The Singapore Law Gazette

An Introduction to Dementia for Lawyers Dealing with Cases Involving Mental Capacity

Introduction

The ageing population in Singapore means that we are likely to see an ever-increasing number of cases that involve a loss of mental capacity, and lawyers may encounter such cases in many different ways, for example, in Mental Capacity Act 2008 (“MCA”) applications and in disputes over testamentary capacity.

This paper therefore aims to provide a brief introduction to dementia as it is one of the most common medical conditions causing loss of mental capacity, and it is commonly encountered in MCA applications for the appointment of deputies as well as in disputes relating to the validity of a Lasting Power of Attorney (“LPA”) and also testamentary capacity.

Although lawyers would normally rely on a medical expert in such cases, there are also many circumstances where lawyers may interact with the patients in question and having some knowledge about these conditions can be useful. For example, a lawyer may act as a certificate issuer for an LPA or may need to form a view about a client’s mental capacity or a testator’s testamentary capacity or a professional deputy may need to consider if the subject of the deputyship order (“P”) has mental capacity to make a particular decision. In addition, lawyers would need to critically evaluate the medical expert’s report, for example, to decide whether it is sufficient to convince the court that the patient in question lacks mental capacity in an application for appointment of a deputy under the MCA.

What Is Dementia?

Dementia is “a syndrome that can be caused by a number of diseases which over time destroy nerve cells and damage the brain, typically leading to deterioration in cognitive function (i.e. the ability to process thought) beyond what might be expected from the usual consequences of biological ageing”¹International Classification of Diseases, 11^th revision.

A recent study estimates that 8.8% of people aged 60 and above have dementia and that about one in two people aged 85 and above have dementia²Teo J “Prevalence of dementia in Singapore falls to 1 in 11 among older adults: IMH study”, The Straits Times 28^th August 2024. Of particular relevance to lawyers dealing with elderly clients is the finding that about 51.5% of dementia cases in Singapore remain undiagnosed³Subramaniam M et al, “Prevalence of dementia in Singapore: Changes across a decade”, Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association (2025) 21(2): e14485. As such, there is a very real possibility that a client who exhibits signs of cognitive decline may actually have undiagnosed dementia. Therefore, lawyers dealing with such clients must be mindful of this possibility when taking instructions and assessing capacity.

Although it is often said that dementia is associated with a decline in memory, and this is certainly true of dementia due to Alzheimer’s Disease, other forms of cognitive decline (for example, in executive function, social cognition, attention or language) may be more prominent in some patients.

Dementia or Major Neurocognitive Disorder?

The term “dementia” has been used in modern medicine since at least the late 18^th century⁴Boller F and Forbes MM, “History of dementia and dementia in history: An overview”, Journal of the Neurological Sciences (1998) 158: 125-133, and it is currently still widely used. In particular, it is used in the World Health Organization’s International Classification of Diseases 11^th Revision (or ICD-11).

However, the term “dementia” has been replaced by “major neurocognitive disorder” in the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders 5^th Edition (or DSM-5) although it is also made clear that the term “dementia” can continue to be used. Specifically, DSM-5 provides that dementia “is subsumed under the newly named entity major neurocognitive disorder”⁵Diagnostic and Statistical Manual of Mental Disorders, 5^th edition, at p591 and that major neurocognitive disorder “corresponds to the condition referred to in DSM-IV as dementia”⁶Ibid, at p607 but also that “[t]he term dementia … may be used in settings where physicians and patients are accustomed to this term”⁷Ibid, at p591.

As such, lawyers may encounter both terms in the reports of medical experts, and both terms are perfectly acceptable to describe the conditions of the patients in question. However, it is important to note that the definition of “major neurocognitive disorder” is actually broader than that of “dementia” and certain conditions (for example, amnestic disorder) which would not fall within the definition of “dementia” now fall within the definition of “major neurocognitive disorder”⁸Ibid.

Causes of Dementia

Dementia can be due to a number of different diseases or causes. The more common forms of dementia are dementia due to Alzheimer’s Disease, vascular dementia, dementia with Lewy bodies and frontotemporal dementia.

