38 C.F.R. § 4.42

The importance of complete medical examination of injury cases at the time of first medical examination by the Department of Veterans Affairs cannot be overemphasized. When possible, this should include complete neurological and psychiatric examination, and other special examinations indicated by the physical condition, in addition to the required general and orthopedic or surgical examinations. When complete examinations are not conducted covering all systems of the body affected by disease or injury, it is impossible to visualize the nature and extent of the service connected disability. Incomplete examination is a common cause of incorrect diagnosis, especially in the neurological and psychiatric fields, and frequently leaves the Department of Veterans Affairs in doubt as to the presence or absence of disabling conditions at the time of the examination.