B2W2 Trans Phys Flashcards
Myasthenia Gravis
Autoimmune disorder caused by antibodies attacking the AChrs at the neuromuscular junction
Pathophysiology of T-Cells binding to AChr
Activates complimentary membrane attack complexes
Decreases AChr’s effectiveness
Directly blocks AChr’s
Non T-Cell MG
Caused by MuSK and LRP4
Symptoms of MG
Initial signs may be droopy lids, double vision, and bulbar weakness.
Main symptom is generalized muscle weakness which worsens throughout the day but improves with rest
Diagnoses of MG
Tensilon Test, AChr antibody serum test, MuSK serum test, and electrodiagnostic studies
Electrodiagnostic studies
Nerve and Needle test, Slow repetitive nerve stimulation, and single fiber EMG
Repetitive Nerve Stimulation
Slow RNS is used because it allows for the depletion of Primary ACh stores without the accumulation of Ca2+ in the presynaptic terminal
In about 60% of MG patients EPP will begin to decrease.
Slow RNS in NMJ defect determinants
A 10% difference in amplitude between the 1st and 4th response
Tensilon Test
Administration of an Acetyl Choline Esterase inhibitor prevents the ACh in the synaptic cleft from degrading which allows for more ACh to bind to receptors
~90% MG Patients
AChR Serum Antibodies
Detects the presence of AChR Antibodies in MG Patients
80% in Generalized MG Patients
55% in Ocular MG Patients
MuSK Antibodies
If AChR antibody test is negative MuSK is searched for instead.
Mainly Bulbar symptoms and not as many eye and limb symptoms
Single Fiber EMG
Most Sensitive test for the presence of an NMJ defect, but not specific. Used if slow RNS in non conclusive.
Voluntary SFEMG
Most widely used requires patient participation. Patient contracts muscle fiber
Stimulation SFEMG
Nerves are stimulated without the need for patient participation
Chest Imaging
CT/MRI used to determine the presence of a thymoma or thymus gland tumor
Thymic hyperplasia
Enlarged thymus gland. Removal is recommended
Myasthenia Exacerbation
Worsening symptoms without the need for intubation
Myasthenia Crisis
Sever worsening of respiratory symptoms.
Requires incubation
Causes of Myasthenia Crisis
Infection
Medication
Uncontrolled Disease
Stress
Inpatient Treatment for MG
Difficulty breathing/swallowing
Moderate to severe exacerbation
Myasthenia Crisis
Outpatient Treatment for MG
Pyridostigmine (Mestion) - Oral medication AChE inhibitor
Prednisone - Most common medication used for MG
Steroid Sparing Immunosuppressants (Cyclosporine) - Good in long term but takes time to work
Thymectomy - Thymus removal
Absolute Contraindications (Life Threatening for MG patient)
Curare and Botox
Both cause paralysis which is not what you need when your muscles are weak
Contraindications (Should Avoid for MG patients)
Antibiotics (Z-packs, Ciprofloxacin)
Anti-arhythmics
Magnesium
Antimalarials
Use with caution for MG patients
Antihypertensives
Lithium
Statins
Inpatient Treatment for MG
Airway assistance, cardiac monitoring, discontinue offending drugs, treat infection, and provide prophylaxis
Specific Treatment
Rescue Therapy
Removal of 1-1.5x plasma volume on each session for 3-5 sessions
Intravenous immunoglobulin for 5 days
Lambert Eaton Myasthenic Syndrome (LEMS)
Presynaptic NMJ disorder where the antibodies attach P/Q type voltage gated Ca2+ channels
LEMS Symptoms
Similar symptoms to MG but muscle weakness improves with exercise
LEMS Physical Exam
Proximal muscle weakness - muscles improve with repeated usage
Areflexia - muscles do not respond to stimuli
Dyspnea/dysphagia - shortness of breathe and trouble swallowing
Ataxia - lack of coordination
LEMS Diagnostic Testing
Anti P/Q type voltage gated calcium channel serum antibodies. 85-90% LEMS patients
Rapid Repetitive Nerve Stimulation (20-50 Hz) - Increase mobilization of ACh Stores
Rapid RNS
20-50 Hz
Promotes accumulation of Ca2+ in the presynaptic cleft promoting ACh release
In presynaptic defects EPPs do not reach threshold at baseline
LEMS Treatment
3,4 diaminopyridine - K+ Channel blocker which prevents hyperpolarization which prolongs depolarization thus increasing the Ca2+ entry
Botulism
A neurotoxin usually obtained from home canned food or unpasteurized honey
Botulism Symptoms
24-36 hours Severe facial weakness
Oculobulbar weakness
Slurred Speech
Descending weakness
Botulism Pathophysiology
At the presynaptic neuron of the NMJ botulism toxin cleaves SNARE proteins preventing vesicle fusion with the cell membrane
Less ACh is released resulting in a smaller CMAP
Exercise will improve CMAP
Unique Botulism Symptom
Fixed Pupillary Dilation
LEMS Vs. Botulism
LEMS repeated stimulation causes EPP increase of 150-300%
Botulism repeated stimulation causes mild EPP increase of 50-200%
