I am sorry; I don't even know what the USMLE exam is. I am a 44-year old woman with a severe learning disability. It is complicated, but it involves executive functioning as well as visual processing.
I am studying for the LSAT (Law School Admissions Test). I have applied for special accommodations and the committee has treated me like dirt. I've been waiting months for an answer and have missed 2 test administrations simply because they dragged their feet. I wrote a 5 page letter to the president of the company that administers the test. I gave him all of the details and then told him that if they do not grant me accommodations for the next exam (Feb) that I plan to file a complaint with the Department of Justice. And believe me; I will.
I recommend that you, "dot every i and cross every t" when it comes to documenting your disability. Also, ask for more than you really need. For example, I asked for triple time on the writing sample. I think I could get by with double time, but I asked for it anyway. Chances are that they are going to come down from what I asked for, so I may as well start high.
Make sure that your examiner does a decent job of advocating for you in your request for accommodations . They really have to sell it.
If you do get turned down, raise hell! contact the Dept of Justice. Call or write to them and ask them to send you a compliant form (for disability rights)
U.S. Department of Justice
950 Pennsylvania Avenue, NW
Civil Rights Division
Disability Rights-NY AVE
Washington, D.C. 20530
Good luck on the exam! Write back if you have questions.