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Lewy Body Dementia

and Intellectual Disability

Lewy Body Dementia and Intellectual Disability

According to the Lewy Body Dementia Association, Lewy body dementia (LBD) is the 2nd most common type of progressive dementia after Alzheimer’s disease. This condition affects more than a million people in the United States. Because LBD symptoms may closely resemble other, more commonly known disorders like Alzheimer’s disease, it is widely under-diagnosed.

LBD is an umbrella term for two related diagnoses:

  • A form, diagnosed as dementia with Lewy bodies (DLB), is where adults will develop dementia and other symptoms (such as changes in affect and behavior) early in the course of the disease, and frequently experience changes in movement, like a tremor or muscle rigidity (parkinsonism)

  • A form where adults will present first with changes in movement, leading to a Parkinson’s disease diagnosis, then develop dementia years later -- is termed Parkinson’s disease dementia (PDD).

Adults with LBD frequently present with changes in affect and behavior, a notable loss of smell, and with psychotic symptoms (including hallucinations and delusions)

Studies of adults with intellectual disability show that the prevalence of LBD is similar to that of adults in the general population (the second most prevalent cause of dementia, after Alzheimer's disease). It has also been diagnosed in adults with Down syndrome but to a significantly lessor degree than Alzheimer's disease as a primary cause of dementia.

Recent work is also examining a shift in conceptualizing this form of dementia as a 'neuronal α-synuclein disease'. This would base the diagnosis and definition of the disorder on the underlying biology rather than on the description of the syndrome. A biological definition
of disease would provide diagnostic clarity by uniting under a common mechanistic umbrella patients with neuronal α-synucleinopathy who might present syndromically as Parkinson’s disease, Parkinson’s disease dementia, idiopathic rapid eye movement-sleep behavior disorder, or dementia with Lewy bodies.


[Source: Jack, C.R., Criteria for a biological definition of neuronal α-synuclein disease—a major conceptual step forward.  Lancet Neurol. 2024 Feb;23(2):178-190.  doi: 10.1016/S1474-4422(23)00405-2.]

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Information on Lewy Body Dementia

Looking for resources on Lewy Body Dementia?

We have drawn upon materials available from the Lewy Body Dementia Association for some general information  (click on item title to access item)
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Diagnosing LBD

No single test can diagnose Lewy body dementia.

Doctors typically diagnose Lewy body dementia by eliminating other diseases and conditions that cause similar symptoms.

Common assessments can include a neurological exam to assess:

  • The way a person walks (referred to as a ‘gait analysis’)

  • Posture

  • How rigid or stiff the person’s body is

Other measures to assist in a diagnosis include:

  • Obtaining a detailed medical history

  • Brain imaging (e.g. MRI)

  • Physical and neuropsychological testing


Lewy Body Dementia Symptoms

  • Unpredictable changes in concentration, alertness, or attention

  • Parkinson’s-like symptoms,including slowness of movement, rigidity or stiffness, shuffling gait, tremors, and balance problems

  • Behavioral changes, including hallucinations, delusions, or changes in mood

    • Hallucinations involve seeing or hearing things that are not really present and can also occur in senses like touch and smell

    • Delusions (false beliefs) and paranoia (unwarranted suspicions), sometimes alone or in response to threatening hallucinations

    • Changes in mood, including depression, anxiety, and apathy

  • Sleep disorders including REM sleep behavior disorder (RBD), excessive daytime sleepiness, temporary loss of consciousness with difficulties wakening, insomnia, and restless leg syndrome

  • Autonomic symptoms, including problems with temperature and blood pressure regulation can occur, as well as constipation, urinary incontinence, and sexual dysfunction

Comprehensive LBD Symptom Checklist

The LBDA's checklist designed to help physicians and their patients identify key LBD symptoms and which can be used at or provided to a physician during an office visit.

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To reach the Lewy Body Dementia Association

Click on logo

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Lewy Body Dementia: Information for Patients, Families, and Professionals

This NINDS publication is meant to help people with Lewy body dementia, their families, and professionals learn about this disease and resources for coping. It explains what is known about the different types of Lewy body dementia and how they are diagnosed. Information about the treatment and management of this disease, with practical advice for both people with Lewy body dementia and their caregivers is provided.

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Information on Intellectual Disability and Lewy Body Dementia

A listing of some published work on Lewy Body dementia in adults with intellectual disability is provided below

A pathological study of the association between Lewy body disease and Alzheimer's disease.

The possibility of an association between Parkinson's disease and Alzheimer's disease has been examined by studying the age-specific prevalence of Lewy bodies in the substantia nigra in a group of 273 control cases without Parkinson's disease and 121 cases of Alzheimer's disease. The substantia nigra was also studied in 14 cases of Downs syndrome, 13 of which had cortical Alzheimer pathology. No case of Down's syndrome had Lewy bodies. Counts of tangles and plaques in hippocampus, frontal and temporal cortex were lower in cases of Alzheimer's disease with Lewy bodies compared with those without, but cortical choline acetyltransferase (ChAT) activities were similar. The relatively small difference in the prevalence of Lewy bodies between controls and Alzheimer's disease could be explained by the additive effects of Lewy body and tangle pathology causing dementia, rather than a greater than chance association between Parkinson's disease and Alzheimer's disease.

Source: Gibb, W.R., Mountjoy, C.Q., Mann, D.M., & Lees, A.J. A pathological study of the association between Lewy body disease and Alzheimer's disease. Journal of Neurology, Neurosurgery & Psychiatry, 1989, 52, 701-708.

