A history of traumatic brain injury (TBI) is recognised as a major risk factor for neurodegenerative disease (NDD), with around 3-15% of dementia in the community thought to be a consequence of prior TBI exposure. In line with this, former contact sports with histories of exposure to repetitive TBI and head impacts have high risk of neurodegenerative disease when compared to general population datasets. However, reasons why TBI might increase risk of NDD remain uncertain. Studies of TBI outcomes in the general population report that wider general health is also impacted, including higher rates of cardiovascular disease and mental health disorder in TBI survivors, which are, in themselves, recognised risk factors for NDD. However, in contrast to these general population data, observations in former athletes report better wider health, including lower cardiovascular disease and mental health disorder.
The relationship between TBI and risk of NDD is complex and likely to reflect an interaction between the direct consequences of the injury to the brain and the influence of TBI on wider systemic health, in turn, indirectly impacting on brain health. To better understand the relationship between TBI and late NDD risk there is a need to gain a more holistic insight into lifelong health outcomes following TBI exposure and their potential interactions in modifying risk.
We will contrast baseline TBI vs. n=3 controls matched for age, sex, deprivation and years of up-to-standard (UTS) data, in terms of subsequent mortality and mental health outcomes. Participants will require at least 7 years up to UTS: one for exposure, one for covariate ascertainment, and five years for condition incidence (where a GOLD UTS date is assigned to a CPRD practice and the data recorded by the practice are of an acceptable research standard). Conditions will be based on a priori Read/SNOMED code lists.
• History of traumatic brain injury
• Primary and secondary causes of death, specifically deaths from the most common causes in the community (diseases of the circulatory system; diseases of the respiratory system; cancer; neurodegenerative disease) or where cause of death is recorded as suicide.
• Diagnosis of mental health disorder, specifically diagnosis of the most common mental health disorders in the community (anxiety and stress disorder; depression; alcohol use disorder; drug use disorder; bipolar and affective mood disorder).
• Diagnosis of neurodegenerative disease, specifically diagnoses of common dementias and neurodegenerative diseases (all neurodegenerative diseases; dementia not otherwise specified; Alzheimer’s disease; non-Alzheimer’s dementias; motor neuron disease; and Parkinson’s disease)
• Prescribing of medications for dementia, specifically prescribing of drugs listed under Section 4.11 of the British National Formulary.