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40 Cards in this Set
- Front
- Back
An autoimmune disease characterized by muscle weakness and fatigue
Associated with other autoimmune diseases such as rheumatoid arthritis. |
Myasthenia Gravis
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The post-synaptic muscle cell membrane is distorted
The concentration of Acetylcholine Receptors (AChRs) on the muscle endplate membrane is reduced AChR antibodies attach to the AChRs blocking Acetylcholine (ACh) binding Decrease ACh reduces the probability that a nerve impulse will be followed by a muscle action potential |
Pathophysiology of Myasthenia Gravis
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The thymus gland is abnormal in the majority of these patients.
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Myasthenia Gravis
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What are some of the primary clinical manifestations with myasthenia gravis?
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Asymmetrical ptosis or diplopia is the initial symptom in 2/3 of patients
Ocular Symptoms Become worse while reading, watching TV, driving Exacerbated by bright sunlight Difficulty chewing, swallowing or talking is the initial symptom in 16% of patients Limb or axial weakness presents first in approximately 20% of patients with MG |
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What are two major characteristics of Myasthenia Gravis?
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Fatigable Ptosis after 30 seconds of fixed gazed: Left eye > Right
Weakness of the jaw muscles as evidenced by spontaneous opening of the mouth. Myasthenia Snarl |
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There are no changes in these for a patient with Myasthenia Gravis?
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Reflexes
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Neck flexors are usually weaker than neck extensors
Deltoids, triceps, extensors of wrist and fingers and ankle dorsiflexors tend to be weaker than other limb muscles Sustained activity of the affected muscles increases weakness and results in muscle fatigue which improves after rest |
Clinical Manifestations of Myasthenia Gravis
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Temporary improvement in muscle strength following IV administration of the drug
Slows the breakdown of ACh by inhibiting Acetylcholinesterase Most reliable when improvement is seen with eyelid ptosis, ocular muscle weakness or dysarthria |
Edrophonium Chloride (Tensilon) Test in Myasthenia Gravis
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Many patients with this type of MG do not improve with edrophonium or neostigmine
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Many patients with MuSK antibody-positive MG do not improve with edrophonium or neostigmine
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The findings for this test may be normal in the first few days of Myasthenia Gravis.
Finding elevated antibodies in a patient with compatible clinical features confirms the diagnosis of MG. |
Acetylcholine Receptor Antibodies (AChR-ab)
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Found in approximately 90% of patients with Thymomas and 1/3 of patient without Thymomas in MG.
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Anti-Striational Muscle Antibodies
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Antibodies specific to tyrasine kinase are identified in approximately ½ of patients who are AChR-Ab negative in MG.
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Anti-MuSK Antibodies
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Diagnosis of MG
Abnormal with a reproducible 10% decrement in amplitude when comparing the first to the fourth or fifth stimulus Response usually more obvious in the proximal muscles: facial muscles, biceps, deltoids, trapezius |
Repetitive Nerve Stimulation
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Most sensitive clinical test of neuromuscular transmission
Shows increased jitter (variability) in affected muscles With ocular MG, jitter is abnormal in a limb muscle in 60% of patients With any degree of non-ocular muscle weakness, jitter is increased in the forearm extensor digitorum communis in 90% of patients |
Single Fiber EMG
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“Ice-Pack” Test: Cooling of a ptotic eyelid improves lid elevation
Meta analysis of six studies reported a sensitivity rate of 89% and high specificity for MG |
Ocular Cooling
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TX for MG
Slow the enzymatic breakdown of ACh at the cholinergic synapse so that ACh accumulates at the neuromuscular junction Neostigmine bromide Pyridostigmine bromide |
Cholinesterase Inhibitors
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Produces marked improvement or complete relief of symptoms in >75% of MG patients
Majority of the improvement occurs in the first 6-8 weeks of treatment Best responses occur in patients with recent onset of symptoms Patients with thymoma usually respond well Treatment usually starts with 1.5-2mg/kg per day until maximum improvement occurs; the dose is then tapered to the lowest amount to maintain improvement |
Prednisone
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What are the Immunosuppressant drugs used to TX MG?
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Azathioprine
May take 4-8 months for benefit to been achieved Cyclosporine Improvement usually begins in 2-3 months with maximum improvement being achieved after 6 months Cyclophosphamide Mycophenolate mofetil Improvement usually seen in 2-6 months Prednisone may be started with these drugs and then tapered or discontinued once the drugs have become effective |
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Drugs that should never be used in patients with MG are?