Dementia due to Alzheimer’s Disease is the most common form of dementia, and it accounts for about 60% to 80% of dementia cases⁹Centers for Disease Control and Prevention, “About Dementia” (17 August 2024) <https://www.cdc.gov/alzheimers-dementia/about/index.html>.. Alzheimer’s Disease is a neurodegenerative disease involving damage to brain cells over time, and it is characterised by deposits of abnormal proteins called amyloid plaques in the brain¹⁰Under the 2024 Alzheimer’s Association revised criteria, Alzheimer’s Disease is now defined biologically by abnormalities on core biomarkers (Jack CR et al, “Revised criteria for diagnosis and staging of Alzheimer’s disease: Alzheimer’s Association Workgroup”, Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association (2024) 20(8): 5143-5169), but it is important to note that a positive biomarker only establishes the presence of disease but not incapacity.. Often, the first symptom reported is memory impairment, and patients usually show a slow but steady decline in cognitive functioning.

The next most common form of dementia is vascular dementia, and this accounts for about 5% to 10% of dementia cases¹¹Ibid, at xi.. This form of dementia is caused by strokes or other conditions which affect blood flow to the brain. As a result, the onset of dementia occurs after the patient suffers from such a condition, and, over time, the condition progresses and the patient’s symptoms get worse.

As such, one feature that helps to distinguish between dementia due to Alzheimer’s Disease and vascular dementia is the onset of symptoms. In Alzheimer’s Disease, the decline is slow and gradual but, in vascular dementia, the onset is typically more sudden and abrupt although this may not always be the case for patients with a type of vascular dementia called subcortical vascular dementia¹²Karantzoulis S and Galvin JE, “Distinguishing Alzheimer’s disease from other major forms of dementia”, Expert Review of Neurotherapeutics (2011) 11(11): 1579–1591. This fact can be important to lawyers as a patient who was previously well may, after suffering a stroke, have a relatively fast and sudden decline in cognitive ability.

Dementia with Lewy bodies is the third most common form of dementia¹³Yang SK, et al, “Incidence and comorbidity of dementia with Lewy Bodies: A population-based cohort study”, Behavioural Neurology (2018) May 29 (although some sources classify it as the second most common form of dementia and it is thought to be under-diagnosed due to its clinical features overlapping with other conditions), and it accounts for about 3% to 7% of dementia cases¹⁴Hogan DB, et al, “The Prevalence and Incidence of Dementia with Lewy Bodies: a Systematic Review”, Canadian Journal of Neurological Sciences (2016) 43(S1): S83-S95. This form of dementia is caused by abnormal deposits of a protein called “Lewy bodies” in the brain, and these abnormal proteins interfere with the normal functioning of the brain. Although Alzheimer’s Disease and Lewy Body Dementia are both associated with the deposit of abnormal proteins in the brain, the protein deposits are different and their symptoms are also different. In particular, patients with Lewy Body Dementia tend to suffer from hallucinations and movement disorders while such symptoms are uncommon in patients with Alzheimer’s Disease¹⁵Wiese LJ, Lingler J and Linadauer A, “Alzheimer’s disease and Lewy body dementia: Discerning the differences”, American Nurse Journal (2021) 16(1): 10-17.

Frontotemporal dementia is an umbrella term that describes a group of disorders that affect the frontal and temporal lobes of the brain. In this form of dementia, patients typically exhibit problems with behaviour and language. Also, the age of onset of frontotemporal dementia tends to be lower than in other forms of dementia. This fact can be important to lawyers as younger people will, more often than older people, be involved in legal matters such as running businesses and entering into contracts, and, as such, the legal and financial fallout from an undetected decline in cognitive ability can be very serious.

Lastly, mixed dementia describes the condition when a patient suffers from more than one type of dementia. The most common form of mixed dementia is a combination of Alzheimer’s Disease and vascular dementia.

Severity

The severity of dementia can be classified into three stages (mild, moderate, and severe) based on the degree of the patient’s “neurocognitive and functional impairment, and capacity for independence in activities of daily living”¹⁶International Classification of Diseases, 11^th revision.

In patients with mild dementia, the clinical signs may be subtle enough that the individual appears unimpaired to casual acquaintances. However, there will typically be some impairment of judgement and problem-solving and also difficulty with complex decisions and handling finances.

In patients with moderate dementia, the cognitive impairment becomes obvious and such patients will have difficulties with basic activities of daily living, for example, dressing and personal hygiene. Also, there will typically be significant memory loss and impairment of judgement and problem-solving. In addition, communication and socialising become increasingly difficult and such patients may also behave inappropriately, for example, in a disinhibited or aggressive manner.

In patients with severe dementia, the memory impairment will often be severe but this may vary depending on the type of dementia. Such patients are often completely unable to exercise judgement or engage in problem-solving, and they would typically have difficulty in understanding what is happening. As such, they would normally be fully dependent on others for even basic personal care.

