A 3 year old boy presents to
the office with his mother.
She states that her son seems
weak and unwilling to walk.
He learned to walk recently and
had notable developmental delay.
The mother states that some of the boys on her
side of the family have had similar symptoms
and she worries that her son
might have the same condition.
A genetic study is performed that reveals an
absence of normal functioning dystrophin.
Which of the following is
the most likely diagnosis?
Answer choice (A) - Duchenne muscular dystrophy
Answer choice (B) -
Becker muscular dystrophy
Answer choice (C) - Limb-girdle muscular dystrophy
Answer choice (D) - myotonic muscular dystrophy
And answer choice (E) -
Emery-Dreifuss muscular dystrophy
Now take a moment to come to the answer
alone before we go through it together.
Now let's jump into this question together.
The first thing we need to do is determine
what kind of subject we're dealing with.
Now this is a condition of pathology and the organ
here seems to be the musculoskeletal system.
So this is muscoloskeletal pathology.
So this is a 2-step question.
We have to be able to understand what is the
underlying conditions described clinically
and then come to a diagnosis
as to what it's called.
And the stem is absolutely required to
understand the genetic study results
and also the clinical history
and exams of the patient.
Now let's walk through this question together.
The first thing we need to do is
understand what are the symptoms
that are actually suggestive of an
inherited muscular dystrophy.
Now muscular dystrophy is characterized by
progressive weakness and loss of muscle mass.
And the symptoms of most common types of
muscular dystrophy actually begin in childhood
and are most commonly seen in males.
And the majority of cases have
a positive family history.
But there are of course cases in
which no family history is present
and that is due to a
spontaneous gene mutation.
So it appears from this case that the patient does
have progressive weakness, loss of muscle mass.
He is a young male and he is
having this early in childhood
and he has a positive family history, thus
suggesting an inherited muscular dystrophy.
Now we need to determine what type of
muscular dystrophy this patient may have
Now this presentaton would suggest
Duchenne mucular dystrophy
which has an onset early in childhood
and commonly affects males.
Now Duchenne muscular dystrophy is caused
by an absence of functional dystrophin
and that's what we'll see here in the genetic
study - an abnormal functioning dystrophin.
Now let's refer to the image to help
us understand why it's important.
So this image shows the pathophysiology
of Duchenne's muscular dystrophy.
As we can see above, we have a muscle,
and then the muscle fiber.
There we have the extracellular
matrix, a membrane protein complex,
and dystrophin which connects the
actin to the actual cell membrane.
And it is dystrophin that actually converts the
actin and myosin filaments to the cell membrane.
And the absence of dystrophin will cause muscle
wasting and weakness in muscle function.
Thus in this case, the answer choice for this patient, or in this
case is Duchenne muscular dystrophy or answer choice (A).
Now let's look at some of the other answer choices.
Now, Becker msucular dystrophy, which
some people consider as 'milder' Duchenne
is unlikely as these symptoms
generally begin in the teenage years.
Now the other option, limb-girdle
muscle dystrophy is also unlikely
as hip and shoulder muscles are usually
affected first, not leg as in this case.
Myotonic muscular dystrophy is also unlikely as facial and
neck muscles are usually affected first - not the case here.
And Emery-Dreifuss muscular dystrophy is unlikely as this
presentation is generally seen in teenage years as well.
Let's review some high-yield facts regarding
muscular dystrophy and Duchenne muscular dystrophy.
Now the group of diseases that are characterized as progressive
weakness and loss of muscle is called muscular dystrophy.
And the condition is cause by gene mutation that interfere
with the production of key proteins for muscle health.
Now there are several different types of muscular dystrophy,
many of which are mentioned in the question answer choices.
But the most common form is Duchenne muscular dystrophy
which currently affects roughly 1 in 3500 males.
Some variants of muscular dystrophy present in childhood
while others present later in adolescence or in life,
such as Duchenne's affecting early childhood and Becker
ans Emery-Dreifuss affecting in the teenage years.
And the majority of cases actually
have a positive family history
but there are cases of no family history in which
here the patient has a spontaneous gene mutation.
Now Duchenne muscular dystrophy is
caused by the absence of dystrophin,
a protein that is important in muscle health.
The symptoms generally begin between ages 3 and 5
and are characterized clinically by frequent falls,
difficulty running, difficulty
jumping and climbing stairs.
The patient will have a waddling gait,
you can see them walking on their toes,
and they will have enlarged calf muscles but these
is called 'pseudohyperthrophy of the calves'
because these are not muscles.
It is the loss of muscle and the
replacement of that area with fat.
So it is thus then
pseudohypertrophy of the calves.
Now many of these diseases have an
X-linked recessive inheritance pattern,
which is why they primarily affects
males and girls can be carriers.
But in rare cases, females can
be actually be affected by the condition.
Now there is no known treatment and death
unfortunately generally occurs in teenage years
for Duchenne muscular dystrophy due to muscular
involvement of the heart and respiratory muscles.