bulbar myasthenia gravis

My stepdad who is 68 years old and has been in good health had sudden onset of very nasal speech that was difficult to understand and severe difficulty swallowing accompanied by a severe global headache which is worse in the back and worse with coughing. A prior right eyelid droop (from a presumed Bell's Palsy 10 years ago) was worse and there was some droop of his right mouth and loss of the right nasolabial fold neither of which had been noted before. One week before the acute incident he noted that his hands felt hot when he put them in cold water.  The day before the incident he noted that ice water in his mouth left the sensation of having eaten hot chilis.  This dysthesia persists with anything cold in his mouth.  His neuro exam seems to show weakness in cranial nerves 7,9,10,&12 bilaterally.  Good sensory testing was not done but he does seem to have some numbness in his pharynx although his gag reflex is intact. His tongue and soft tissues in his pharynx are so big (swollen?) it is really hard to get a look at his throat.  He has gotten a brain CT without contrast, an MRI of the brain/brainstem without contrast, an MRI of the brain/brainstem with gadolinium, an MRA, a CT of the chest, an xray of the neck and sinuses, general bloodwork including thyroid all of which have been normal.   He had a modified barium swallow which he failed on the first trial and required suction to remove the barium from the valleculae.  His symptoms and signs have remained stable for 5 days.  He has been treated with Mestinon for 4 days with no improvement and has been started on IVIG for 1 day.  His acetylcholine receptor antibody test is pending.  

My questions are:
1.  Has anyone ever seen/heard of myasthenia presenting in this way, especially in light of the sensory changes?  Also I don't see any fatigability of the muscles.  His voice is the same nasally quality first thing in the morning as it is at bedtime or even after talking for several minutes.  His swallowing never works at all, it's not something that is better at different times.  The ice to the eyelid was maybe some improvement.

2.  If not myasthenia, what are the other possibilities?  I can't find anything that seems to fit.

3.  Are the radiology tests done sufficient to show a stroke or a tumor, say at the base of the skull?  His MRIs only took 15 minutes each, is that detailed enough to see all of the possibilities?  Could some possibilities require a special radiologist to read the studies?  He does not live in a big city and is not in a large institution hospital.  

Any insights would be greatly appreciated as this poor man has gone from excellent health to looking at needing a PEG and having to constantly suction his secretions in a matter of days.  Not knowing what is causing this makes matters so much worse.  Thank you.