It is, however, important to bear in mind that a patient with severe dementia is not automatically incapable of making all decisions. Because the test for capacity is both decision-specific and time-specific, the clinical severity of dementia assists in the assessment of a patient but is not a substitute for the functional inquiry into the particular decision in question.

Screening Tests

When reviewing medical reports on patients with dementia, there will often be a mention of tests such as the MMSE, MoCA and AMT.

“MMSE” stands for “Mini-Mental State Examination”. This test was first published by Folstein and colleagues in 1975 and is now the most widely used clinical test for cognitive assessment¹⁷Gallegos M et al, “45 Years of the mini-mental state examination (MMSE): A perspective from Ibero-America”, Dementia & Neuropsychologia (2022) 16(4): 384–387. It tests various areas of cognitive ability, for example, orientation to time and place as well as memory and comprehension.

“MoCA” stands for “Montreal Cognitive Assessment”. This test was developed as a screening tool to detect mild cognitive impairment and it assesses “multiple cognitive domains including attention, concentration, executive functions, memory, language, visuospatial skills, abstraction, calculation and orientation”¹⁸Julayamont P et al, “Montreal Cognitive Assessment (MoCA): Concept and clinical review”. In: Larner AJ (ed), Cognitive screening instruments: A practical approach (2013, Springer-Verlag Publishing), pp111–151. It has been found to be more sensitive than the MMSE in relation to detection of mild cognitive impairment.

It is, however, important for lawyers to bear in mind that scores of the MMSE and MoCA are sensitive to age, education and language, and this is a particularly important consideration in a multi-lingual and multi-ethnic population such as that in Singapore.

“AMT” stands for “Abbreviated Mental Test”. This is a 10-question test that was designed to quickly assess patients for cognitive impairment¹⁹Peters KA, “The Abbreviated Mental Test Score; Is there a need for a contemporaneous update?”, Geriatric Orthopaedic Surgery & Rehabilitation (2021) 12. However, while this test is short and easy to administer, researchers have widely different views about the reliability and limitations of this test.

However, it is important to note that these tests are used to give doctors a sense of the patient’s cognitive ability and they cannot be used to definitively diagnose dementia in the sense that if a patient scores below any particular number, the patient definitely has dementia.

Assessing a Medical Report

When assessing the report of a medical expert, it is important to bear in mind what the Court of Appeal held in Re BKR²⁰[2015] SGCA 26.

In this case, the Court of Appeal held as follows in relation to “the proper limits of the expert evidence”²¹Re BKR [2015] SGCA 26, at [133]:

… the test for capacity in s 4(1) of the MCA may be thought of as having a functional and a clinical component – the functional aspect is that P must be unable to make a decision, and the clinical aspect is that this inability must be caused by a mental impairment. It is not difficult to see that we require the assistance of expert evidence when addressing the clinical component of the test: we need medical professionals to tell us whether P has a mental impairment based on the observable symptoms and any other diagnostic tools available, and if so, what that impairment is, and what effect it has on P’s cognitive abilities. But as to the functional component, it is in our judgment a question for us to grapple with leaving perhaps a limited scope for the involvement of the medical ²²Ibid, at [134] experts.

Therefore, while medical experts commonly give an opinion in their reports about whether they think that the patient has or does not have mental capacity, what is more important is that the medical reports set out the patient’s diagnosis (and, of course, the clinical history, clinical examination findings and investigation reports that led to this diagnosis). In addition, a detailed record of what was said by the patient and what was found during clinical examination is critical in assisting the court to come to a conclusion about the functional component of the test, i.e. whether P is able or unable to make the decision in question.

Conclusion

In conclusion, in an era defined by Singapore’s rapidly shifting demographics, mental capacity issues can no longer be viewed as peripheral legal concerns. Recent cases²³For instance, see: XKG v XKF [2026] 3 SLR 1450 CBB v Wong Tien Leong William [2026] SGHC 53 also illustrate the professional and liability risks facing lawyers in this area. As such, an understanding of conditions like dementia is not merely useful but actually indispensable given how any client or potential client could, unbeknownst to the lawyer, be experiencing cognitive decline and mental capacity issues.

 

The author would like to thank Adj A/Prof Tor Phern Chern, Senior Consultant at the Department of Psychological Medicine, National University Hospital, for his helpful comments and advice.