Myasthenia gravis (MG) is a chronic autoimmune disease that reduces the muscle strength and the ability for the muscles to engage in repetitive muscle movements, these occur due to a problem in the neuromuscular junction.
Fatigue is extreme tiredness, lack of energy, and difficulty in concentrating in spite of adequate rest and nutrition. Muscle fatiguability is difficulty in initiation of muscle movement and/or sustaining that muscle movement. Fatigue is a very subjective feeling; there is no proper definition or parameter to identify the severity of it. Fatigue depends on certain physical and psychological factors; therefore, it is difficult to get an objective idea about fatigue when a patient complains of it. Fatigue can be either physical fatigue or mental fatigue or both. Chronic fatigue is the presence of fatigue above a certain limit for 6 months or more.
Does Myasthenia Gravis Cause Fatigue?
One study shows that 82% (from 28 patients) of myasthenia gravis patients complained of fatigue when compared with healthy individuals and half of these fatigue patients had mental fatigue along with physical fatigue which could be explained fully with muscle fatiguability.
In another study 82 patients from 36 complained of fatigue (44%) and this was compared to a control group of healthy individuals of 410 from whom only 22% complained of fatigue. This study conclude that myasthenia gravis patients had a higher total fatigue score and they also had more autonomic symptoms compared to the control group. (1)
Cause Of Fatigue In Myasthenia Gravis Patients
Fatigue is one of the commonest symptoms in myasthenia gravis. You might feel tired and reduced energy towards the latter part of the day, you feel more energetic when you wake up in the morning. Many myasthenia gravis patients complain of generalized fatigue, lack of energy and difficulty in concentrating but the clinical examinations did not show any muscle weakness in these patients. Even after the administration of Acetylcholine inhibitors (AChEI) with adequate rest, there was no improvement in the fatiguability. So, what can be the reason for this fatigue in myasthenia gravis patients?
Autonomic Dysregulation- The exact pathophysiology of fatigue that occurs in myasthenia gravis patients is not fully understood. Some studies of chronic fatigue syndrome have found out that fatigue can be due to autonomic dysregulations. The severity of myasthenia gravis can be associated with the autonomic symptoms. Some of the mechanisms of how autonomic dysregulations occur in myasthenia gravis patients are:
- Deficiency in the regulatory process of the sympathetic nervous system can give rise to autonomic dysfunction.
- Cholinergic autonomic nerves might be affected despite the absence of clinical autonomic symptoms and signs.
- Presynaptic impairment seen in myasthenia gravis can be the cause of this autonomic dysregulation.
- The medication AChEI can also contribute to the development of autonomic dysregulations and changes in the normal autonomic functions.
Studies have also found out that fatigue is associated with thermoregulation, orthostatism (erect position of the body) and sleep. The exact mechanism is not understood maybe all of the above mechanisms contribute in some way.
Overweight and obese myasthenia gravis patients also experience fatigue. Most of these patients were overweight due to the steroids they take for myasthenia gravis treatment. Overweight reduce their physical ability and causes fatigue.
Medication especially the AChEI can contribute to fatigue but there is no evidence to prove this theory. (1)
Fatigue is one of the common symptoms seen in myasthenia gravis patients; however, it is an underrecognized symptom as there is no specific definition or an objective parameter to test the fatigue and severity of fatigue. Fatigue in myasthenia gravis patients was related to the muscle fatiguability however, in most patients the clinical examinations did not show any muscle weakness and even after the administration of AChEI with adequate rest there was no improvement in the fatiguability. Therefore, now they believe there can other reasons for this fatigue and it is suggested that autonomic dysregulation can be one of the reasons. More evidence is needed to prove this theory. Other reasons include overweight and obesity leading to physical restriction and medication especially AChEI.
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