Dementia due to diseases classified elsewhere

Diagnostic requirements

WHO clinical descriptions and diagnostic requirements [1,2].

Subcategories

• 6D85.0 Dementia due to Parkinson disease

  Dementia due to Parkinson disease develops among individuals with idiopathic Parkinson disease and is characterized by impairment in attention, memory, executive and visuo-spatial functions. Mental and behavioral symptoms such as changes in affect, apathy and hallucinations may also be present. Onset is insidious and the course is one of gradual worsening of symptoms. [1]

  • All diagnostic requirements for Dementia are met.
  • Dementia is presumed to be attributable to underlying Parkinson Disease, as demonstrated by neuropsychological test data, neuroimaging data, medical tests, family history, and/or clinical history.
  • Dementia Due to Parkinson Disease develops among individuals with idiopathic Parkinson disease and is often characterized by impairment in attention, memory, executive and visuo-spatial functions.
  • Behavioural and psychiatric symptoms such as changes in affect, apathy and hallucinations may also be present.
  • Onset is insidious and typically occurs one year of more after the development of parkinsonian motor symptoms. The course of dementia often follows that of underlying Parkinson’s disease (e.g., if Parkinson’s Disease gradually worsens, Dementia may gradually worsen).

  Note: A diagnosis of 8A00.0 Parkinson Disease should also be assigned.

• 6D85.1 Dementia due to Huntington disease

  Dementia due to Huntington disease occurs as part of a widespread degeneration of the brain due to a trinucleotide repeat expansion in the HTT gene, which is transmitted through autosomal dominance. Onset of symptoms is insidious typically in the third and fourth decade of life with gradual and slow progression. Initial symptoms typically include impairments in executive functions with relative sparing of memory, prior to the onset of motor deficits (bradykinesia and chorea) characteristic of Huntington disease. [1]

  • All diagnostic requirements for Dementia are met.
  • Dementia is presumed to be attributable to underlying Huntington Disease, as demonstrated by neuropsychological test data, neuroimaging data, genetic testing, medical tests, family history, and/or clinical history.
  • Dementia Due to Huntington Disease occurs as part of a widespread degeneration of the brain due to a trinucleotide repeat expansion in the HTT gene, which is transmitted through autosomal dominance.
  • Onset of symptoms is insidious typically in the third and fourth decade of life with gradual and slow progression.
  • Initial symptoms typically include impairments in executive functions with relative sparing of memory, prior to the onset of motor deficits (bradykinesia and chorea) characteristic of Huntington Disease.

  Note: A diagnosis of 8A01.10 Huntington Disease should also be assigned.

• 6D85.2 Dementia due to exposure to heavy metals or other toxins

  Dementia due to exposure to heavy metals and other toxins caused by toxic exposure to specific heavy metals such as aluminium from dialysis water, lead, mercury or manganese. The characteristic cognitive impairments in Dementia due to exposure to heavy metals and other toxins depend on the specific heavy metal or toxin that the individual has been exposed to but can affect any cognitive domain. Onset of symptoms is related to exposure and progression can be rapid especially with acute exposure. In many cases, symptoms are reversible when exposure is identified and ceases. Investigations such as brain imaging or neurophysiological testing may be abnormal. Lead poisoning is associated with abnormalities on brain imaging including widespread calcification and increased signal on MRI T2-weighted images of periventricular white matter, basal ganglia hypothalamus and pons. Dementia due to aluminium toxicity may demonstrate characteristic paroxysmal high-voltage delta EEG changes. Examination may make evident other features such as peripheral neuropathy in the case of lead, arsenic, or mercury. [1]

  • All diagnostic requirements for Dementia are met.
  • Dementia is presumed to be attributable to toxic exposure to specific heavy metals such as aluminum from dialysis water, lead, mercury or manganese, as demonstrated by neuropsychological test data, neuroimaging data, medical tests, and/or clinical history.
  • The characteristic neurocognitive impairments in Dementia Due to Exposure to Heavy Metals and Other Toxins depend on the specific heavy metal or toxin that the individual has been exposed to but can affect any cognitive domain.
  • Onset of symptoms is related to exposure and progression can be rapid especially with acute exposure.
  • In some cases, symptoms are reversible when exposure is identified and ceases.

