I contacted Dr Drew to file a secondary claim to my PTSD and went from 70% to 90% total disability in less than a month! Dr Drew wrote a very professional Nexus letter that showed evidence of "more likely than not" that my Sleep Apnea was caused by or aggravated by my PTSD based on medical research. To get any response from the VA in less than a month is unheard of and I believe the Nexus letter sealed the deal for me. I would highly recommend using Dr Drew for your Nexus Letter, Veteran to Veteran. Don't file your claim without a Nexus letter even if you have other evidence.