Diagnosis. — The  simultaneous  and  gradual  onset  of  weakness  and  wasting,
the  slow  but  progressive  increase  and  extension  of  the  symptoms,  render
the  diagnosis  of  the  developed  malady  simple  and  easy.  At  the  onset,  when
only  a  single  muscle  or  group  of  muscles  is  affected,  the  question  arises
whether  the  atrophy  is  local  or  is  the  commencement  of  a  wider  affection.
If  there  is  no  indication  of  a  peripheral  nerve  lesion,  local  atrophy  only
occurs  from  great  overuse  of  a  muscle,  commonly  one  of  the  small  muscles
of  the  hand,  from  some  manual  occupation,  and  in  a  person  of  feeble  general
strength.  If  such  cause  cannot  be  traced,  the  wasting  must  be  looked  on
with  grave  suspicion,  and  a  careful  and  repeated  examination  will,  in  most
cases,  soon  show  some  extension  of  the  atrophy.
In  multiple  neuritis,  the  onset  of  the  symptoms  is  subacute,  wasting  follows
weakness,  and  the  danger  of  confusion  is  with  subacute  myelitis  of  the  cornua,
not  with  their  slow  degeneration.  In  pachymeningitis  of  the  cervical  region,
with  considerable  damage  to  the  nerve  roots,  the  wasting  in  the  arms  may
resemble  that  of  progressive  muscular  atrophy,  and  there  are  often  weakness
and  rigidity  of  the  legs,  but  the  wasting  is  less  chronic  in  onset,  and  is  always
accompanied  by  distinctive  sensory  symptoms, — by  more  acute  pains,  and
by  anaesthesia,  irregular  in  distribution.  The  same  distinctions  suffice  for
the  diagnosis  in  diseases  of  the  nerve  roots  of  the  cauda  equina,  as  by  a
tumor.  This  may  cause  slow  wasting  in  the  legs,  but  there  is  always  severe
pain  and  loss  of  sensibility.
