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cramps, early satiety and nausea) in an adult with studies have indicated that pyridostigmine decreases
MG associated with thymoma. These manifestations the resting heart-rate by about 5-7 beats/min and
improved by AChE-Is and thymectomy. Previous increases the R-R interval and long-term time-domain
studies rarely reported other autonomic nervous system indices of HRV in normal subjects [38] and patients
dysfunctions (sympathetic and parasympathetic) with heart failure. [39] However, none of these studies
in patients with MG [19-22] including gastrointestinal, reported marked reduction of SDNN below 50 ms or
intestinal pseudo-obstruction, [21,23] acute autonomic presence of VEs, SVEs or depresses ST-T as observed in
and sensory neuropathy and severe panautonomic this study. We suggested that although pyridostigmine
failure. [19,22] These studies reported increase in the could reduce HRV indices but the marked reduction
autonomic nervous system dysfunction with the severity observed in this study is attributed to the autonomic
of MG. Meanwhile improvement of both neuromuscular nervous system involvement by the disease process.
and autonomic symptoms was observed with AChE-Is
and after thymectomy. Furthermore, neurophysiological The results of this study indicate that patients with
tests and laboratory studies also confirm the presence of MG are considered at high risk due to the presence
autonomic dysfunction in patients with MG. For instance, of autonomic nervous system dysfunction and are
augmentation in epinephrine excretion, although the candidates for earlier considerations of cardioprotective
nor-epinephrine excretion remains unchanged or even medications. Thus, caution has to be considered for
undergoes reduction in response to forearm ischemia prescribing drugs that disturb the cardiovascular
or orthostasis (a sign of sympathetic deficiency), was autonomic nervous system and preanesthetic evaluation
reported in patients with MG, while both stimuli in before surgery. [40,41]
[24]
normal subjects induce a rise in norepinephrine urinary
excretion without significant changes in epinephrine Despite the strength of our findings, the main limitation
excretion. of this study is the small sample size. Longitudinal and
prospective studies are needed.
The exact mechanisms of the autonomic nervous
system dysfunction in patients with MG could rely In conclusion, patients with MG may have specific ECG
on the involvement of autonomic neuronal nAChRs abnormalities indicating subclinical cardiac autonomic
by an immune mediated processes of MG. [25,26] The dysfunction even in milder stages of the disease.
structural identities between different muscle and Depressed SDNN of HRV is an early warning sign
autonomic nAChRs subunits with the possibility of of autonomic neuropathy. These results indicate the
cross-reactivity between different nAChRs antibodies need for routine evaluation of autonomic functions
may be contributed as a cause of immune-mediated in patients with MG both to identify patients at high
autonomic neuropathy with MG. Additionally, a few risk for earlier consideration of cardio-protection and
studies reported myocarditis in patients with MG and long-term follow up studies.
suggested that cardiac involvement with MG could
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24 Neuroimmunol Neuroinflammation | Volume 2 | Issue 1 | January 15, 2015