Features that distinguish myopathy from neuropathy

By Alex Yartsev - Jul 01, 2015

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.

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