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Limb-Girdle Muscular Dystrophies and Channelopathies

by Carlo Raj, MD

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    00:01 Limb-Girdle Muscular Dystrophies - shoulder and hip as exactly the name implies.

    00:07 Shoulder and hip, shoulder and hip girdle weakness.

    00:11 Relative sparing once again of the ocular and bulbar and here cardiomyopathy is less frequent, so if you get a situation where you're suspecting muscular dystrophies and has nothing to do with dystrophin and in fact, if you're looking for dystrophin on your band and you find it, and you know how to interpret a band -- a band you literally you find a band and then you find coloration - and you find coloration for that particular gene, dystrophin, then it exist if the band is blank that means the dystrophin is not there.

    00:50 So if you find the dystrophin is present and you find issues with the shoulder and the hip and the girdle, then your diagnosis is Limb-Girdle Muscular Dystrophy.

    01:01 Cardiomyopathy, much less common.

    01:04 Pathophys here. Heterogeneous abnormalities of muscle-related proteins.

    01:10 It is going to be hereditary because this is a dystrophy.

    01:14 Labs here ones again elevated CK - creatinine kinase as you can imagine.

    01:19 May require muscle biopsy whoever for definitive diagnosis because the genetics here with dystrophin is not going to be clear cut.

    01:27 Management here will be supportive, be familiar with LG muscular dystrophy, please.

    01:35 In this illustration, what is being highlighted for you is the dystrophin and with the dystrophin you’ll notice here that this is the anchor for much of your muscle and if for whatever reason that dystrophin is not present, as in Duchene muscular dystrophy, your skeletal muscle could be affected and your heart muscle could be affected and please keep in mind that the respiratory system could be at serious risk of arrest.

    02:02 Here we’ll take a look at myotonic dystrophy.

    02:06 It’s the most common adult onset of muscular dystrophy, so once again, its inheritance, right? That’s what dystrophy means by definition.

    02:14 We have type I MD which is muscular dystrophy and this is called Steinert's disease and if its type II, it's called proximal myotonic myopathy, PROMM - distal weakness predominates and that’s important for you to pay attention to, huh? Distal weakness, so it already begin out here.

    02:35 The myotonia, state of increased muscle contraction and impaired relaxation is extremely important for you to understand.

    02:43 Myotonic, it mean to say that the muscle is in a sustained state of contraction, impaired relaxation.

    02:51 There's going to be frontal balding - that is a very, very important as a clinical feature.

    02:57 Cataracts, cardiac conduction defect and multisystem disease with myotonic dystrophy.

    03:04 We’ll talk a little bit more with myotonic dystrophy.

    03:07 Hatchet faces, at this point, frontal balding is good enough for you to know.

    03:14 Pathophys here, it’s a trinucleotide expansion.

    03:18 Let’s have a closer look at the pathophysiology of Type I Myotonic dystrophy.

    03:24 So here, the trinucleotide expansion that you hopefully have memorized is CTG Myotonic dystrophy, say it with me, CTG Myotonic dystrophy, you’ll never forget it.

    03:41 CAG Huntington, right? And there's a few more that you've learned about in genetics for sure such as CGG - I don’t want to get ahead of myself at this point, let's focus on myotonic dystrophy.

    03:59 What is trinucleotic expansion mean to you? Anticipation.

    04:02 On your labs normal or perhaps mildly elevated CK.

    04:07 DNA testing is available and on your EMG, myotonic discharges or what you're looking for, what does that mean to you? Increased muscle contraction with decreased ability to relax.

    04:21 Channelopathies. Think about all the different channels that are responsible for contractions? Sodium obviously will play a huge role.

    04:31 As episodic weakness due to muscle on channel defect - now, there are some famous athletes in baseball - there was a man from Orlando - I forgot his name but he had weakness and at some point in time the management got upset with him because they just thought that he was making stuff up but eventually came to be diagnosed with the channelopathy, so it does exist and actually its more common than what we think.

    05:00 All known or autosomal dominant and apart from sodium you also wanna keep in mind hyperkalemic periodic paralysis - due to a defect in the sodium channel and these two obviously would play a role always.

    05:15 Potassium obviously is going to play a role in establishing resting membrane potential and if for whatever reason there’s a sodium channel defect and if there’s hyperkalemia, well you know that you are going to raise your resting membrane potential towards your threshold which you’re messing up everything in terms of your sodium channel.

    05:32 That has to be -- that’s basic physiology. I can't really help you out there right now, right? So, if you're unfamiliar how to interpret hyperkalemia and what it does to resting membrane potential and how that then affects the sodium channel, guess what? Go back and review now so that when I’m talking to you it makes perfect sense.

    05:51 What about hypokalemic? Well, if it's hypokalemic, can I ask you? What happens to resting membrane potential? Good, it becomes hyperpolarized.

    06:02 It gets further away from your threshold - so guess what happens here? Periodic paralysis once again, due to a defect in sodium or your calcium channel.

    06:12 So all of these must play a role with channelopathies and whenever you deal with contraction obviously you’re dealing with potassium, sodium, and calcium.

    06:21 You have to, that’s how the body functions.


    About the Lecture

    The lecture Limb-Girdle Muscular Dystrophies and Channelopathies by Carlo Raj, MD is from the course Polyneuropathy. It contains the following chapters:

    • Myotonic Dystrophy
    • Channelopathies

    Included Quiz Questions

    1. Conduction defects
    2. Dilated cardiomyopathy
    3. Circulation defects
    4. Pericarditis
    5. Myocarditis
    1. Autosomal dominant
    2. Autosomal recessive
    3. X-linked dominant
    4. X-linked recessive
    5. Mitochondrial
    1. Ocular and bulbar muscles are relatively spared.
    2. Shoulder and hip muscles are not affected.
    3. Cardiomyopathy is frequently seen.
    4. X-linked recessive
    5. Decreased creatine kinase
    1. Sodium channel defect
    2. Potassium channel defect
    3. Defect in sodium and potassium channel
    4. Chloride channel defect
    5. Defect in voltage-gated calcium channels
    1. Myotonic dystrophy
    2. Limb-girdle muscular dystrophy
    3. Duchenne muscular dystrophy
    4. Becker muscular dystrophy
    5. Channelopathies
    1. CTG trinucleotide expansion
    2. CAG trinucleotide expansion
    3. GAA trinucleotide expansion
    4. CGG trinucleotide expansion
    5. GAG trinucleotide expansion
    1. Frontal balding
    2. Temporal balding
    3. Proximal weakness
    4. Argyll Robertson pupil
    5. Hypertrophic cardiomyopathy

    Author of lecture Limb-Girdle Muscular Dystrophies and Channelopathies

     Carlo Raj, MD

    Carlo Raj, MD


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