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.