Ultrasound in Anatomical Variation of Lateral Femoral Cutaneous Nerve.

We read with great interest the recently published brief commentary by Onat and colleagues entitled “Ultrasound-Guided Diagnosis and Treatment of Meralgia Paresthetica”(1). In this paper, the authors presented an ultrasound (US) assessment of the lateral femoral cutaneous nerve (LFCN), whose entrapment is known as meralgia paresthetica (MP). They correctly determined that diagnosis of MP is substantially clinical and based on specific referred symptoms. Moreover, as the authors wrote, a nerve conduction study of LFCN is not routinely conducted. This point is very crucial, because the diagnosis of peripheral nerve diseases is often supported by an electrodiagnostic examination. Indeed, a nerve conduction study of LFCN is not easily performed because of structural features and the location of the nerve. Furthermore, important anatomical variations of the LFCN can occur in some cases (2). From a neurophysiological point of view, these characteristics make the nerve nearly inaccessible. US has shown its usefulness in peripheral nerve disease assessment for diagnosis, prognosis, treatment, and rehabilitation decisions (3,4). For this reason, US evaluation of this nerve may be considered mandatory and can represent the real completion of the clinical examination. US provides morphological information and can allow understanding nerve anatomy and abnormalities in real time. As the authors clearly showed, this approach can be helpful to define a diagnosis and decide on management. US is decisive for intervention guiding, because this technique, as Onat and colleagues described, can avoid the possible mistakes that occur during blind injection, simply based on anatomic markers (1). In fact, failures can happen in 60% of cases. This eventuality may be linked to nerve anatomic variability. The authors described the imaging technique of LFCN evaluation, positioning the probe at the level of the inguinal ligament and moving it finely. The nerve is visible and can be localized passing over, under, or through the ligament, usually close to the anterior superior iliac spine (ASIS). This US approach is absolutely correct, but on the basis of our experience, we would like to suggest a complementary method, based on the anatomic relationship between the LCFN and the sartorius muscle (SM). This muscle originates from the ASIS and runs towards the medial portion of the thigh. The probe can be positioned distal to the ASIS; in this way the LCFN is visible, superficially just over the SM, and can be proximally followed along its course (5). This anatomical relationship seems to be very comPain Physician 2016; 19:E1097-E1107 • ISSN 2150-1149