Testimonials from patients of Dr. Cullen. My personal Experience with Dr Collin Cullen. from Gundu in MD March 12, 2020 for Collin D. Cullen, MD. In my half a century of stay in the USA, Dr. Collin Cullen is just the second internist, that I am seeing for my general preventive healthcare. I am a long-term diabetic (>20years), and I do need ....