CROSS-SECTIONAL AREA REFERENCE VALUES OF NERVES IN THE LOWER EXTREMITIES USING ULTRASONOGRAPHY HUNG YOUL SEOK, MD, 1 JAE HONG JANG, MD, 1 SUN JAE WON, MD, 2 JOON SHIK YOON, MD, PhD, 3 KYUNG SEOK PARK, MD, PhD, 4 and BYUNG-JO KIM, MD, PhD 1 1 Department of Neurology, Korea University College of Medicine, Seoul, #73, Inchon-ro, Seongbuk-gu, Seoul, 136–705, South Korea 2 Department of Rehabilitation Medicine, Yeouido St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, South Korea 3 Department of Rehabilitation Medicine, Korea University College of Medicine, Seoul, South Korea 4 Department of Neurology, Seoul National University Bundang Hospital, Seoul National University, College of Medicine, Seoul, South Korea Accepted 10 February 2014 ABSTRACT: Introduction: Cross-sectional area (CSA) reference values of lower extremity nerves using ultrasonography have only been reported in a few studies and have been limited to white populations. Methods: For this study, 94 healthy Korean volunteers were recruited for measurement of the CSA at 7 sites of lower extremity nerves. The side-to-side difference in CSA was calculated for each nerve, and reference ranges were derived. External validity evaluation for the reference values was performed with 10 newly recruited volunteers at a different institution. Results: Nerve CSA was correlated significantly with body mass index, weight, and height; however, the absolute value of the side-to-side difference had no significant correlation with demographic factors. The external validity was adequate for all sites, ranging from 80% to 100%. Conclusions: The lower extremity nerve CSA values obtained in this study may provide normal reference values for the Asian population. Muscle Nerve 50: 564–570, 2014 High-resolution ultrasonography permits direct assessment of extrinsic and intrinsic abnormalities of peripheral nerves, thus compensating for the limitations of electrodiagnostic studies. 1–7 Although various ultrasonographic variables have been sug- gested for assessment of abnormalities of periph- eral nerves, 8–21 the most widely accepted variable is the cross-sectional area (CSA), determined by posi- tioning the probe perpendicular to the nerve. Determination of normal reference values for nerve CSA is essential to identify abnormal nerves. CSA reference values of upper extremity nerves have been described in a relatively large number of reports from white populations, 8,13,22–25 and several recent studies have also been conducted in Asian populations 18,26–28 ; there is limited information on normal reference values for lower extremity nerve CSA, and such studies are limited to white popula- tions. 8,13,29–32 Although previous studies have shown an association between nerve CSA and demographic factors such as gender, age, height, weight, and body mass index (BMI), 8,13,17,18,22–25,28,32 the refer- ence values for white populations may not be appli- cable directly to Asian populations due to significant differences in body habitus between the 2 ethnic groups. The aims of this study were to establish normal reference values for nerve CSA of lower extremity nerves in a healthy Korean population and to assess the external validity of our reference values. METHODS Participants and Evaluation. We recruited healthy volunteers between ages 20 and 69 years. Partici- pants were selected to yield an equal number of men and women (approximately 10 men and 10 women in each age decade). Subjects were excluded from the study if they had a history of relevant peripheral nerve disease. Physical exami- nation and F-wave studies in the right median and posterior tibial nerves were performed as screening tests, and subjects who showed any neurological abnormality or a delay in F-wave latency were excluded. Age, gender, height, and weight were recorded prior to ultrasound examination. BMI was calculated as weight in kilograms divided by height in square meters (kg/m 2 ). Written informed consent for study participa- tion was obtained from all subjects. This study was approved by our institutional review board. Ultrasonography. Ultrasonography was performed with a Philips HD15 system (Philips Ultrasound, Bothell, Washington) and a 5–12-MHZ linear-array transducer. All measurements were collected by an expert ultrasonographer who had at least 3 years of experience in musculoskeletal ultrasonography. All subjects were scanned bilaterally. Nerve CSA was measured at the following loca- tions: sciatic nerve, mid-thigh and popliteal fossa; common fibular nerve, popliteal crease and fibular head; posterior tibial nerve, popliteal crease and 7 cm proximal to the medial malleolus; and sural nerve, distal calf. These locations were chosen based on several factors, including anatomical landmarks and clinically important points. Each Abbreviations: BMI, body mass index; CSA, cross-sectional area Key words: cross-sectional area; lower extremity; nerve ultrasound; normal; reference values K.S.P. and B.-J.K. contributed equally to this study. Correspondence to: B.-J. Kim; e-mail: nukbj@korea.ac.kr and K.S. Park; e-mail; pks1126@chol.com V C 2014 Wiley Periodicals, Inc. Published online 12 February 2014 in Wiley Online Library (wileyonlinelibrary. com). DOI 10.1002/mus.24209 564 Normal CSA of Lower Limb Nerves MUSCLE & NERVE October 2014