TY  - CHAP
M1  - Book, Section
TI  - Somatic Sensation: Spinal Mechanosensory Systems
A1  - Martin, John H.
PY  - 2021
T2  - Neuroanatomy: Text and Atlas, 5e
AB  - CLINICAL  CASE  |  Loss  of  Vibration  Sense  and  Limb  ProprioceptionA  36-year-old  man  was  admitted  to  the  hospital  for  unsteadiness  of  gait  and  several  other  somatic  sensory  and  motor  signs,  including  pain  and  limb  strength  impairments.  Sensation  to  touch,  pinprick,  and  temperature  were  normal.  Perception  of  vibration  and  limb  position  sense  were  absent.  When  he  was  asked  to  stand  upright  with  his  eyes  closed,  he  swayed  and  lost  balance.  His  gait  was  broad  based,  clumsy,  and  staggering.  MRI  of  his  brain  was  normal  but  MRI  of  his  spinal  cord  showed  an  intense  signal  in  the  dorsal  columns,  bilaterally  (Figure  4–1A),  that  appeared  to  be  the  same  as  CSF.  On  interview,  the  patient  told  the  resident  that  he  had  an  untreated  syphilitic  infection  for  10  or  more  years.Try  to  answer  the  following  questions  based  on  your  reading  of  the  chapter,  earlier  readings,  inspection  of  the  case  images,  and  consideration  of  the  neurological  signs.1.  What  are  the  cellular  constituents  and  processes  in  the  dorsal  column  of  a  healthy  individual?2.  What  is  the  origin  of  the  principal  neural  cells  and  cellular  processes  in  the  dorsal  column?3.  What  functional  system  becomes  impaired  when  there  is  neuronal  degeneration  in  the  dorsal  columns?4.  What  distinguishes  the  spinal  neural  substrates  of  vibration  sense  and  proprioception  from  pain,  temperature,  and  itch.  And  why  might  touch  sensation  have  been  preserved?5.  What  is  Romberg’s  sign  and  why  does  the  patient  demonstrate  this  sign?Conclusion:  The  patient  was  diagnosed  with  neurosyphilis,  also  called  tabes  dorsalis,  on  the  basis  of  neurological  tests  and  several  laboratory  tests,  including  the  MRI  and  the  sensory  modality  loss.  This  is  the  advanced  stage  of  syphilis,  when  it  infects  the  nervous  system.Key  neurological  signs  and  corresponding  damaged  brain  structuresNeurosyphilisSyphilis  is  normally  treated  with  penicillin.  Left  untreated,  the  infectious  agent—the  spirochete,  Treponema  pallidum—infects  the  nervous  system.  In  time,  this  can  result  in  dysfunction  or  degeneration  of  its  neuronal  targets.  Common  target  neurons  are  the  dorsal  root  ganglion  sensory  neurons,  which  are  important  for  mechanosensation.  Especially  vulnerable  is  limb  position  sense  (or  limb  proprioception),  which  is  signaled  by  muscle  and  joint  sensory  receptors,  and  vibration  sense,  which  is  signaled  by  Pacinian  corpuscles.  At  autopsy,  tabetic  patients  can  show  degeneration  of  the  dorsal  columns,  which  is  revealed  by  staining  histological  sections  of  the  spinal  cord  for  myelin.  Oligodendrocytes  also  degenerate  in  regions  where  axons  have  degenerated,  therefore  showing  demyelination  (Figure  4–1B).  The  region  of  intense  signal  on  the  MRI  demonstrates  damaged  dorsal  column  fibers.Loss  of  limb  proprioception  and  vibration  senseBoth  of  these  senses  are  mediated  by  dorsal  root  ganglion  neurons  that  have  a  large-diameter  axon,  which  project  rostrally  within  the  dorsal  columns.  In  the  absence  of  limb  proprioceptive  afferents,  patients  rely  on  vision  to  compensate  for  the  loss  of  sensory  awareness  of  their  limbs.  This  explains  Romberg’s  sign,  the  loss  of  balance  when  the  patient  closed  his  eyes.  Touch  is  preserved  in  this  patient;  there  may  be  diminished  sensitivity  or  discriminative  capacity  due  to  the  loss  of  the  large-diameter  mechanosensory  fibers,  but  this  was  not  tested.  Dorsal  root  ganglion  mechanosensory  neurons  with  a  small-diameter  ...
SN  - 
PB  - McGraw Hill
CY  - New York, NY
Y2  - 2024/04/19
UR  - neurology.mhmedical.com/content.aspx?aid=1189287224
ER  -