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Adding an Ultrasound Scan Before the Injection Reveals a Rare Cause of Meralgia Paresthetica: Inguinal Lymphadenomegaly

Palamar, Deniz MD; Misirlioglu, Tugce Ozekli MD; Arslan, Hakan MD; Akgun, Kenan MD

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American Journal of Physical Medicine & Rehabilitation: August 2020 - Volume 99 - Issue 8 - p e93
doi: 10.1097/PHM.0000000000001279
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A 39-yr-old man presented with a 1-yr history of numbness on the anterolateral region of his left thigh. He had previously visited an orthopedic surgeon and was referred to electrophysiology department with prediagnosis of meralgia paresthetica (MP). Electrophysiological evaluation was consistent with MP, with no sensory conduction in the left lateral femoral cutaneous nerve (LFCN). The patient was then referred to our physiatry outpatient clinic for further evaluation and interventional treatment because there was no response to conservative pharmacotherapy with nonsteroidal anti-inflammatory drugs and neuropathic pain agents for 6 months.

He denied any history of trauma, weight gain, or wearing tight clothes. His physical examination was normal, except for loss of sensation along the LFCN distribution and tenderness around the anterior superior iliac spine. Ultrasound (US)-guided injection of LFCN for diagnostic and therapeutic purposes was then planned.

During the tracking of the left LFCN, approximately 1 cm medial to anterior superior iliac spine, a well-defined, hypoechoic nodular lesion with a diameter of 14 × 2 mm, compatible with a lymph node, in close proximity with the LFCN was noted (Fig. 1, Video). There was no vascularity on color Doppler. Sonographic palpation was positive just above the lesion site. Considering MP secondary to inguinal lymph node enlargement, the injection procedure was quitted, and the patient was referred to a plastic surgeon for the excisional biopsy.

FIGURE 1
FIGURE 1:
Short axis view of the lateral femoral cutaneous nerve (arrowheads) in close proximity with the inguinal lymph node (between the cursors). ASIS, anterior superior iliac spine.

Before the surgery, US was reperformed so as to do the skin marking. An enlarged lymph node with a diameter of 1.5 × 0.5 × 0.2 cm, just under the skin mark was detected. The histopathological study of the resected mass confirmed the diagnosis of reactive lymph node hyperplasia. No further evaluation was needed because the patient had a dramatic symptomatic relief after the surgery.

Meralgia paresthetica, the entrapment of the LFCN, is usually idiopathic but can also be caused by a variety of conditions, such as obesity, pregnancy, wearing of tight clothes, surgery, or masses located nearby the nerve. Although the diagnosis is usually made clinically based on the typical symptoms of paresthesia, numbness and pain over the anterolateral aspects of the thigh; electrodiagnostic studies can also be used to verify the diagnosis. In recent years, US of the LFCN has also been proposed as a powerful diagnostic aid for MP. Besides confirming the entrapment morphologically, the US has an advantage of uncovering the underlying cause and guiding the injections.1

The treatment of MP should start with a conservative treatment protocol comprising regulation of activities of daily living, reduction of aggravating factors, and pharmacotherapy. If this regimen fails, local injection of the LFCN with local anesthetic with or without corticosteroid may then be performed.2

The LFCN injections can either be performed blindly using the anatomic landmarks or can be performed with imaging-guided techniques, such as US and fluoroscopy.

According to our knowledge, there is only one report in literature regarding femoral neuropathy caused by compression of the femoral nerve by the enlarged lymph nodes in the inguinal region.3 Besides presenting a very rare cause of MP, we want to emphasize the superiority of US of the LFCN before the injection in treatment of MP.

REFERENCES

1. Tagliafico A, Serafini G, Lacelli F, et al.: Ultrasound-guided treatment of meralgia paresthetica (lateral femoral cutaneous neuropathy): technical description and results of treatment in 20 consecutive patients. J Ultrasound Med 2011;30:1341–6
2. Harney D, Patijn J: Meralgia paresthetica: diagnosis and management strategies. Pain Med 2007;8:669–77
3. Khella L: Femoral nerve palsy: compression by lymph glands in the inguinal region. Arch Phys Med Rehabil 1979;60:325–6
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