Online searching has been unsuccessful for me in determining if dementia can start to show signs in late 30s, early 40s and if there's any definitive tests. Most articles just end with "talk to your doctor" and that's it. Are there tests out there that can help catch dementia early?

I'm asking because I had a very scary experience yesterday: Granted, I do not get my haircut at the same places frequently, I tend to just bounce around to whomever is available. But yesterday I got my haircut by someone new at a salon I've been to in the past. The stylist at the next chair over started to talking to me and addressing me by name in a very friendly manner. To me, it was the first time I've seen her and she was incredulous. She said, "I've cut your hair at least 3-4 times, maybe more, in the last 2 years". I'm a tall, big guy and she knew my name, so I don't have any reason to doubt her. But I just cannot remember her for the life of me. It scares me that someone is in my past like that and I have zero recollection of them. I mean, this isn't like, say, the person that takes your parking ticket in a booth. This is someone that has been in my "intimate" space on multiple occasions and I just cannot remember her. It has scared me.


Before answering your question, let’s first discuss some essential points:

What is dementia? As soon, somebody has “memory problems”, a diagnosis of “dementia” comes in mind. However, the definition of dementia is much more complex. Dementia is a clinical syndrome of cognitive decline that is sufficiently severe to interfere with social or occupational functioning. Cognitive decline affects different cognitive function such as memory but also language, executive and visuospatial functions. The most frequent cause of dementia is Alzheimer Disease (AD). Other common causes are vascular dementia (VaD), dementia with Lewy Bodies (DLB) and fronto-temporal dementia (FTD).

Your question

"determining if dementia can start to show signs in late 30s, early 40s”

Dementia is a condition that can affect younger individuals. Dementia related conditions onset before 65 years of age are defined as "Early-Onset Dementia" (EOD) or “Presenile Dementia”. While AD, VaD and DLB are frequent causes of EOD, Traumatic Brain Injury (TBI), Alcohol-associated Dementia (AAD), Huntington’s disease (HD), Parkinson’s disease Dementia (PDD), Mixed Dementia (MD) and Creutzfeldt-jakob disease (CJD) and Down’s syndrome are other frequent causes.

Epidemiological findings about the prevalence of EOD are scarce. According to the existing epidemiological studies, the prevalence of EOD ranges from 4.9 to 8 per 100.000 (35-39 years) and 11.9 to 17 per 100.000 (40-44 years) in your specified age group (late 30s, early 40s).

While some of the above mentioned diseases can appear “de novo” (without know risk factor), patients suffering from EOD often have a positive family history for dementia related conditions.

Your question

"if there's any definitive tests to diagnose dementia”

As already mentioned, dementia is a clinical syndrome which is largely heterogenous in its clinical presentation, aetiology and underlying pathophysiology. As such, each type of dementia related conditions is defined by specific criteria which are based on clinical examination, neuropsychological assessments and neuroimaging studies.

The diagnosis of dementia is associated with important consequences for the patient. As such, in many countries, assessment of dementia is carried out by specialised clinics called “Memory Clinic”, where the patient is seen by a team of different specialists such as neurologist, psychiatrist and neuropsychologist. The patient undergoes a series of clinical (neurological and gait examination) and neuropsychological tests as well as a brain MRI (if no contra-indications) and/or PET Scan (depending on the presentation). The diagnosis of dementia is then discussed in a team composed of all the specialists.

In the last decades, the use of biomarkers (molecules which are specific “markers” of a disease) in the cerebrospinal fluid for example are investigated as potential “markers” to diagnose a specific dementia related conditions. This has however still to be confirmed in the next decades.

Concerning your experience:

It is of course difficult to draw a conclusion on what happened to you but I hope that the above points brought some clarifications. Additionally, bear in mind that memory is a complex cognitive function that relies on elaborated neuronal cortical networks and is influenced by other cognitive functions such as for example attention. A lack of attention or concentration can impact on the process of memory. This can for example happen in stress situation or emotional situation. Finally, some drugs may also interfere with the process of memory. As such, there are other possible factors that could explain some “blackouts”, that probably many individuals experience without necessarily suffering from dementia. If, in the previous mentionned points, you see a so called "red flag" (problems in other cognitive areas, impact on social or occupational functioning, risk factors such as positive family history) which concerns your own history, you may wish to consider seeing your family doctor.


  • Dickerson, B. and Atri, A. at al. Dementia: Comprehensive Principles and Practice. Oxford University Press. 2014. (an excellent reference book for dementia)
  • Plassman, B.L. et al. “Prevalence of Dementia in the United States: The Aging, Demographics, and Memory Study.” Neuroepidemiology 29.1-2 (2007): 125–132
  • Vieira RT et al. Epidemiology of early-onset dementia: a review of the literature. Clin Pract Epidemiol Ment Health. 2013 Jun 14;9:88-95.
  • Vieira, Renata Teles et al. “Epidemiology of Early-Onset Dementia: A Review of the Literature.” Clinical Practice and Epidemiology in Mental Health : CP & EMH 9 (2013): 88–95.
  • Gabrieli JD et al. Cognitive neuroscience of human memory. Annual Review of Psychology. Vol. 49: 87-115

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