3-year-old (male) with walking difficulties

by Mohammad Hajighasemi-Ossareh, MD, MBA

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    00:02 A 3 year old boy presents to the office with his mother.

    00:05 She states that her son seems weak and unwilling to walk.

    00:09 He learned to walk recently and had notable developmental delay.

    00:15 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.

    00:23 A genetic study is performed that reveals an absence of normal functioning dystrophin.

    00:28 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.

    01:01 Now let's jump into this question together.

    01:04 The first thing we need to do is determine what kind of subject we're dealing with.

    01:07 Now this is a condition of pathology and the organ here seems to be the musculoskeletal system.

    01:12 So this is muscoloskeletal pathology.

    01:15 So this is a 2-step question.

    01:17 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.

    01:25 And the stem is absolutely required to understand the genetic study results and also the clinical history and exams of the patient.

    01:33 Now let's walk through this question together.

    01:35 The first thing we need to do is understand what are the symptoms that are actually suggestive of an inherited muscular dystrophy.

    01:42 Now muscular dystrophy is characterized by progressive weakness and loss of muscle mass.

    01:47 And the symptoms of most common types of muscular dystrophy actually begin in childhood and are most commonly seen in males.

    01:55 And the majority of cases have a positive family history.

    01:58 But there are of course cases in which no family history is present and that is due to a spontaneous gene mutation.

    02:04 So it appears from this case that the patient does have progressive weakness, loss of muscle mass.

    02:09 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.

    02:20 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.

    02:35 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.

    02:45 Now let's refer to the image to help us understand why it's important.

    02:49 So this image shows the pathophysiology of Duchenne's muscular dystrophy.

    02:53 As we can see above, we have a muscle, and then the muscle fiber.

    02:58 There we have the extracellular matrix, a membrane protein complex, and dystrophin which connects the actin to the actual cell membrane.

    03:09 And it is dystrophin that actually converts the actin and myosin filaments to the cell membrane.

    03:16 And the absence of dystrophin will cause muscle wasting and weakness in muscle function.

    03:22 Thus in this case, the answer choice for this patient, or in this case is Duchenne muscular dystrophy or answer choice (A).

    03:32 Now let's look at some of the other answer choices.

    03:34 Now, Becker msucular dystrophy, which some people consider as 'milder' Duchenne is unlikely as these symptoms generally begin in the teenage years.

    03:45 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.

    03:55 Myotonic muscular dystrophy is also unlikely as facial and neck muscles are usually affected first - not the case here.

    04:02 And Emery-Dreifuss muscular dystrophy is unlikely as this presentation is generally seen in teenage years as well.

    04:09 Let's review some high-yield facts regarding muscular dystrophy and Duchenne muscular dystrophy.

    04:14 Now the group of diseases that are characterized as progressive weakness and loss of muscle is called muscular dystrophy.

    04:21 And the condition is cause by gene mutation that interfere with the production of key proteins for muscle health.

    04:28 Now there are several different types of muscular dystrophy, many of which are mentioned in the question answer choices.

    04:33 But the most common form is Duchenne muscular dystrophy which currently affects roughly 1 in 3500 males.

    04:41 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.

    04:55 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.

    05:05 Now Duchenne muscular dystrophy is caused by the absence of dystrophin, a protein that is important in muscle health.

    05:12 The symptoms generally begin between ages 3 and 5 and are characterized clinically by frequent falls, difficulty running, difficulty jumping and climbing stairs.

    05:21 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.

    05:34 It is the loss of muscle and the replacement of that area with fat.

    05:38 So it is thus then pseudohypertrophy of the calves.

    05:41 Now many of these diseases have an X-linked recessive inheritance pattern, which is why they primarily affects males and girls can be carriers.

    05:52 But in rare cases, females can be actually be affected by the condition.

    05:56 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.

    About the Lecture

    The lecture 3-year-old (male) with walking difficulties by Mohammad Hajighasemi-Ossareh, MD, MBA is from the course Qbank Walkthrough USMLE Step 1 Tutorials.

    Author of lecture 3-year-old (male) with walking difficulties

     Mohammad Hajighasemi-Ossareh, MD, MBA

    Mohammad Hajighasemi-Ossareh, MD, MBA

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