Sequential involvement of the nervous system in subacute combined degeneration.
OBJECTIVE
Subacute combined degeneration (SCD) involves progressive degeneration 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 component in the central nervous system and peripheral nervous system is different, it is improbable that these cells undergo simultaneous degeneration. However, the sequence of degeneration in SCD has not been established.


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.


CONCLUSIONS
In SCD, degeneration appears to progress in the following order: lower spinal cord, cervical spinal cord, peripheral nerve/optic nerve, and finally, the brain.
Department of Neurology, College of Medicine, Hallym University, Seoul, Korea.
Yang-Ki
YK
Minn
Seung-Min
SM
Kim
Se-Hoon
SH
Kim
Ki-Han
KH
Kwon
Il-Nam
IN
Sunwoo
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005073:Evoked Potentials, Somatosensory / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D052879:Subacute Combined Degeneration / Q000097:blood* / Q000378:metabolism / Q000503:physiopathology*; D014805:Vitamin B 12 / Q000097:blood; D014806:Vitamin B 12 Deficiency / Q000097:blood / Q000150:complications; D055815:Young Adult
D014805:Vitamin B 12