RT Book, Section
A1 Kasper, Dennis L.
A1 Fauci, Anthony S.
A1 Hauser, Stephen L.
A1 Longo, Dan L.
A1 Jameson, J. Larry
A1 Loscalzo, Joseph
SR Print(0)
ID 1128788463
T1 Muscle Diseases
T2 Harrison's Manual of Medicine, 19e
YR 2016
FD 2016
PB McGraw-Hill Education
PP New York, NY
SN 9780071828529
LK accessmedicine.mhmedical.com/content.aspx?aid=1128788463
RD 2024/04/19
AB APPROACH  TO  THE  PATIENT:  Muscle  DiseaseMuscle  diseases  (myopathies)  may  be  intermittent  or  persistent  and  usually  present  with  proximal,  symmetric  weakness  with  preserved  reflexes  and  sensation.  An  associated  sensory  loss  suggests  injury  to  peripheral  nerve  or  the  central  nervous  system  rather  than  myopathy;  on  occasion,  disorders  affecting  the  anterior  horn  cells,  the  neuromuscular  junction,  or  peripheral  nerves  can  mimic  myopathy.  Any  disorder  causing  muscle  weakness  may  be  accompanied  by  fatigue,  referring  to  an  inability  to  maintain  or  sustain  a  force;  this  must  be  distinguished  from  asthenia,  a  type  of  fatigue  caused  by  excess  tiredness  or  lack  of  energy.  Fatigue  without  abnormal  clinical  or  laboratory  findings  almost  never  indicates  a  true  myopathy.Muscle  disorders  are  usually  painless;  however,  myalgias,  or  muscle  pains,  may  occur.  Myalgias  must  be  distinguished  from  muscle  cramps,  i.e.,  painful,  involuntary  muscle  contractions,  usually  due  to  neurogenic  disorders.  A  muscle  contracture  due  to  an  inability  to  relax  after  an  active  muscle  contraction  is  associated  with  energy  failure  in  glycolytic  disorders.  Myotonia  is  a  condition  of  prolonged  muscle  contraction  followed  by  slow  muscle  relaxation.CK  is  the  preferred  muscle  enzyme  to  measure  in  the  evaluation  of  suspected  myopathies.  Electrodiagnostic  studies  (nerve  conduction  studies  and  electromyography,  NCS/EMG)  are  usually  necessary  to  distinguish  myopathies  from  neuropathies  and  neuromuscular  junction  disorders.  An  approach  to  muscle  weakness  is  presented  in  Figs.  195-1  and  195-2.