This site complies with the HONcode standard for trustworthy health information:
verify here.

Hints for Your FAA Medical Examination and Keeping Your Pilot Medical Certificate

11.  Be prepared to send further information to the FAA upon request

Occasionally, pilots will receive a letter from the FAA after they have been issued a medical certificate by their AME. The letter states that the FAA is unable to determine their eligibility for an airman medical certificate based on incomplete information regarding some medical condition. The FAA specifically requests information and/or further studies to be submitted prior to an eligibility determination. Usually, there is a 30-day suspense from the date of the letter on this submission requirement. Attempt to comply with this time line and submit all requested information. If it is impossible to complete this requirement prior to the 30-day extension, a call to the FAA requesting a 30-day extension is all that is needed. The pilot may continue to operate an aircraft with a current medical certificate issued by the AME pending a final determination from the FAA. Denial letters from the FAA come via certified mail and specifically request a return of the medical certificate.