Myasthenia Gravis (Mind to Ground)

Myasthenia Gravis (Mind to Ground)

2 Types

Pathophysiology

Diagnostic Testing

Differential Diagnosis

Respiratory Management

Clinical Signs and Symptoms

Ocular myasthenia gravis

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

Fluctuating skeletal muscles weakness, often with true muscle fatigue

Facial muscle weakness: Ptosis (drooping of one or both eyelids 🚩

Muscle fatigue will improve with rest 🚩

Anatomic Alterations/AAAA

Accumulation of mucous

Airway obstruction

Alveolar consolidation

Atelectasis

Generalized myasthenia gravis

Muscle weakness is limited to eyelids and extraocular muscles

Muscle weakness involves a variable combination of

Muscles of the mouth and throat responsible for speech and swallowing

Limbs

Respiratory 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

Clinical presentation and history

Neck extensor and flexor muscles are affected causing "Dropped head syndrome" AKA "bobble head"

Bedside tests

Immunologic studies :

See Clinical signs and symptoms list

Chronic muscle fatigue, IMPROVING after periods of rest 🚩

Ptosis 🚩

Immunologic studies

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

Ice pack test 🚩

Simple, safe, reliable procedure

Edrophonium (Tension) test 🚩

Serologic tests are used to detect the presence of circulating acetylcholine receptor antibodies (AChR-Abs)

Application of ice pack to its symptomatic eye for 3-5 mins

Positive for MG when improvement of ptosis of at least 2 mm

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

Binding AChR antibodies test is highly specific for MG 🚩

Binding AChR antibodies is highly specific for MG 🚩

Electrodiagnostic studies

Repetitive nerve stimulation (RNS)

Single-fiber electromyography (SFEMG)

Most frequently used for MG

The most sensitive diagnostic test for MG

Electrodiagnostic studies 🚩

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

A progressive decline in the CMAP amplitude with the first 4-5 stimuli (detrimental response) > 10%

Increase variability time between action potentials

Bedside tests 🚩

See bedside test list

Oxygen therapy

Bronchopulmonary hygiene therapy

Lung expansion therapy

Mechanical ventilation

Close respiratory monitoring

FVC

MIP

MEP

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)

MG can also be confused with a stroke due to facial muscle weakness