00:00
First, we need to talk about some important terminology. What's a myopathy and what's a
myositis? Well, a myopathy is any disease of the muscle. And this condition results from
dysfunction of the muscle, a problem with contraction or atrophy loss of muscle. And some
examples include skeletal muscle disorders. Most of our myopathies involve skeletal muscles.
00:24
This is different from a myositis. Myositis is inflammatory muscle disorder. So, it's an
inflammatory myopathy, a disorder of the muscle that results from inflammation. This often
occurs because of an autoimmune disease, either a circulating autoimmune disease that affects
the muscle, or a primary muscle autoimmune condition. And some examples that we'll review
are polymyositis and dermatomyositis. So, again, whenever we see a patient who is presenting
with a possible muscle condition, who is presenting with a chief complaint for weakness we
need to think of 3 things. What's the distribution? What are the sensory findings? And what's
the reflex exam? For most muscle conditions, we see a pattern that is proximal more than
distal and this is going to be true for our typical inflammatory myopathies or myositises, for
some of our inherited disorders, Duchenne muscular dystrophy and limb-girdle muscular
dystrophy. There are some important exemptions to that rule. And selected muscle disorders
have a more distal than proximal pattern and this includes inclusion body myositis and several
other muscle conditions. The sensory exam should be normal. The reflexes are often normal to
decreased. And importantly, we don't see bulbar findings. Many of our assessments include
the nerve conduction study or an EMG, electromyography, and we often see myopathic
findings, decreased motor units with normal or early recruitment. And we're going to talk a
little bit more about the nerve conduction velocity study and electromyography in our lecture
on peripheral neuropathies.