Original Article http://dx.doi.org/10.3349/ymj.2012.53.2.276 pISSN: 0513-5796, eISSN: 1976-2437 Yonsei Med J 53(2):276-278, 2012 Sequential Involvement of the Nervous System in Subacute Combined Degeneration Yang-Ki Minn,1 Seung-Min Kim,2 Se-Hoon Kim,3 Ki-Han Kwon, 1 and Il-Nam Sunwoo2 1Department of Neurology, College of Medicine, Hallym University, Seoul; Departments of 2Neurology and 3Pathology, Yonsei Medical Center, Yonsei University College of Medicine, Seoul, Korea. Received: March 21, 2011 Revised: April 26, 2011 Accepted: April 27, 2011 Corresponding author: Dr. Il-Nam Sunwoo, Department of Neurology, Yonsei University College of Medicine, 50 Yonsei-ro, Seodaemun-gu, Seoul 120-752, Korea. Tel: 82-2-2228-1600, Fax: 82-2-393-0705 E-mail: sunwooin@yuhs.ac ∙ The authors have no financial conflicts of interest. © Copyright: Yonsei University College of Medicine 2012 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non- Commercial License (http://creativecommons.org/ licenses/by-nc/3.0) which permits unrestricted non- commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Purpose: Subacute combined degeneration (SCD) involves progressive degenera- tion of the spinal cord, optic nerve, and peripheral nerves. Vitamin B12 (VB12) is a co-factor in myelin synthesis. Because each cell that constitutes the myelin compo- nent in the central nervous system and peripheral nervous system is different, it is improbable that these cells undergo simultaneous degeneration. However, the se- quence of degeneration in SCD has not been established. Materials and Methods: In this study, we analysed medical records and electrophysiological data of patients who showed neurological symptoms and whose serum VB12 levels were lower than 200 pg/mL. Results: We enrolled 49 patients in this study. Their mean VB12 level was 68.3 pg/mL. Somatosensory evoked potential (SEP) study showed abnormal findings in 38 patients. Of the 40 patients who underwent visual evoked potential (VEP) study, 14 showed abnormal responses. Eighteen patients showed abnormal findings on a nerve conduction study (NCS). In this study, abnormal posterior tibial nerve SEPs only were seen in 16 patients, median nerve SEPs only were seen in 3 patients, abnormal VEPs only in two, and abnormal NCS responses in one patient. No patient complained of cognitive symptoms. Conclusion: In SCD, degeneration appears to progress in the following order: lower spinal cord, cervical spinal cord, peripheral nerve/optic nerve, and finally, the brain. Key Words: Vitamin B12, subacute combined degeneration, spinal cord, somato- sensory evoked potential, nisual evoked potential INTRODUCTION Vitamin B12 (VB12) deficiency is thought to be an important cause of treatable neu- rological diseases. Clinically, it affects the spinal cord, peripheral nerves, optic nerve, and brain.1,2 VB12 is a co-factor in myelin synthesis.3,4 Because of the heterogeneity of myelinating cells in the central nervous system (astrocyte and oligodendrocyte) and peripheral nervous system (Schwann cell), it is improbable that myelinating cells in the above tracts degenerate simultaneously. However, the sequence of degenera- tion in subacute combined degeneration (SCD) has not been established. Nutritional neuropathies, including those due to VB12 deficiency, are uncom- mon in developed countries. However, in this era of intensive diabetes management, 276 Yonsei Med J http://www.eymj.org Volume 53 Number 2 March 2012