  Note: An appropriate diagnosis from the grouping of NE61 Harmful Effects of or Exposure to Noxious Substances, Chiefly Nonmedicinal as to Source, Not Elsewhere Classified should also be assigned.

• 6D85.3 Dementia due to human immunodeficiency virus

  Dementia due to human immunodeficiency virus develops during the course of confirmed HIV disease, in the absence of a concurrent illness or condition other than HIV infection that could explain the clinical features. Although a variety of patterns of cognitive deficit are possible depending on where the HIV pathogenic processes have occurred, typically deficits follow a subcortical pattern with impairments in executive function, processing speed, attention, and learning new information. The course of Dementia due to human immunodeficiency virus varies including resolution of symptoms, gradual decline in functioning, improvement, or fluctuation in symptoms. Rapid decline in cognitive functioning is rare with the advent of antiretroviral medications. [1]

  • All diagnostic requirements for Dementia are met.
  • Dementia is presumed to be attributable to underlying Human Immunodeficiency Virus (HIV) Disease, as demonstrated by neuropsychological test data, neuroimaging data, medical tests, and/or clinical history.
  • Dementia Due to HIV may develop during the course of confirmed HIV disease, in the absence of a concurrent illness or condition other than HIV infection that could explain the clinical features.
  • Although a variety of patterns of neurocognitive deficits are possible depending on where the HIV pathogenic processes have occurred, typically deficits follow a subcortical pattern with impairments in executive function, processing speed, attention, and learning new information.
  • The course of Dementia Due to Human Immunodeficiency Virus varies and may involve gradual decline in functioning, improvement or resolution of symptoms, or fluctuation in symptoms over time.
  • Rapid decline in neurocognitive functioning is rare with the advent of antiretroviral medications.

  Note: An appropriate diagnosis from the Human Immunodeficiency Virus Disease grouping of the chapter on Certain Infectious or Parasitic Diseases should also be assigned.

• 6D85.4 Dementia due to multiple sclerosis

  Dementia due to multiple sclerosis is a neurodegenerative disease due to the cerebral effects of multiple sclerosis, a demyelinating disease. Onset of symptoms is insidious and not secondary to the functional impairment attributable to the primary disease (i.e., multiple sclerosis). Cognitive impairments vary according to the location of demyelination but typically include deficits in processing speed, memory, attention, and aspects of executive functioning. [1]

  • All diagnostic requirements for Dementia are met.
  • Dementia is presumed to be attributable to the cerebral effects of underlying Multiple Sclerosis, a demyelinating disease, as demonstrated by neuropsychological test data, neuroimaging data, medical tests, and/or clinical history. Cognitive symptoms are not primarily due to associated physiological or functional effects of the underlying disease (e.g., fatigue, motoric limitations).
  • Onset of symptoms is often insidious but may progress in a stepwise fashion in accordance with the underlying disease course.
  • Neurocognitive impairments vary according to the location of demyelination but typically include deficits in processing speed, memory, attention, and aspects of executive functioning.

  Note: A diagnosis of 8A40 Multiple Sclerosis should also be assigned.

