Neurocognitive Disorder / Cognitive Impairment Secondary to Traumatic Brain Injury (TBI)

Yes. Under 38 CFR § 3.310(a), any disability proximately caused or chronically worsened by a service-connected condition is itself service-connected. Neurocognitive Disorder / Cognitive Impairment is a documented secondary pairing for Traumatic Brain Injury (TBI) with strong medical evidence. A nexus letter from a qualified physician linking the two conditions is the most reliable way to establish this connection.

The gold standard is a private nexus opinion stating — to at least a 50% probability ("at least as likely as not") — that the secondary condition was caused or aggravated by the primary service-connected condition. Peer-reviewed medical literature supporting the physiological mechanism strengthens the nexus. Treatment records documenting the onset or worsening of the secondary condition in temporal relation to the primary are supporting evidence.

The VA rates Neurocognitive Disorder / Cognitive Impairment separately under its own 38 CFR Part 4 diagnostic code, then combines it with Traumatic Brain Injury (TBI) and all other service-connected ratings using the combined ratings formula under § 4.25. The formula applies the whole-person concept: a 50% combined existing rating plus a new 30% rating yields 65% (rounded to 70%), not 80%.

38 CFR § 3.310(a) states: "Disability which is proximately due to or the result of a service-connected disease or injury shall be service connected." The aggravation variant under § 3.310(b) applies where the primary condition permanently worsens a pre-existing disability beyond its natural progression. Both standards require a showing of nexus — a medical or scientific link between the primary condition and the secondary.

The medical evidence supporting Neurocognitive Disorder / Cognitive Impairment as secondary to Traumatic Brain Injury (TBI) is rated strong. TBI causes diffuse axonal injury (DAI) that disrupts white matter tracts connecting the prefrontal cortex, hippocampus, and thalamus — regions critical for executive function, working memory, and processing speed. Neuroinflammatory cascades triggered by the initial mechanical insult persist for months to years through microglial activation, producing ongoing neuronal loss and synaptic dysfunction. Studies using diffusion tensor imaging demonstrate that even mild TBI produces measurable reductions in fractional anisotropy in the corpus callosum and corona radiata that correlate with neuropsychological test performance deficits.

The VA will not solicit nexus evidence on your behalf for secondary claims. In practice, a written nexus opinion from a private physician or independent medical examiner is essential — the VA's Compensation & Pension (C&P) examiner is not required to produce a favorable nexus opinion, and the VA has discretion to weigh competing opinions. Submitting a private nexus letter at the time of filing is the most reliable strategy.