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Alpha-interferon,
botulinum toxin, d-penicillamine, telithromycin |
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Acute Inflammatory Demyelinating Polyradiculoneuropathy (AIDP)
Considered to be an autoimmune, antibody mediated syndrome Usually preceded by a triggering event, typically a bacterial or viral infection Manifests as a symmetric motor paralysis with or without sensory and autonomic disturbances |
Guillain-Barre Syndrome
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Usually preceded by a respiratory or gastrointestinal illness one to three weeks prior to onset
Campylobacter jejuni has been identified as the major causative organism Other infections: CMV-most common |
Pathophysiology of GBS
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Closely associated with C. jejuni infections
Pure motor symptoms with ascending symmetric paralysis Electrophysiologic studies are normal in sensory nerves, reduced or absent in motor nerves Recovery is usually rapid and prognosis is quite favorable |
Acute Motor Axonal Neuropathy (AMAN) - Associated with GBS
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Axonal degeneration of motor and sensory nerve fibers, little demyelination
Also associated with C. jejuni infection Usually a rapid and severe paralysis Associated with poorer recovery |
Acute Motor Sensory Axonal Neuropathy (AMSAN) - Associated with GBS
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Rapidly evolving ataxia, ophthalmoplegia and areflexia
Demyelination of CN III & VI, spinal ganglia and peripheral nerves Motor strength is usually spared Sensory loss is unusual but proprioception may be impaired Resolution usually occurs in one to three months |
Miller Fisher Syndrome - Associated with GBS
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Involves sympathetic and parasympathetic nervous systems
Cardiovascular involvement Blurry vision, dry eyes, anhidrosis Bowel and bladder retention Recovery is gradual and often incomplete |
Acute Panautonomic Neuropathy - Associated with GBS
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Isolated facial, oropharyngeal, cervical and upper limb weakness
No lower limb involvement |
Pharyngeal-Cervical-Brachial Variant - Associated with GBS
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Reflexes
Reflexes are absent early in disease progression Sensory Changes Paresthesias often precede the weakness Usually ascending and more pronounced in distal distribution seldom extending past the wrists & ankles Objective sensory findings on examination tend to be minimal |
GBS
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What is a key difference between GBS and MG?
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In GBS reflexes are absent early in disease progression
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May include facial droop, diplopias, dysarthria, dysphagia
Facial and oropharyngeal weakness usually occur after trunk and limb involvement |
Cranial Nerve Involvement in GBS
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Following things seen in GBS are what?
Tachycardia, Bradycardia, Facial Flushing, Paroxysmal Hypertension or Orthostatic Hypotension, Anhidrosis or Diaphoresis, Urinary Retention, Paralytic Ileus |
Autonomic changes
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Respiratory Involvement
Forty percent of patients have respiratory or oropharyngeal weakness Manifestations include: Dyspnea on exertion, SOB, difficulty swallowing, slurred speech Approximately 30% of patients will require mechanical ventilation |
GBS
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Diagnosis is usually based upon clinical features, cerebrospinal fluid examination and electrodiagnostic examination
In history, make sure to ask about any proceeding viral or bacterial infections. |
GBS diagnosis
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When performing EMG studies to diagnose GBS, changes should be present in at least how many nerves ideally in separate regions?
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2, ie. upper limb and lower limb
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Patients with GBS should receive prophylaxis for what?
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DVT
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When using narcotics in a GBS patient what should you be very careful to avoid?
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Paralytic illeus or constipation
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FVC <20mL per kg
Maximal Inspiratory Pressure <30cm H2O Maximal Expiratory Pressure <40 cm H2O Progression with reduction of >30% in VC, maximal inspiratory pressure or maximal expiratory pressure |
Indications to consider for intubation of a GBS patient.
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What are some predicting factors for mechanical ventilation of a GBS patient?
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Time from GBS onset to hospital admission of <7days
Inability to lift the elbows or head above the bed Inability to stand Ineffective cough Increased liver enzyme levels |
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What is used to TX GBS?
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Intravenous Immunoglobulin (IVIG)
Plasmapheresis |
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TX for GBS
MOA: Blocks macrophage receptors, inhibits antibody production and neutralizes pathologic antibodies Adult dosing: 2g/kg IV |
Intravenous Immunoglobulin (IVIG)
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TX for GBS
Removal of immunoglobulins and antibodies from the serum 3-5 exchanges of 50mL/kg of plasma IV over 1-2 weeks via central venous catheter |
Plasmapheresis
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