• 6D85.5 Dementia due to prion disease

  Dementia due to prion disease is a primary neurodegenerative disease caused by a group of spongiform encephalopathies resulting from abnormal prion protein accumulation in the brain. These can be sporadic, genetic (caused by mutations in the prion-protein gene), or transmissible (acquired from an infected individual). Onset is insidious and there is a rapid progression of symptoms and impairment characterised by cognitive deficits, ataxia, and motor symptoms (myoclonus, chorea, or dystonia). Diagnosis is typically made on the basis of brain imaging studies, presence of characteristic proteins in spinal fluid, EEG, or genetic testing. [1]

  • All diagnostic requirements for Dementia are met.
  • Dementia is presumed to be attributable to underlying Human Prion Disease, as demonstrated by neuropsychological test data, neuroimaging data, genetic testing, medical tests, and/or clinical history.
  • Dementia Due to Prion Disease is caused by a group of spongiform encephalopathies resulting from abnormal prion protein accumulation in the brain. These can be sporadic, genetic (caused by mutations in the prion-protein gene), or transmissible (acquired from an infected individual).
  • Onset is insidious and there is a rapid progression of symptoms and impairment often characterized by neurocognitive deficits, ataxia, and motor symptoms (e.g., myoclonus, chorea, or dystonia).
  • Diagnosis is typically made on the basis of clinical presentation, brain imaging studies, presence of characteristic proteins in spinal fluid, EEG, and/or genetic testing.

  Note: An appropriate diagnosis from the grouping of Human Prion Diseases in the chapter on Diseases of the Nervous System should also be assigned.

• 6D85.6 Dementia due to normal pressure hydrocephalus

  Dementia due to normal pressure hydrocephalus results from excess accumulation of cerebrospinal fluid in the brain as a result of idiopathic, non-obstructive causes but can also be secondary to haemorrhage, infection or inflammation. Progression is gradual but intervention (e.g., shunt) may result in improvement of symptoms, especially if administered earlier in the course of the condition. Typically, cognitive impairments include reduced processing speed and deficits in executive functioning and attention. These symptoms are also typically accompanied by gait abnormalities and urinary incontinence. Brain imaging to reveal ventricular volume and characterize brain displacement is often necessary to confirm the diagnosis. [1]

  • All diagnostic requirements for Dementia are met.
  • Dementia is presumed to be attributable to underlying Normal Pressure Hydrocephalus, as demonstrated by neuropsychological test data, neuroimaging data, medical tests, and/or clinical history.
  • Dementia Due to Normal Pressure Hydrocephalus results from excess accumulation of cerebrospinal fluid in the brain as a result of idiopathic, non-obstructive causes but can also be secondary to haemorrhage, infection or inflammation.
  • Progression is gradual but intervention (e.g., shunt) may result in improvement of symptoms, especially if administered earlier in the course of the condition.
  • Typically, neurocognitive impairments include reduced processing speed and deficits in executive functioning and attention. These symptoms are also typically accompanied by gait abnormalities and urinary incontinence.
  • Brain imaging to reveal ventricular volume and characterize brain displacement is often necessary to confirm the diagnosis.

  Note: A diagnosis of 8D64.04 Normal-Pressure Hydrocephalus should also be assigned.

• 6D85.7 Dementia due to injury to the head

  Dementia due to injury to the head is caused by damage inflicted on the tissues of the brain as the direct or indirect result of an external force. Trauma to the brain is known to have resulted in loss of consciousness, amnesia, disorientation and confusion, or neurological signs. The symptoms characteristic of Dementia due to injury to the head must arise immediately following the trauma or after the individual gains consciousness and must persist beyond the acute post-injury period. Cognitive deficits vary depending on the specific brain areas affected and the severity of the injury but can include impairments in attention, memory, executive functioning, personality, processing speed, social cognition, and language abilities. [1]

  • All diagnostic requirements for Dementia are met.
  • Dementia is presumed to be attributable to an injury to the head, as demonstrated by neuropsychological test data, neuroimaging data, medical tests, and/or clinical history.
  • Dementia Due to Injury to the Head is caused by damage inflicted on the tissues of the brain as the direct or indirect result of an external force.
  • Trauma to the brain is known to have resulted in loss of consciousness, amnesia, disorientation and confusion, and/or neurological signs.
  • The symptoms characteristic of Dementia Due to Injury to the Head arise immediately following the trauma or after the individual gains consciousness and must include persistent cognitive impairments following any recovery of initial cognitive impairment that may be seen in the immediate post-injury period.
  • Neurocognitive deficits vary depending on the specific brain areas affected and the severity of the injury but can include impairments in attention, memory, executive functioning, personality, processing speed, social cognition, and language abilities.

