Not to be confused with Myasthenic Syndrome (Eaton-Lambert syndrome)

Succinylcholine RESISTANT – may require a higher dose

Nondepolarizing muscle relaxants SENSITIVE – Consider a lower dose and anticipate prolonged duration.  Titrate carefully (suggested 1/2 – 2/3 of maintenance doses)

Muscarinic agonists – avoided/contraindicated. These drugs are especially dangerous in those taking anticholinesterases (most of these patients)

Induction – Short acting anesthetics such as propofol may have accentuated respiratory affects.  Tracheal intubation can often be accomplished without neuromuscular blockers.  Volatile anesthetics are also suggested as having relaxant affects that may be sufficient for tracheal intubation without neuromuscular blockers.

Watch for respiratory weakness – This condition is characterized by marked periods of exacerbation and remission.  Prompt weakness with exercise/physical effort.  Stress, hyperthermia, electrolyte abnormalities, antibiotics (particularly aminoglycosides), pregnancy, and surgery may also precipitate weakness. The lingering effects of opioids and their affect on respiratory function detract from their use during maintenance of anesthesia. Do not extubate unless demonstrating adequate spontaneous ventilation.

Delayed weakness – Respiratory function may appear to be adequate in the early postoperative period but may deteriorate after a few hours.  Be ready to reintubate if needed.

Airway exam – Dysphagia, dysarthria, and difficulty with oral secretions can be present, so be sure to assess.  This makes them particularly susceptible to pulmonary aspiration.  Optimize respiratory strength and function preoperatively.

Plasmapheresis – If vital capacity is < 2L (normal is ~ 4.6L), plasmapheresis can be performed prior to surgery to improve postoperative respiratory function.

Full disclosure – Make sure to preoperatively inform the patient that they may wake up intubated if postoperative respiratory function is not adequate.

High risks for arrhythmias – be alert for atrial fibrillation, heart block, or cardiomyopathy.

Pregnancy – 20-40% of parturients with this condition have enhanced/worsened symptoms. Children born to mothers with myasthenia gravis sometimes have transient muscle weakness.  This usually presents within 24 hours.  This will be characterized by general muscle weakness and expressionless facies.  These newborns can progressively get weaker until intubation is required.

Most common disease to affect the neuromuscular junction.

This is the most common disease known to result in respiratory failure due to alterations in neuromuscular transmission.

Affects 1:7500, primarily women 20-30 years of age. Men that have the condition are usually > 60 years of age.

Autoimmune disorder caused by acetylcholine receptor-binding antibodies, which results in the destruction of the postsynaptic acetylcholine receptors at the neuromuscular junction.

Thymus is suggested as the source of the antibodies, but it is still uncertain.

Results in severe muscle weakness (asymmetrical) without atrophy.

First signs include weakness of extraocular muscles (diplopia/ptosis).

Edrophonium (2-8 mg) produces brief recovery of muscle strength/function and may be used to diagnose myasthenia gravis.

Typically treated with anticholinesterase. Pyridostigmine is the most widely used. This treatment can result in a cholinergic crisis. Immunosuppressants (most commonly corticosteroids) are indicated if MG is not adequately controlled with anticholinesterases.

Thymectomy is also a common procedure to induce remission – though the full benefits of this procedure may not be realized for months.

IgG antibodies cross the placenta which causes weakness in ~20% of neonates born to patients with this condition.

Type I – symptoms confined to the extraocular muscles
Type IIa – slow progressing with no involvement of respiratory muscles. These respond well to anticholinesterase drugs and corticosteroids.
Type IIb – rapidly progressing, more severe, muscles of respiration possibly involved. Treatment with drugs is not as effective.
Type III – Acute onset and rapid deterioration within 6 months. High mortality.
Type IV – Severe muscle weakness that is a progression of type I or II.

Common co-morbidities such as thymic hyperplasia, thymomas and other autoimmune disorders such as hyperthyroid disorder, rheumatoid arthritis, and SLE (lupus) are very common.