So let's start with a case.
A 6-year-old boy who
presents with weakness.
This 6-year-old boy
presents for new evaluation
of weakness and
The boy was born at 37 weeks by
uncomplicated vaginal delivery.
He met all milestones well until
about 3 years ago or 3 years of age,
when he first started having
difficulties with walking,
particularly running longer distances,
where he would get tired and weak.
Over the past several years,
he has had progressive weakness
with difficulty running,
jumping and climbing.
He has no other
He's an only child and his
mother is 42 years old,
and has had an abnormal
gait with arched back
but no other signs of weakness.
And she does see a cardiologist for an
unspecified heart rhythm abnormality.
Over the last 6 months, the boy's
weakness has continued to worsen.
He now has difficulty standing
up from a lying position.
His calf muscles are
enlarged and hypertrophied
bilaterally and symmetrically.
He has no problems breathing.
A neurologic examination shows
proximal weakness in the arms and legs.
Cranial nerves, sensory examination, reflex
exam and cerebellar exam are all normal.
Workup shows a markedly increased
creatine kinase over 40,000 IU/mL.
So what's the most
Well, let's go back and look through
some of the key details of this case.
First, we see that
this is a young child,
which is tipping us off that this
may be an inherited muscle disorder.
And the patient presents with progressive
weakness, which is really important
when we differentiate
the muscular dystrophies
from other inherited
causes of muscle disorders.
On the second part of the case,
we see a number of key findings.
First is the distribution.
This is proximal weakness, proximal
in the legs and proximal in the arms.
And that really puts us
into the bucket the category
of proximal predominant
What are the sensory findings?
Well, here we see the
sensory exam is normal.
The reflex exam is also normal.
And then there's a
fourth important wildcard
and that is calf
or hypertrophy or
which will point us in the
direction of a muscular dystrophy,
that and we see this really
elevated creatine kinase,
which points us to some type of
inflammation in and around the muscle.
So what's the most
Duchenne's muscular dystrophy,
dystrophy or Dermatomyositis?
Well, polymyositis is an
acquired cause of muscle disorder
and this patient presents with an age,
a sex and a distribution of weakness
that is not consistent,
inconsistent with polymyositis.
with a rash in addition to
which is inconsistent
with this case.
dystrophy can be seen
as a cause of muscular dystrophy
but this patient's age and sex
really points us to
Duchenne's muscular dystrophy.