Primary and secondary injury
A large percentage of the people killed by brain trauma do not die right away but rather days to weeks after the event; rather than improving after being hospitalized, some 40% of TBI patients deteriorate. Primary brain injury (the damage that occurs at the moment of trauma when tissues and blood vessels are stretched, compressed, and torn) is not adequate to explain this deterioration; rather, it is caused by secondary injury, a complex set of cellular processes and biochemical cascades that occur in the minutes to days following the trauma. These secondary processes can dramatically worsen the damage caused by primary injury and account for the greatest number of TBI deaths occurring in hospitals.Secondary injury events include damage to the blood–brain barrier, release of factors that cause inflammation, free radical overload, excessive release of the neurotransmitter glutamate (excitotoxicity), influx of calcium and sodium ions into neurons, and dysfunction of mitochondria. Injured axons in the brains white matter may separate from their cell bodies as a result of secondary injury, potentially killing those neurons. Other factors in secondary injury are changes in the blood flow to the brain; ischemia (insufficient blood flow); cerebral hypoxia (insufficient oxygen in the brain); cerebral edema (swelling of the brain); and raised intracranial pressure (the pressure within the skull). Intracranial pressure may rise due to swelling or a mass effect from a lesion, such as a hemorrhage. As a result, cerebral perfusion pressure (the pressure of blood flow in the brain) is reduced; ischemia results.
Early onset dementia is dementia in which symptoms first appear before the age of 65. The term favored until about 2000 was presenile dementia; young onset dementia is also used.Early onset dementia may be caused by degenerative or vascular disease, or it may be due to other causes, such as alcohol-related dementia and other inflammatory or infectious processes. Early-onset Alzheimers disease, vascular dementia and frontotemporal lobar degeneration are the most common forms of early onset dementia, with Alzheimers accounting for between 30 and 40%. Early onset dementia may also occur, less frequently, in the Lewy body dementias (dementia with Lewy bodies and Parkinsons disease dementia), multiple sclerosis, Huntingtons disease and other conditions. References
Further reading
Collins JD, Henley SM, Suárez-González A (July 2020). "A systematic review of the prevalence of depression, anxiety, and apathy in frontotemporal dementia, atypical and young-onset Alzheimers disease, and inherited dementia". Int Psychogeriatr (Review): 1–20. doi:10.1017/S1041610220001118. PMID 32684177. S2CID 220653830. Ducharme S, Dols A, Laforce R,  et al. (June 2020). "Recommendations to distinguish behavioural variant frontotemporal dementia from psychiatric disorders". Brain (Review). 143 (6): 1632–1650. doi:10.1093/brain/awaa018. PMC 7849953. PMID 32129844. Nwadiugwu M (September 2021). "Early-onset dementia: key issues using a relationship-centred care approach". Postgrad Med J (Review). 97 (1151): 598–604. doi:10.1136/postgradmedj-2020-138517. PMC 8408578. PMID 32883770. Roman de Mettelinge T, Calders P, Cambier D (2021). "The Effects of Aerobic Exercise in Patients with Early-Onset Dementia: A Scoping Review". Dement Geriatr Cogn Disord (Review). 50 (1): 9–16. doi:10.1159/000516231. PMID 33957623. S2CID 233983643.