1. (a) General. Except as provided in § 3.300(c), disability which is proximately due to or the result of a service-connected disease or injury shall be service connected. When service connection is thus established for a secondary condition, the secondary condition shall be considered a part of the original condition.

2. (b) Aggravation of nonservice-connected disabilities. Any increase in severity of a nonservice-connected disease or injury that is proximately due to or the result of a service-connected disease or injury, and not due to the natural progress of the nonservice-connected disease, will be service connected. However, VA will not concede that a nonservice-connected disease or injury was aggravated by a service-connected disease or injury unless the baseline level of severity of the nonservice-connected disease or injury is established by medical evidence created before the onset of aggravation or by the earliest medical evidence created at any time between the onset of aggravation and the receipt of medical evidence establishing the current level of severity of the nonservice-connected disease or injury. The rating activity will determine the baseline and current levels of severity under the Schedule for Rating Disabilities (38 CFR part 4) and determine the extent of aggravation by deducting the baseline level of severity, as well as any increase in severity due to the natural progress of the disease, from the current level.

   (Authority: 38 U.S.C. 1110 and 1131)

3. (c) Cardiovascular disease. Ischemic heart disease or other cardiovascular disease developing in a veteran who has a service-connected amputation of one lower extremity at or above the knee or service-connected amputations of both lower extremities at or above the ankles, shall be held to be the proximate result of the service-connected amputation or amputations.

4. (d) Traumatic brain injury.

   1. (1) In a veteran who has a service-connected traumatic brain injury, the following shall be held to be the proximate result of the service-connected traumatic brain injury (TBI), in the absence of clear evidence to the contrary:

      1. (i) Parkinsonism, including Parkinson's disease, following moderate or severe TBI;
      2. (ii) Unprovoked seizures following moderate or severe TBI;
      3. (iii) Dementias of the following types: presenile dementia of the Alzheimer type, frontotemporal dementia, and dementia with Lewy bodies, if manifest within 15 years following moderate or severe TBI;
      4. (iv) Depression if manifest within 3 years of moderate or severe TBI, or within 12 months of mild TBI; or
      5. (v) Diseases of hormone deficiency that result from hypothalamo-pituitary changes if manifest within 12 months of moderate or severe TBI.
   2. (2) Neither the severity levels nor the time limits in paragraph (d)(1) of this section preclude a finding of service connection for conditions shown by evidence to be proximately due to service-connected TBI. If a claim does not meet the requirements of paragraph (d)(1) with respect to the time of manifestation or the severity of the TBI, or both, VA will develop and decide the claim under generally applicable principles of service connection without regard to paragraph (d)(1).

   3. (3)

      1. (i) For purposes of this section VA will use the following table for determining the severity of a TBI:

         Mild	Moderate	Severe
         Normal structural imaging	Normal or abnormal structural imaging	Normal or abnormal structural imaging.
         LOC = 0-30 min	LOC > 30 min and < 24 hours	LOC > 24 hrs.
         AOC = a moment up to 24 hrs	AOC > 24 hours. Severity based on other criteria.
         PTA = 0-1 day	PTA > 1 and < 7 days	PTA > 7 days.
         GCS = 13-15	GCS = 9-12	GCS = 3-8.

      2. (ii) The determination of the severity level under this paragraph is based on the TBI symptoms at the time of injury or shortly thereafter, rather than the current level of functioning. VA will not require that the TBI meet all the criteria listed under a certain severity level in order to classify the TBI at that severity level. If a TBI meets the criteria in more than one category of severity, then VA will rank the TBI at the highest level in which a criterion is met, except where the qualifying criterion is the same at both levels.

         (Authority: 38 U.S.C. 501, 1110 and 1131)

Note: The factors considered are: Structural imaging of the brain. LOC—Loss of consciousness. AOC—Alteration of consciousness/mental state. PTA—Post-traumatic amnesia. GCS—Glasgow Coma Scale. (For purposes of injury stratification, the Glasgow Coma Scale is measured at or after 24 hours.)

[44 FR 50340, Aug. 28, 1979, as amended at 66 FR 18198, Apr. 6, 2001; 71 FR 52747, Sept. 7, 2006; 78 FR 76208, Dec. 17, 2013]