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40 Cards in this Set

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An autoimmune disease characterized by muscle weakness and fatigue

Associated with other autoimmune diseases such as rheumatoid arthritis.
Myasthenia Gravis
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
The thymus gland is abnormal in the majority of these patients.
Myasthenia Gravis
What are some of the primary clinical manifestations with myasthenia gravis?
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
What are two major characteristics of Myasthenia Gravis?
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
There are no changes in these for a patient with Myasthenia Gravis?
Reflexes
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
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
Many patients with this type of MG do not improve with edrophonium or neostigmine
Many patients with MuSK antibody-positive MG do not improve with edrophonium or neostigmine
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)
Found in approximately 90% of patients with Thymomas and 1/3 of patient without Thymomas in MG.
Anti-Striational Muscle Antibodies
Antibodies specific to tyrasine kinase are identified in approximately ½ of patients who are AChR-Ab negative in MG.
Anti-MuSK Antibodies
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
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
“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
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
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
What are the Immunosuppressant drugs used to TX MG?
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
Drugs that should never be used in patients with MG are?
Alpha-interferon,
botulinum toxin,
d-penicillamine,
telithromycin
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
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
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
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
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
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
Isolated facial, oropharyngeal, cervical and upper limb weakness

No lower limb involvement
Pharyngeal-Cervical-Brachial Variant - Associated with GBS
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
What is a key difference between GBS and MG?
In GBS reflexes are absent early in disease progression
May include facial droop, diplopias, dysarthria, dysphagia

Facial and oropharyngeal weakness usually occur after trunk and limb involvement
Cranial Nerve Involvement in GBS
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
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
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
When performing EMG studies to diagnose GBS, changes should be present in at least how many nerves ideally in separate regions?
2, ie. upper limb and lower limb
Patients with GBS should receive prophylaxis for what?
DVT
When using narcotics in a GBS patient what should you be very careful to avoid?
Paralytic illeus or constipation
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.
What are some predicting factors for mechanical ventilation of a GBS patient?
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
What is used to TX GBS?
Intravenous Immunoglobulin (IVIG)

Plasmapheresis
TX for GBS

MOA: Blocks macrophage receptors, inhibits antibody production and neutralizes pathologic antibodies
Adult dosing: 2g/kg IV
Intravenous Immunoglobulin (IVIG)
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