This has come up in Question 14.1 from the first paper of 2013, as well as Question 3.1 from the first paper of 2010. but in general it is a good thing to know about.

Features suggestive of myopathy:

  • The sensory supply should be preserved
  • The reflexes should be preserved
  • Weakness should be proximal - that is where the bigger muscles are, and the weakness there will be more obvious.
  • There should be no fasciculations

Also...

  • There may be myocardial involvement (skeletal myopathies tend to be associated with cadiomyopathy)
  • The muscles involved may be painful and tender(as in myositis)
  • There may be muscle contractures, requiring splints

Features suggestive of neuropathy:

  • Sensory loss may be present
  • Fasciculations may be present
  • There may be cranial nerve involvement
  • There may be dysautonomia

The College Answer from 2010

CICM produced this table as the answer to their own question, "What are the distinguishing features on clinical examination between a neuropathy and a myopathy?"

Neuropathy

Myopathy

Site of weakness

Distal weakness

Usually proximal

Sensory

May have concomitant sensory symptoms and signs

Usually pure motor

Reflexes

Reflexes lost early

Reflexes preserved till late

Fasciculations

Fasciculations may be present

Not typical

Contractures

Contractures not a feature

Contractures present

Myocardial dysfunction

Not a typical feature

May have accompanying cardiac dysfunction with the dystrophies

Additonal points can be made, if we move broadly, and somewhat away from clinical examination:

Neuropathy

Myopathy

Atrophy

Present

Absent until late

CK level

Normal

Elevated

Nerve conduction

Slowed

Normal

EMG

Fibrillations and fasciculations

Small motor units

MRI

Suble, near normal appearance

Enhancement of affected muscle

Muscle biopsy

Normal looking musckle

Irregular necrotic fibers

Yes, I suppose muscle biopsy is cheating.

References

Chapter   57   (pp. 617)  Neuromuscular  diseases  in  intensive  care by George  Skowronski  and  Manoj  K  Saxena

UpToDate: An approach to the patient with muscle weakness

Young, G. Bryan, and Robert R. Hammond. "A stronger approach to weakness in the intensive care unit." Critical care 8.6 (2004): 416.

Trojaborg, Werner, Louis H. Weimer, and Arthur P. Hays. "Electrophysiologic studies in critical illness associated weakness: myopathy or neuropathy–a reappraisal." Clinical neurophysiology 112.9 (2001): 1586-1593.

Šuput, Dušan, et al. "Discrimination between neuropathy and myopathy by use of magnetic resonance imaging." Acta neurologica scandinavica 87.2 (1993): 118-123.