00:00
What’s our clinical approach to muscle disorders? Well, there’s some things we expect to be
normal and there’s some findings that we expect to be abnormal that will point us in the
direction of this problem. Muscle conditions present typically with the chief complaint of
weakness, and we see problems with strength on exam. Typically, this is proximal, problems
with the proximal legs and proximal arms. Patients have difficulty walking upstairs, arising
out of chairs, reaching up to the top cabinet of a kitchen or elsewhere in their home. We
don’t see problems with mental status. Cranial nerve or bulbar findings are absent. And we
should see normal to slightly reduced reflexes and normal sensation. This is different from a
neuromuscular junction disorder. Where we do see weakness but the distribution is weakness
that also involves the bulbar findings and bulbar fibers. We see ptosis and diplopia, dysarthria,
dysphagia. We may not hear about those on history, but we should interrogate them on
exam. And for a patient presenting with proximal weakness, the most important first step in
our examination is to look for bulbar findings. For neuromuscular junction disorders, we also
see that mental status is normal. Reflexes are typically normal or slightly reduced which is
similar to problems arising from the muscle. And sensory findings are not present or are
minor for neuromuscular junction conditions. Both of these differ from the nerve and problems
arising from the nerve. With peripheral nerve disorders, we can see weakness. It often follows
a dermatomal pattern. We typically see reduced reflexes or even areflexia. And this is the
first level of the nervous system where we start to see areflexia in most conditions. And
importantly the vast majority of nerve problems are sensory motor neuropathies or nerve
disorders since we start to see sensory complaints and sensory findings on exam. Again, the
mental status and cranial nerve findings are often normal, though there are certain nerve
conditions that affect the peripheral nerve and the cranial nerve. So, let’s take a step back
and think more about the muscle. What types of muscles the patients have problems with,
with muscle disorders and where should we focus our examination and our findings? Well,
there are 3 types of muscles in the body. There is skeletal muscle, smooth muscle typically
around the blood vessels that’s where we think of the smooth muscle, and cardiac muscle.
02:21
Most myopathic conditions primarily affect the skeletal muscle. There are some inherited
disorders that will also affect the cardiac muscle. And it’s very uncommon for us to see
smooth muscle problems in patients with muscle disorders but it can be important in certain
inherited or genetic conditions. So, let’s look closer at the structure of the muscle. Recall
that a muscle body is composed of many different muscle fibers. That’s contained within the
epimysium, the fascia layer around the muscle. Muscle fibers are contained within an
endomysium, and then we get down to the individual muscle fibers. Recall that the cell
membrane around the muscle is called the sarcolemma.