Yes, you can. The weight given to such a letter may or may not be as great as the NARSUM. It really depends on the underlying facts. I would also say, a "one off" letter written for forensic type purposes would likely not carry as much weight as coming from a physicican/specialist who has been treating you over time. To a degree, credentials do matter. A board certified doctor's opinion will normally carry more weight than a doctor with less experience/credentials (whose opinion, in turn, will normally carry more weight than that of a nurse or a PA).I was curious if things don't go well during my MEB/PEB I could get a letter from a doctor that who I would pay to write a report like a IMO/IME, nexus letter to help me out if I don't agree with the Army physicians on my Narsum?