A myasthenic crisis (MC) is a potentially fatal condition which requires intensive care and is associated with respiratory failure due to muscle weakness, caused by the autoimmune disorder myasthenia gravis (MG).
Prior to having MC, patients with MG most often display increased generalized weakness. One study indicated that 76% of patients that had MC displayed signs of generalized asthenia before the attack . Other signs of an impending MC in MG patients include bulbar weakness and decreased strength of the respiratory muscles, which in one study occurred in 19% and 5% of patients, respectively . Unfortunately, the generalized symptoms displayed by patients prior to MC may hide the underlying breathing issues, which is the primary concern in these patients. Respiratory symptoms may be sudden, leading to abrupt respiratory failure, or gradual, where patients experience a relative increase in respiratory weakness compared to other muscles. Rarely, patients with MC will present with only respiratory failure  .
The respiratory failure associated with MC is often serious enough to require intubation. Patients who experience MC during surgery should remain intubated if respiratory failure persists after surgery is completed. If a patient who has not been diagnosed with MG present with MC, diagnosis of MG should be established, using physiological or immunological assays, to rule out other causes of respiratory failure. Imminent ventilation failure can be verified using lung function tests and diagnosis of MC can be confirmed in patients with MG using single-fiber electromyography or repetitive motor neuron stimulation. Edrophonium tests should be avoided due to the chances of increasing muscle fatigue.
MC requires intensive care, including ventilation, to address respiratory failure and should be treated with immunoglobulin (Ig) administration or plasma exchange (PE)  . Ig should be administered intravenously each day for five days at a dose of 400 mg/kg  concurrently with high doses enteral administration of corticosteroids (eg. prednisone 1-1.5 mg/kg/day). PE to treat MC involves the administration of 1 volume of plasma (approximately 3-4 L) every other day for 10 days (5 exchanges total) . High-dose corticosteroids should also be administered with PE and fluids can be replaced with normal saline supplemented with five percent albumin  . Patients who cannot tolerate corticosteroids may be administered cyclosporine although cyclosporine requires at least a month to produce desired effects  . Patients who experience MC that have pneumonia should be closely monitored due to their increased risk of developing aspiration pneumonia because of their immune suppressed state . If patients develop an acute MG attack, plasmapheresis to remove autoantibodies may be performed.
Patients that develop MC in developing countries, without access to intensive care units, have a severely decreased survival rate. One study on outcomes of MC in developing countries revealed that patients who were treated in an intensive care unit had a 100% survival rate whereas only a 50% survival rate was observed in patients that did not receive intensive care. Most patients with MC that receive a thymectomy display a partial reduction in symptoms and 35% of patients no longer experience any symptoms , therefore, if possible patients with MC should receive a thymectomy after puberty .
The mortality rates associated with MC have dramatically declined over time from a 75% mortality rate in the mid-1900s to only 5% since the 1990s    . This decline in mortality is due to improvements in therapy along with better intensive care. Although mortality rates have dropped significantly, patients who experience MC have considerable morbidity due to this condition.
A number of factors have been identified as contributors to a myasthenic crisis, although this condition may spontaneously occur in patients with MG   . The most common precipitating factor is an infection in patients with MG  . Other contributing factors include surgery, reducing immunosuppressives, pregnancy, elevated body temperature, hyperthyroidism, stress, drugs or medications associated with weakness and drug withdrawal. Medications that may increase weakness in patients with MG include medications for dysrhythmia (beta-blockers, quinidine, procainamide), specific antibiotics (tetracycline, macrolides, aminoglycosides, fluoroquinolones, chloroquine), muscle relaxants and some antipsychotic drugs    .
Of all patients with MG, approximately 10 to 20 percent will develop a myasthenic crisis and this will be the first sign of MG in roughly 13 to 20 percent of patients         . Each year close to three percent of individuals with MG experience such a crisis . Patients diagnosed with MG who develop a myasthenic crisis will generally have this condition soon after diagnosis (median time around 8 months to one year after diagnosis)  . Myasthenic crises are two times more likely to occur in women than men with the highest incidence in women between the ages of 30 to 50 years old. The age of onset of MC follows a bimodal distribution with early onset mainly affecting women and late onset occurring at similar levels in both genders   .
MG is an autoimmune disorder most commonly associated with autoantibodies against the acetylcholine receptors (AChR-MG) found at the motor end plate of the neuromuscular junction. Decreased sensitivity of skeletal muscles to acetylcholine occurs through direct blocking of the acetylcholine receptors by antibodies and through the accumulation of immune complexes and activation of complement at the motor end plate. Due to the decreased numbers of available AChRs and other changes at the motor end plate caused by inflammation, normal levels of ACh aren't sufficient to reach the threshold necessary to induce an action potential. Therefore, neural impulses that would normally induce muscle contraction in healthy individuals may fail to produce a response in individuals with MG. This causes muscle dysfunction and subsequent weakness in patients with MG. MC is a health crisis that may occur in patients with MG associated with a weakening of the muscles needed for respiration leading to respiratory distress. There are two distinct types of active MG with the most common type characterized by the presence of AChR-MG autoantibodies. The majority of studies focus on patients with AChR-MG autoantibodies. MG may also occur due to passive immunity when AChR-MG autoantibodies are passed through the placenta leading to neonatal MG. Neonatal MG caused by the passive immunity should resolve on its own.
Around 50% of patients with MC will not present any precipitating factors, however, factors, such as infection, should be identified and treated quickly if present. Patients with MG can do a number of things to decrease the risk of developing MC including, closely following a physician’s instructions regarding the use of anticholinesterases which will help to strengthen breathing muscles and prevent aspiration of food. Patients should maintain optimal nutrition to sustain strength and reduce stress. During exercise, rest should be taken intermittently. Medications that negatively affect MG should be avoided especially in individuals who have infections of the respiratory tract.
A myasthenic crisis is a condition characterized by respiratory failure in patients with myasthenia gravis . In MG, patients have generalized muscle weakness due to the presence of acetylcholine receptor (AChR) autoantibodies which target the motor end plate through direct inhibition of AChRs or by recruiting immune cells, thereby disrupting neuromuscular transmission. During MC, the already weakened muscles of individuals suffering from MG are severely incapacitated to the point where a respiratory failure occurs. Patients suffering from MC will need to be intubated and require mechanical ventilation. 15-30% of patients with MG will experience a myasthenic crisis   . Moreover, the patients may also develop quadriparesis and severe weakness of the oropharyngeal muscles during the crisis   . The crisis itself is often activated by an infection that stimulates the immune response.
The typical immunotherapy administered to treat a myasthenic crisis includes steroids, immunoglobulins and plasma exchange, which have helped to decrease the mortality rate of this serious disease to below 5%   .
Patients with myasthenia gravis may develop myasthenic crisis, which is a life-threatening condition associated with respiratory failure, that requires intensive care. Respiratory failure in MC is caused by weakening of the respiratory muscles, such as that of the diaphragm and chest muscles and this condition has to be treated with a ventilator. Approximately 15-20% of patients affected with MG develop MC. During MC, patients often experience extreme weakness of the legs and arms followed by the respiratory failure. Causes of MC include infection, stress, surgery or failure to take medications for MG. Along with ventilation in extreme cases of MC, patients may require treatment with immunoglobulin or plasma exchange along with corticosteroids.