38 CFR § 4.14 - Avoidance of pyramiding.
The evaluation of the same disability under various diagnoses is to be avoided. Disability from injuries to the muscles, nerves, and joints of an extremity may overlap to a great extent, so that special rules are included in the appropriate bodily system for their evaluation. Dyspnea, tachycardia, nervousness, fatigability, etc., may result from many causes; some may be service connected, others, not. Both the use of manifestations not resulting from service-connected disease or injury in establishing the service-connected evaluation, and the evaluation of the same manifestation under different diagnoses are to be avoided.