Your symptoms could be consistent with MG, although other muscle problems can cause neck weakness and eye muscle weakness such as mitochondrial myopathy, and certain congenital myopathies. Regular EMGs are commonly normal in
MG even if repetitive nerve stimulation is done - a more sensitive EMG for MG is a single fiber EMG, and this may be useful in determining a diagnosis. Blood test can be useful if postivive but if negative do not mean that MG is not there, a new antibody test (anti-MUSK) is available if regular MG antibodies are negative. Tensilon test can be useful if done by an experienced clinician if positive, again if negtive does not exclude a diagnosis of MG.
Thymus problems such as an overabundance of thymus tissue (thymic hyperplasia) or less commonly Thymus tumor can be associated with MG in a prooprtion of cases, although we are not sure why, and more so in younger patients. Therefore if a diagnosis is made of MG (even a test negtive but clinical diagnosis positive) then a CT scan of the neck should be done.