What Causes Muscle Twitching Of The Neck?
The only remotely similar thing
I read your question carefully and I understand your concern.
Judging from your description that twitching seems like muscle fasciculations, involuntary discharge and contraction of a group of muscle fibers.
Fasciculations can have many different causes. Often on this site I get questions from people who after reading online fear degenerative neuromuscular diseases like ALS. Let me reassure you though, in the absence of other symptoms that is not the cause, not without some muscle weakness. Also the age alone would make it extremely unlikely as such neuromuscular conditions appear usually after the age of 40.
Most common cause of such fasciculations in a young man would be what is called benign fasciculations syndrome. As the name suggests it is completely benign. The cause is not well known, stress and anxiety are possible contributors.
However some hormonal or metabolic causes should be considered. Altered thyroid function is a possible cause in your sons case. Other metabolic causes would include electrolyte alterations, in particular in the levels of calcium and magnesium, so an electrolyte panel is recommended in addition to repeat thyroid function tests.
I remain at your disposal for other questions.