Myasthenia Gravis ?

I’m a 56 year old male.  I’ve had the following symptoms for almost 10 years:  

1)  Difficulty swallowing anything but liquids. I’m often unable to initiate a swallow or to move food past my tongue into my throat under my control.  Chewing or moving a bolus around to initiate a swallow causes jaw, throat, and tongue fatigue, often a bruised feeling below and behind my Adam’s apple.  Cold liquids are better than hot liquids.  The condition is best in the morning after sleep (cereal and toast for breakfast), however it worsens throughout the day (only soup at lunch).  I sometimes cannot eat at all at dinner time.  I cannot swallow anything that must be chewed (no meat, pasta, etc.).  About once a week I aspirate (“wrong pipe”) water or other liquid.  I find it very difficult to swallow large pills

2)  My speech is often slurred and unintelligible when fatigued, producing a gravelly, nasal sound.  At these times it requires a lot of airflow to make a sound. As with swallowing, my speech is generally better when rested, especially in the morning.

3)  I often experience apnea when lying on my back or reclining.  I wake up suddenly gasping.

4)  My facial expression is seen as stern or somber by others.  I do not smile well.

5)  Muscles other than facial and throat are not as affected, however I walk slower than I used to.  I notice fatigue in my thigh muscles after walking long distance or exercise.  I have poor small-motor skills in my hands, frequently dropping bottle caps, etc.  Hot weather exacerbates my symptoms.

My neurologist suspected Myasthenia Gravis.  My AchR Antibodies and MuSK antibodies tests were negative.  A Single Fiber EMG showed myopathy in my facial muscles.  A Nerve Conduction - Repetitive Nerve Stimulation showed some jitter, but not extreme.  A barium swallow confirmed my dysphagia. A Gastric Emptying test showed an abnormal emptying rate.  A deltoid muscle biopsy showed nothing extraordinary.  I’ve had genetic testing for several dystrophies, but those tests were negative.

Can one have MG and have negative AchR and MuSK tests?  Can a diagnosis be made by clinical observation alone?  What else might cause my symptoms?