent symptoms are common approximately more than 90% of patients respond to conservative measures alone.

The acute therapy of meralgia paresthetica includes:

• Educating and reassuring. This is a benign condition and it will resolve spontaneously.
• Reducing pressure over the nerve in the groin area by avoiding tight clothing and belts.
• Weight loss if appropriate.
• Use of oral nonopioid analgesics such as acetaminophen, NSAIDs, and salicylates, may be effective for some patients.

Physical therapy does not play a significant role in the management of this disorder. 

-Persistent symptoms

In patients with persistent symptoms for more than 1 to 2 months, despite the above measures, reexamining the area to confirm the local nature of the problem is important.

Anticonvulsants such as carbamazepine, phenytoin, or gabapentin may be helpful in reducing neuropathic pain symptoms but have not been systematically studied in meralgia paresthetica.

Tricyclic antidepressants such as amitriptyline may aid in relieving pain.

Consultation with an anesthesiologist for a local nerve block can also be considered for persistent symptoms. Injection of a local anesthetic agent, glucocorticoid, or both can be useful to temporarily treat this neuropathy.

Rarely, surgery is necessary in patients with severe chronic symptoms that are refractory to more conservative measures.

• Surgical release: decompression of the nerve may provide long-lasting relief in some patients.
  • This procedure has the advantage of preserving sensory function. However, it is not uniformly successful.

• Nerve transection: sectioning of the lateral femoral cutaneous nerve as it exits the pelvis is the most definitive procedure, but has the disadvantage of permanent anesthesia.
  • From a practical point of view, only patients with intractable dysesthetic pain are willing to undergo a procedure that results in permanent anesthesia.

 

 
Meralgia Paresthetica Causes, Symptoms, Diagnosis, Treatment
Source: [1],[2],[3],[4]