Neuromuscular Junction Disorders: Clinical Features and Pathophysiology

by Roy Strowd, MD

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    00:00 And again, when we evaluate patients, we're thinking of the distribution.

    00:05 Where are the problems? Where does this weakness occur? We should see presence of bulbar findings.

    00:11 And the presence of ptosis, diplopia, dysarthria, and dysphasia point towards a neuromuscular junction etiology.

    00:19 Sensory findings are normal.

    00:21 Reflex examination often shows normal reflexes.

    00:24 And we're looking for that wildcard symptom the presence of fatigability.

    00:28 Symptoms that worsen when muscles are contracted.

    00:32 After our first step is, to localize to the neuromuscular junction, we move to step two.

    00:37 What is this junctional disorder? And we can walk through the types of problems that pathophysiologic processes that occur in the body.

    00:45 We can look for immune disorders.

    00:47 And the immune disorder at the neuromuscular junction is called Myasthenia gravis.

    00:51 We can look for infections.

    00:53 And the primary infection to effect the neuromuscular junction is botulism.

    00:57 It has a tropism and affinity for the neuromuscular junction.

    01:02 The neoplastic or paraneoplastic disorder that affects the neuromuscular junction is called Lambert-Eaton myasthenic syndrome.

    01:09 Toxins and metabolic problems can also affect the neuromuscular junction.

    01:14 And there are specific drugs that we need to think about that can cause problems in the neuromuscular junction.

    01:20 And then there are some inherited and congenital problems.

    01:23 Congenital Myasthenia, and Neonatal myasthenia that can also affect the neuromuscular junction.

    01:29 We're going to walk through each of these disorders in subsequent lectures.

    01:33 But right now, I want you to know that those are the conditions that we should focus on when we're dealing with a problem or a patient who presents with neuromuscular junction signs and symptoms.

    01:43 So let's look at where those occur.

    01:45 We said junctional disorders should be broken down into presynaptic and postsynaptic disorders, where to each one of those fall.

    01:52 Well, Myasthenia gravis the most common junctional disorder and one that we really need to know is a postsynaptic problem.

    01:58 This disorder results from problems abnormality with the postsynaptic acetylcholine receptor.

    02:06 Anesthetics affect the postsynaptic action of acetylcholine binding to that postsynaptic acetylcholine receptor and muscle depolarization.

    02:15 Lambert-Eaton Myas Syndrome.

    02:17 Myasthenic syndrome is an important cause of a presynaptic junctional disorder.

    02:21 Antibodies to the presynaptic voltage-gated calcium channels prevent that influx of calcium and the communication can't proceed down the presynaptic terminus into the junction.

    02:34 Botulism is a disorder and infection that affects the binding of the vesicles to the presynaptic membrane.

    02:40 And so this is also another important presynaptic junctional disorder.

    02:44 And then lastly, cholinestarase inhibitors affect that cholinestarase enzyme in the synaptic cleft.

    02:51 So again, I want you to know about the important presynaptic and postsynaptic disorders that affect the neuromuscular junction.

    About the Lecture

    The lecture Neuromuscular Junction Disorders: Clinical Features and Pathophysiology by Roy Strowd, MD is from the course Disorders of the Neuromuscular Junctions.

    Included Quiz Questions

    1. Anesthetics typically work at the presynaptic terminal.
    2. Lambert-Eaton syndrome is due to antibodies against presynaptic calcium receptors.
    3. Myasthenia gravis is due to antibodies at the postsynaptic receptor.
    4. Botulism is due to disruption of presynaptic vesicle binding.
    5. Cholinesterase inhibitors work within the synaptic cleft.
    1. Trauma/injury
    2. Autoimmune/inflammatory conditions
    3. Infections
    4. Neoplastic/paraneoplastic syndromes
    5. Toxic/metabolic conditions

    Author of lecture Neuromuscular Junction Disorders: Clinical Features and Pathophysiology

     Roy Strowd, MD

    Roy Strowd, MD

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