Common anatomical variation in patients with idiopathic meralgia paresthetica: a high resolution ultrasound case-control study.

BACKGROUND Meralgia paresthetica (MP) is a mononeuropathy of the lateral femoral cutaneous nerve (LFCN) characterized by pain, numbness or paresthesia on the anterolateral aspect of the thigh. Though several contributing factors have been identified, the cause of its idiopathic form still remains unclear. Anatomic and clinical studies have demonstrated a variable course for the LFCN and have suggested a contribution to the pathogenesis of MP. OBJECTIVE It was the aim of the present case-control study to assess the anatomical course and compression site of the LFCN using high resolution ultrasound (HRUS) in patients suffering from idiopathic MP, and compare the anatomical course in these patients to an asymptomatic control group. STUDY DESIGN Case-control study. SETTING Nerve imaging center at a large university hospital in Austria. METHODS Twenty-eight patients with a diagnosis of MP were included in this study (20 men, 8 women; mean age 54 years). The diagnosis was established by clinical history, physical examination, and diagnostic anesthetic block. Fifteen age- and gender-matched healthy volunteers served as the control group. Standardized HRUS examinations were performed by one experienced radiologist from June 2004 through April 2012. Two experienced radiologists reviewed the patients' standardized HRUS examinations and performed examinations in the control group to measure the minimal distance between the LFCN and the anterior superior iliac spine (ASIS). OUTCOMES The minimal distance between the ASIS and the LFCN was measured using HRUS. RESULTS The LFCN could be seen in all patients and volunteers. In MP patients, the mean distance between the LFCN and the ASIS was 0.52 cm (SD 0.46 cm), compared to a mean distance of 1.79 cm (SD 1.48 cm) in the control group (P < 0.001). LIMITATIONS Limited sample size, retrospective design. CONCLUSIONS The results of this study demonstrate a significantly different course of the LFCN, closer to the ASIS in patients with idiopathic MP.