RT Book, Section
A1 Martin, John H.
SR Print(0)
ID 1129849833
T1 The Cerebellum
T2 Neuroanatomy Text and Atlas, 4e
YR 2016
FD 2016
PB McGraw-Hill Medical
PP New York, NY
SN 9780071603966
LK neurology.mhmedical.com/content.aspx?aid=1129849833
RD 2024/04/19
AB CLINICAL  CASE  |  Friedreich  AtaxiaA  10-year-old  boy  first  presented  to  his  pediatrician  with  difficulty  walking.  He  was  an  only  child,  of  French-Canadian  parents.  His  parents  reported  that  recently  he  has  difficulty  standing  still,  is  constantly  shifting  his  position,  and  difficulty  running.  They  reported  normal  motor  development  initially,  but  that  now  he  seems  clumsy.  On  examination,  he  was  observed  to  have  a  wide-based  gait  with  occasional  shifting  of  position  to  maintain  balance.  Sitting  and  standing  were  noted  to  be  associated  with  titubation.  He  was  referred  to  a  child  neurologist.  After  further  workup  and  genetic  testing,  he  was  diagnosed  with  Friedreich  ataxia,  a  progressive  spinocerebellar  ataxia.  Friedreich  ataxia  is  an  autosomal  recessive  disorder,  due  to  a  chromosome  9  mutation  that,  in  virtually  all  cases,  is  an  expansion  of  a  GAA  trinucleotide  repeat  within  the  gene  that  codes  for  the  mitochondrial  protein  frataxin.He  was  seen  regularly  by  his  neurologist  who  noted  progression  in  motor  signs  to  include  upper  extremity  ataxia,  dysdiadochokinesia,  and  intention  tremor.  When  asked  to  maintain  a  standing  posture  with  his  eyes  closed,  he  began  to  sway  and  loose  his  balance  (positive  Romberg  sign).  He  had  no  tendon  reflexes,  such  as  the  knee-jerk  or  biceps  reflexes.  Friedreich  ataxia  patients  often  have  cardiomyopathy,  and  most  patients  die  as  a  result  of  cardiac  arrhythmia  or  congestive  heart  failure.Figure  13–1A  is  an  MRI  from  a  young  Friedreich  ataxia  patient.  Compared  with  the  MRI  from  a  healthy  person  (Figure  13–1B),  the  most  notable  feature  is  narrowing  of  the  cervical  spinal  cord.Answer  the  following  questions  based  on  your  reading  of  the  case  and  the  chapter.1.  Why  does  the  patient  have  a  positive  Romberg  sign,  and  how  is  this  related  to  the  loss  of  tendon  reflexes?2.  What  could  account  for  the  wide-based  gait  and  ataxia?Key  neurological  signs  and  corresponding  damaged  brain  structuresProprioceptive  and  reflex  signsThe  cervical  spinal  cord  in  the  patient  is  thin  compared  with  a  healthy  person.  Thinning  is  produced  by  degeneration  of  large-diameter  somatic  sensory  afferents;  unmyelinated  fibers  are  spared.  The  degeneration  is  in  the  dorsal  columns.  Whereas  the  degeneration  is  accompanied  by  gliosis,  it  is  insufficient  to  maintain  the  normal  size  of  the  cord.  The  dorsal  roots  show  thinning  as  well.  With  this  large-diameter  fiber  loss,  there  is  associated  loss  of  tendon  reflexes  and  limb  proprioception.  Patients  with  this  sensory  loss  rely  on  vision  to  help  maintain  balance.  Often  patients  have  impairment  in  tactile  sensation.AtaxiaThe  loss  of  limb  proprioceptive  information  leads  to  incoordination.  Further,  there  is  loss  of  neurons  in  Clarke's  column,  which  transmit  proprioceptive  and  other  mechanosensory  information  to  the  cerebellum;  these  neurons  give  rise  to  the  dorsal  spinocerebellar  tract  (Figure  13–6B).  Together  these  factors  contribute  to  ataxia.  To  compensate  for  boththe  balance  impairment  and  impaired  lower  extremity  coordination,  patients  adopt  a  broad-based,  slowed  gait.  Interestingly,  Friedreich  ataxia  patients  may  not  show  extensive  cerebellar  degeneration  for  most  of  the  course  of  the  disease.  Thus,  the  ataxia  may  be  more  related  to  the  somatic  sensory  loss.  In  this  way,  it  is  similar  to  motor  disturbances  in  neurosyphilis  (see  Clinical  Case  in  Chapter  4).  Absence  of  early  ...