All the tests should be done and interpreted properly by a respiratory specialist with experience and understanding of neuromuscular disorders.


A sleep lab, is a good starting point. Most neuromuscular disorders will have some manifestations during sleep, even before there is evidence for significant impairment during the waking hours. The reason for that is that during sleep there is always some degree of relaxation of the respiratory muscles, and gas exchange is less effective.

It is very important to assess both oxygen saturation and CO2 level,during the test, as there are patients with significant respiratory muscle weakness who do not have sleep apnea and manage to keep levels of O2 within the normal to low range, and do have significant CO2 retention.


All the respiratory tests are based on the inhalation and exhalation of air into a special device that measures the volume of air, the flow rate, and the pressures.

The basic spirometry tests measure the amount of air that can be inhaled and exhaled during a normal deep breath, without resistance.

It is important to know that as those volumes are not only dependent on the force of respiratory muscles but are affected by other factors, such as the resistance of the chest wall etc. they can be misleadingly normal, during one single respiratory effort, such as is done in those tests, even in the face of significant clinically important respiratory muscle weakness.

Therefore it is important to directly assess the respiratory muscle force. This is done by inhaling and exhaling against a fixed resistance.

The MIP –Maximal Inspiratory Pressure, gives a good idea of the general respiratory muscle strength.
The MEP-Maximal Expiratory Pressure, gives more indication as to the intercostal muscles.
Snif-is a better measurement of the diaphragmatic strength, and as it is the only test done by nose breathing it is more accurate then the others in patients with significant facial muscle weakenss.

As the hallmark of myasthenia is muscle fatigue and not muscle weakness, it is very important to assess the endurance as well. this is done by the MVV test, which checks the amount of air that can be breathed during repeat effort, as opposed to the single effort done in the standard spirometry tests.

The results of all those tests taken together should give a good general idea of the degree of respiratory muscle involvement (if any)

Oxygen saturation can be in the normal range or slightly lower, even in patients with significant respiratory muscle weakness, and is not a good parameter to follow alone in MG..

Patients with MG do not usually have a significant oxygenation problem, unless nearly paralyzed or have another respiratory complication, and most do not require supplemental oxygen.

In conclusion:

We suggest that every patient with generalized MG will have a full respiratory evaluation at least once.
In case that there is no significant respiratory muscle involvement it would give a good baseline for further follow up in case respiratory symptoms do occur at a later stage. This is important as the normal values of respiratory tests can differ among people, and therefore early recongnition of respiratory muscle involvement is only possible if the normal for that person is known, by showing a trend of worsening even if still within the low normal range.
If there is a significant involvement of the respiratory muscles this will allow proper assessment of its severity, and the need for respiratory support.

Patients that have symptoms suggestive of respiratory muscle weakness, should have a repeat evaluation if the first one is non-conclusive, as it may show a trend, and be more informative the second time.

Although all those tests are effort dependent, most patients can perform them very well, after given proper explanation . therefore abnormal results in a patient with respiratory symptoms should not be interpreted as lack of effort during the test, unless there is clear evidence that the patient is not able or is unwilling to co-operate.

Patients with depression, chronic fatigue etc. have normal or near normal respiratory tests, as it does not require significant motivation or effort.