A related discussion,
cyst T.B. was started.
I would think an attempt should be made to biopsy the cysts, to see if the pathogen can be diagnosed. Has a dermatologist looked at them? Has he had a complete physical, with CBC blood tests, chest x-ray, etc? Infectious disease doctor consult would be good.
It would seem to be a bit of a leap to presume a positive skin test showing exposure to TB, to be the source of the cysts. Once put on the multiple antibiotic TB treatment, he may develop side effects that confound the true diagnosis.
I would think a high rated teaching hospital could diagnose what it is. See US News & World Report ranking of hospitals:
http://www.usnews.com/usnews/nycu/health/hosptl/tophosp.htm
America's Best Hospitals 2003
Mass. General in Boston and NY Presbyterian Hospital are high ranked in your region.
If your son is young enough and healthy enough to undergo the treatment to eradicate the TB in his system - encourage him to go for it! If not, he will carry the TB in his system for the REST of his life. At anytime if his immune system becomes seriously compromised, if he gets repeated viral/bacterial infections, pneumonia, diabetes, HIV, etc. etc. etc.....he will be especially vulnerable. At ANYTIME he could develop active TB and present a risk to those closest to him. It is also very expensive to treat. At this time, his treatment would like be covered by the Peace Corps.
Trust me, wondering every time you are "symptomatic" is a really stressful way to live. Everytime your son gets a bronchial infection or any upper respiratory illness with night sweats and a cough that won't quit you will all wonder.
The cysts that you have described are an unusual presentation for tuberculosis (TB). I would have your son see an infectious disease specialist in your area for further advice.