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Myopathy Junction and Dystrophinopathies

by Carlo Raj, MD
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    00:01 To put things into perspective, where are we at this point? We’re at the myopathies.

    00:06 Look where we are.

    00:08 So, we’ve come out of the anterior horn.

    00:09 The motor would walk through the peripheral neuropathies, walk through neuromuscular junction diseases, and now we’re looking at myopathies.

    00:17 Skeletal muscle disorders.

    00:19 Myopathy.

    00:20 Myopathy is nonspecific, what does it mean? It just means disease of the skeletal muscle.

    00:24 You’d be very, very specific about the definition here, please.

    00:28 Versus dystrophy.

    00:30 We’ll get into muscular dystrophy.

    00:32 What does that mean to you? Hereditary.

    00:34 Under hereditary, we’ll then walk into, obviously, Duchenne, and we’ll also take a look at Becker muscular dystrophy.

    00:40 And I will tell you though, it doesn’t always have to be or have to be associated with the dystrophin gene.

    00:46 It could be, and that’s where our focus shall be.

    00:49 But to be technical, it doesn’t have to be, but, but hereditary is important.

    00:55 Myositis, what does that mean? It means that the muscle is undergoing inflammatory process.

    01:00 Allow the name to speak to you, -itis.

    01:04 Skeletal muscle disorders.

    01:06 We’ll walk through muscular dystrophy, channelopathy is important for us, mitochondrial myopathy, you've heard of MELAS.

    01:12 If you haven’t, it’s okay. I’ll walk you through it.

    01:14 Distal myopathies, inflammatory myopathies, and finally, we’ll end by looking at our endocrine drug and toxic myopathies, just a few words there.

    01:23 Let’s begin.

    01:25 Under muscular dystrophy, we’ll take a look at dystrophinopathies.

    01:29 Under dystrophinopathies, we have Duchenne, DMD, muscular dystrophy.

    01:33 We’ll talk about that in great detail.

    01:35 Becker muscular dystrophy, we’ll talk about that in great detail.

    01:40 These are dystrophies.

    01:40 What does that mean to you? Hereditary.

    01:43 Limb-girdle muscular dystrophy.

    01:45 It’s taken on quite a bit of prominence, so therefore, I must discuss it.

    01:50 And then finally, myotonic dystrophy.

    01:51 As rare as it may be, once again, it appears, trust me, on the wards and the boards.

    01:59 So, good stuff to come, let’s go.

    02:02 Under dystrophinopathies, how do we begin in general? Proximal weakness, including neck flexors.

    02:08 Usually, it will spare the ocular and bulbar.

    02:12 Pseudohypertrophy of the calves.

    02:14 What the heck does that even mean? It means that you’re going to develop or accumulate -- Think about where you are.

    02:20 Your lovely calves, okay? It looks big.

    02:24 Oh, that’s sexy, but what’s going on? It’s not muscle, it’s pseudohypertrophy.

    02:29 What the heck is filling it up? Fibro fat, okay? Fibrofatty changes, pseudohypertrophy.

    02:36 It’s a lot worse than we think.

    02:38 I’m being a little silly there, but seriously, this is no joke for the patient.

    02:43 Gower’s sign.

    02:45 With this dystrophinopathy, it’s especially Duchenne.

    02:47 We have a patient that is not even able to get up by himself.

    02:51 And so therefore, they have to then do what? Climb up their legs, huh? They climb up their legs using their arms.

    02:59 It’s called Gower’s sign.

    03:02 And relentlessly progressive.

    03:05 We have to talk about that dystrophin gene, won’t we? Because it is the anchor for your skeletal muscle.

    03:10 Associated cardiomyopathy, that is a huge point.

    03:14 At some point in time, if you lose your dystrophin, not only are you going to lose the ability to conduct yourself in your skeletal muscle but the heart muscle is also going to be effective.

    03:24 So you’ll have cardiomyopathy, no doubt.

    03:26 And unfortunately, respiratory insufficiency may lead to ultimately the death to your patient.

    03:33 But cardiomyopathy is right up there, isn’t it? Under dystrophinopathy.

    03:39 So both DMD, also Duchenne, and Becker muscular dystrophy, or due to different mutations of the dystrophin gene.

    03:48 That’s the only thing that they have in common.

    03:50 Is that clear? The only thing that they have in common is that it’s a defect in the dystrophin gene.

    03:57 It’s on the X-chromosome.

    04:00 X-linked recessive.

    04:02 Labs: Marked elevated creatinine kinase, as you can imagine, because the muscle is involved.

    04:07 And it can be diagnosed with genetic testing to forego the muscle biopsy.

    04:12 That’s important.

    04:13 Here, if you’re suspecting high suspicion of your dystrophinopathy, either Duchenne or Becker, then you can forego the muscle biopsy, which is always nice, but genetically, it will tell you what’s going on.

    04:27 X-linked recessive, but then please understand, Duchenne will be more or less your frame shift type of mutation that you talked about in genetics.

    04:35 So, there’s absolutely no dystrophin, there’s absolutely no dystrophin.

    04:41 So therefore, with Duchenne, your patient is going to present extremely young.

    04:45 By the time your patient is 15, 18, 20, he is already -- why did I say he? Take a look at the inheritance pattern, X-linked recessive, right? The male has one X, and if that X is diseased, boom, the man has it or the young adult has it.

    05:05 And by the time he is 18 or 20, wheelchair bound.

    05:12 Treatment: Management is going to be supportive only.

    05:14 And if you’d take a look at the Mendelian type of inheritance in this schematic, you’ll notice here that X-linked recessive, we have the male that is going to be affected quite a bit.

    05:24 In order for the female, obviously, both Xs have to be affected, and then you can be a trait, obviously, in a female.


    About the Lecture

    The lecture Myopathy Junction and Dystrophinopathies by Carlo Raj, MD is from the course Polyneuropathy. It contains the following chapters:

    • Myopathy Junction
    • Dystrophinopathies

    Included Quiz Questions

    1. Charcot Marie tooth disease
    2. Duchenne dystrophy
    3. Limb-girdle dystrophy
    4. Myotonic dystrophy
    5. Becker dystrophy
    1. Fibrofatty tissue accumulation
    2. Muscle hypertrophy
    3. Nerve enlargement
    4. Inflammation and edema
    5. Accumulation of blood
    1. Dilated cardiomyopathy
    2. Restrictive cardiomyopathy
    3. Hypertrophic cardiomyopathy
    4. Mitral valve prolapse
    5. Myocardial infarction
    1. X chromosome
    2. Chromosome 5
    3. Chromosome 16
    4. Chromosome 20
    5. Chromosome 3
    1. Frameshift mutation
    2. Point mutation
    3. Copy number variation
    4. Missense mutation
    5. Nonsense mutation

    Author of lecture Myopathy Junction and Dystrophinopathies

     Carlo Raj, MD

    Carlo Raj, MD


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