  Note: A diagnosis of NA07 Intracranial Injury or one of its subcategories should also be assigned.

• 6D85.8 Dementia due to pellagra

  Dementia due to pellagra is caused by persistent lack of vitamin B3 (niacin) or tryptophan either in the diet or due to poor absorption in the gastrointestinal tract due to disease (e.g., Crohn disease) or due to the effects of some medications (e.g., isoniazid). Core signs of pellagra include dermatological changes (sensitivity to sunlight, lesions, alopecia, and oedema) and diarrhoea. With prolonged nutritional deficiency cognitive symptoms that include aggressivity, motor disturbances (ataxia and restlessness), confusion, and weakness are observed. Treatment with nutritional supplementation (e.g., niacin) typically results in reversal of symptoms. [1]

  • All diagnostic requirements for Dementia are met.
  • Dementia is presumed to be attributable to Pellagra, as demonstrated by neuropsychological test data, medical tests, and/or clinical history.
  • Dementia Due to Pellagra is caused by persistent lack of vitamin B3 (niacin) or tryptophan either in the diet or due to poor absorption in the gastrointestinal tract due to disease (e.g., Crohn disease) or due to the effects of some medications (e.g., isoniazid).
  • Core signs of Pellagra include dermatological changes (sensitivity to sunlight, lesions, alopecia, and edema) and diarrhea.
  • With prolonged nutritional deficiency neurocognitive symptoms that include aggression, motor disturbances (ataxia and restlessness), confusion, and weakness may be observed.
  • Treatment with nutritional supplementation (e.g., niacin) typically results in reversal of symptoms.

  Note: A diagnosis of 5B5C.0 Pellagra should also be assigned.

• 6D85.9 Dementia due to Down syndrome

  Dementia due to Down syndrome is a neurodegenerative disorder related to the impact of abnormal increased production and accumulation of amyloid precursor protein (APP) leading to formation of beta-amyloid plaques and tau tangles. APP gene expression is increased due to its location on chromosome 21, which is abnormally triplicated in Down syndrome. Cognitive deficits and neuropathological features are similar to those observed in Alzheimer disease. Onset is typically after the fourth decade of life with a gradual decline in functioning, and may impact 50% or more of individuals with Down syndrome. [1]

  • All diagnostic requirements for Dementia are met.
  • Dementia is presumed to be attributable to Down syndrome, as demonstrated by neuropsychological test data, genetic testing, medical tests, and/or clinical history.
  • Dementia Due to Down Syndrome is caused by abnormal increased production and accumulation of amyloid precursor protein (APP) leading to formation of beta-amyloid plaques and tau tangles. APP gene expression is increased due to its location on chromosome 21, which is abnormally triplicated in Down syndrome. Dementia Due to Down Syndrome may affect 50% or more of individuals with Down syndrome.
  • Neurocognitive deficits and neuropathological features are similar to those observed in Alzheimer Disease.
  • Onset is typically after the fourth decade of life and is often accompanied by a gradual decline in functioning.

  Note: A diagnosis of LD40.0 Complete Trisomy 21 (Down syndrome) should also be assigned.

References

1. World Health Organization. International Classification of Diseases, 11th Revision, for Mortality and Morbidity Statistics (ICD-11 MMS), 2026-01 release. World Health Organization; 2026.
2. World Health Organization. Clinical Descriptions and Diagnostic Requirements for ICD-11 Mental, Behavioural or Neurodevelopmental Disorders (CDDR). World Health Organization; 2024.

WHO text reproduced without changes from the WHO ICD-11 API. © World Health Organization, licensed under CC BY-ND 3.0 IGO. View this entry in the WHO ICD-11 browser.