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Myasthenia Gravis (Mind to Ground) (Differential Diagnosis (Immunologic…
Myasthenia Gravis (Mind to Ground)
2 Types
Ocular myasthenia gravis
Muscle weakness is limited to eyelids and extraocular muscles
Generalized myasthenia gravis
Muscle weakness involves a variable combination of
Muscles of the mouth and throat responsible for speech and swallowing
Limbs
Respiratory muscles
Neck extensor and flexor muscles are affected causing "Dropped head syndrome" AKA "bobble head"
Pathophysiology
Anatomic Alterations/AAAA
A
ccumulation of mucous
A
irway obstruction
A
lveolar consolidation
A
telectasis
Diagnostic Testing
Clinical presentation and history
See Clinical signs and symptoms list
Bedside tests
Ice pack test :red_flag:
Simple, safe, reliable procedure
Application of ice pack to its symptomatic eye for 3-5 mins
Positive for MG when improvement of ptosis of at least 2 mm
Edrophonium (Tension) test :red_flag:
Used with pt with ptosis or ophthalmoparesis
Edrophonium, a short-acting drug, blocks cholinesterase from breaking down ACh after is has been released from the terminal axon
Positive for MG when dramatic improvement in muscle function (lasting about 10 mins) is seen after administration
Immunologic studies :
Serologic tests are used to detect the presence of circulating acetylcholine receptor antibodies (AChR-Abs)
Binding AChR antibodies test is highly specific for MG :red_flag:
Electrodiagnostic studies
Repetitive nerve stimulation (RNS)
Most frequently used for MG
A progressive decline in the CMAP amplitude with the first 4-5 stimuli (detrimental response) > 10%
Single-fiber electromyography (SFEMG)
The most sensitive diagnostic test for MG
Increase variability time between action potentials
Differential Diagnosis
Chronic muscle fatigue, IMPROVING after periods of rest :red_flag:
Ptosis :red_flag:
Immunologic studies
Binding AChR antibodies is highly specific for MG :red_flag:
Electrodiagnostic studies :red_flag:
See electrodiagnostic studies list
In cases with ocular or bulbar symptoms, an MRI of the brain is indicated. CT scanning or ultrasound of the orbits is helpful in the differential diagnosis of ocular myasthenia and thyroid ophthalmopathy.
Lumbar puncture may be helpful in ruining out lymphomatous or carcinomatous meningitis in some cases
Bedside tests :red_flag:
See bedside test list
MG can also be confused with a stroke due to facial muscle weakness
Respiratory Management
Oxygen therapy
Bronchopulmonary hygiene therapy
Lung expansion therapy
Mechanical ventilation
Close respiratory monitoring
FVC
MIP
MEP
BP
SpO2
ABG
Impending acute respiratory failure requiring MV
FVC < 20mL/kg
MIP < -30cm H20
MEP < 40cm H20
PaCO2 > 45 mmHg
pH < 7.35
General management
Plasmapheresis
Intravenous immune globulin (IVIG)
Clinical Signs and Symptoms
Fluctuating skeletal muscles weakness, often with true muscle fatigue
Muscle fatigue will improve with rest :red_flag:
Facial muscle weakness:
Ptosis
(drooping of one or both eyelids :red_flag:
Diplopia
: Double vision
Ophthalmoplegia
: paralysis or weakness of one or more of the muscles that control eye movement
Difficulty
Breathing
Speaking
Chewing
Swallowing
Unstable gait
Weakness in arms, hands,finger,legs and neck
Tendon reflexes almost ALWAYS remain in tact
Myasthenia Gravis is the MOST COMMON disorder of the neuromuscular junction
It interferes with the chemical transmission of acetylcholine (ACh) between the axonal terminal and the receptor sites of voluntary muscles
Etiology
ACh receptor (AChR) antibodies (IgG antibodies) that block the nerve impulse transmission at the neuromuscular junction
Blocking the ACh from the receptor sites of the muscular cell
Accelerating the breakdown of ACh
Destroying the receptor sites