Lewy body pathology and Alzheimer disease in Down syndrome

Aging adults with Down syndrome (DS) develop Alzheimer disease neuropathology (AD) by the age of 40 years, primarily due to the overexpression of the amyloid precursor protein on chromosome 21. Lewy bodies (LBs) are observed in 7-60% of AD patients in the amygdala and in cortex. As we hypothesized that LB pathology would also be present in DS brain with similar locations and prevalence to AD, we evaluated the frequency of LB in a cohort of DS cases collected over the past 25 years. Neuropathology reports from 55 cases with DS were included in this study. We identified 6 cases (10.9%), all male, with a mean age of 57 years (SD=3) that showed LB and/or Lewy neurites. Five cases were BRAAK stage 6 and one was stage 5. The observation that all our LB positive cases were male may reflect a sample bias. In our study, Lewy pathology was most common in amygdala but other sites of involvement are seen similar to a prior DS study and AD studies. Prior DS studies (n=20-56 cases) found the frequency of LB pathology to range between 8-50% of cases being affected. The prevalence of LB in our DS cohort (10.9%) is in the low end of the range seen in other DS and AD studies.

Source: Movassaghi, M., Lou, J.J., Wright, S., Silva, J., Leavy, K., Kim, R., Monuki, E.S., Perez-Rosendahl, M., Head, E., & Yong, W.H. Lewy body pathology and Alzheimer disease in Down syndrome. American Journal of Clinical Pathology, 2022 Nov., 158(Supp 1), S33,

A case of Down's syndrome with diffuse Lewy body disease and Alzheimer's disease

Almost all Down syndrome (DS) patients over the age of 35 to 40 years have histologic features of Alzheimer's disease (AD). However, the presence of extrapyramidal features in up to 364 of these patients has no satisfactory pathologic explanation. We report an older patient with DS, dementia, and parkinsonian signs who showed pathologic changes of Parkinson's disease and cortical Lewy bodies in addition to AD. These parkinsonian changes may be related to chromosome 21 abnormalities.

Bodhireddy, S., Dickson, D.W., Mattiace, L., & Weidenheim, K.M. A case of Down's syndrome with diffuse Lewy body disease and Alzheimer's disease. Neurology Jan 1994, 44 (1) 159; DOI: 10.1212/WNL.44.1.159

The First Confirmed Case of Down Syndrome with Dementia with Lewy Bodies

Dementia with Lewy bodies (DLB) is the second commonest cause of dementia in the general population. Several researches have established an association between Down syndrome (DS) and Alzheimer’s disease. Very few studies have however showed such an association between dementia with Lewy bodies and Down syndrome. The occurrence of DLB in persons with DS is widely unrecognized. We report the first case of a person who fulfils the operational criteria for DLB and was also found to have Lewy bodies on neuropathological examination. It is important to make an early and accurate diagnosis as patients with DLB may respond differently than Alzheimer’s dementia patients to certain behavioural and medical treatments.

Source: V. P. Prasher, E. Airuehia, M. Carey. The first confirmed case of Down syndrome with dementia with Lewy Bodies. Journal of Applied Research in Intellectual Disability, 2010, 23(3), 296-300.

Detection of Lewy bodies in Trisomy 21 (Down's syndrome)

The presence of cortical senile plaques and neurofibrillary tangles sufficient to warrant a neuropathological diagnosis of Alzheimer's disease is well established in middle-aged individuals with Trisomy 21 (Down's syndrome). In contrast a relationship between Down's syndrome and Lewy bodies, one of the major neuropathological features of Parkinson's disease, has not been previously reported. In a clinico-neuropathological survey of 23 cases of Down's Syndrome, two patients, aged 50 and 56 years respectively, were found to have Lewy body formation in the substantia nigra in addition to cortical Alzheimer-type pathology. Neither case showed significant substantia nigra neuron loss although locus coeruleus loss was present in both. Since substantia nigra Lewy bodies are a characteristic neurohistological feature of idiopathic Parkinson's disease, their occurrence in cases of Down's syndrome with evidence of Alzheimer-type pathology supports an aetiopathological connection between Parkinson's disease, Alzheimer's disease, and Down's syndrome; and suggests that common pathogenic mechanisms may underlie aspects of neuronal degeneration in these three disorders, some of which may relate to aberrant chromosome 21 expression.

Source: Raghavan R, Khin-Nu C, Brown A, Irving D, Ince PG, Day K, Tyrer SP, Perry RH. Detection of Lewy bodies in Trisomy 21 (Down's syndrome). Can J Neurol Sci. 1993 Feb;20(1):48-51. doi: 10.1017/s0317167100047405. PMID: 8467429.

Dementia with Lewy bodies in Down's syndrome

The association between Down's syndrome (DS) and Alzheimer's disease is well established. This paper presents a review of the literature, suggesting a possible association between DS and the more recently recognised dementia with Lewy bodies (DLB). Patients with DLB frequently present with changes in affect and behaviour, and in particular with psychotic symptoms. The literature suggests a possible role for atypical neuroleptics in the management of psychosis in DLB.

Source: Simard M, van Reekum R. Dementia with Lewy bodies in Down's syndrome. Int J Geriatr Psychiatry. 2001 Mar;16(3):311-20. doi: 10.1002/gps.342. PMID: 11288166.

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