DSM-IV

In DSM-IV, this disorder is called Dementia Due to Parkinson's Disease

For more information, see Dementia Due to Other General Medical Conditions

The essential feature of Dementia Due to Parkinson's Disease is the presence of a dementia that is judged to be the direct pathophysiological consequence of Parkinson's disease. Parkinson's disease is a slowly progressive neurological condition, characterized by tremor, rigidity, bradykinesia, and postural instability. Dementia has been reported to occur in approximately 20%-60% of individuals with Parkinson's disease and is more likely to be present in older individuals or those with more severe or advanced disease. The dementia associated with Parkinson's disease is characterized by cognitive and motoric slowing, executive dysfunction, and impairment in memory retrieval. Declining cognitive performance in individuals with Parkinson's disease is frequently exacerbated by depression. Findings on physical examination include the characteristic abnormal motor signs of resting tremor, evidence of slowness and poverty of movement (such as micrographia), or muscular rigidity and loss of associated movements. At autopsy, neuronal loss and Lewy bodies are evident in the substantia nigra. There are a number of syndromes that may manifest with dementia, parkinsonian movement disorders, and additional neurological features (e.g., progressive supranuclear palsy, olivopontocerebellar degeneration, and Vascular Dementia). Some individuals with Parkinson's disease and dementia are found at autopsy to have coexisting neuropathology indicative of Alzheimer's disease or of diffuse Lewy Body disease.

DSM-5

For more information, see Major and Mild Neurocognitive Disorders

Diagnostic Criteria

A. The criteria are met for major or mild neurocognitive disorder.

B. The disturbance occurs in the setting of established Parkinson's disease.

C. There is insidious onset and gradual progression of impairment.

D. The neurocognitive disorder is not attributable to another medical condition and is not better explained by another mental disorder.

Major or mild neurocognitive disorder probably due to Parkinson's disease should be diagnosed if 1 and 2 are both met. Major or mild neurocognitive disorder possibly due to Parkinson's disease should be diagnosed if 1 or 2 is met:

  1. There is no evidence of mixed etiology (i.e., absence of other neurodegenerative or cerebrovascular disease or another neurological, mental, or systemic disease or condition likely contributing to cognitive decline).
  2. The Parkinson's disease clearly preceded the onset of the neurocognitive disorder.

Differential Diagnosis

Major or mild neurocognitive disorder with Lewy bodies

This distinction is based substantially on the timing and sequence of motor and cognitive symptoms. For NCD to be attributed to Parkinson's disease, the motor and other symptoms of Parkinson's disease must be present well before (by convention, at least 1 year prior) cognitive decline has reached the level of major NCD, whereas in major or mild NCD with Lewy bodies, cognitive symptoms begin shortly before, or concurrent with, motor symptoms. For mild NCD, the timing is harder to establish because the diagnosis itself is less clear and the two disorders exist on a continuum. Unless Parkinson's disease has been established for some time prior to the onset of cognitive decline, or typical features of major or mild NCD with Lewy bodies are present, it is preferable to diagnose unspecified mild NCD.

Major or mild neurocognitive disorder due to Alzheimer's disease

The motor features are the key to distinguished major or mild NCD due to Parkinson's disease from major or mild NCD due to Alzheimer's disease. However, the two disorders can co-occur.

Major or mild vascular neurocognitive disorder

Major or mild vascular NCD may present with parkinsonian features such as psychomotor slowing that may occur as a consequence of subcortical small vessel disease. However, the parkinsonian features typically are not sufficient for a diagnosis of Parkinson's disease, and the course of the NCD usually has a clear association with cerebrovascular changes.

Neurocognitive disorder due to another medical condition (e.g., neurodegenerative disorders)

When a diagnosis of major of mild NCD due to Parkinson's disease is being considered, the distinction must also be made from other brain disorders, such as progressive supranuclear palsy, corticobasal degeneration, multiple system atrophy, tumors, and hydrocephalus.

Neuroleptic-induced parkinsonism

Neuroleptic-induced parkinsonism can occur in individuals with other NCDs, particularly when dopamine-blocking drugs are prescribed for the behavioral manifestations of such disorders.

Other medical conditions

Delirium and NCDs due to side effects of a dopamine-blocking drugs and other medical conditions (e.g., sedation or impaired cognition, severe hypothyroidism, B12 deficiency) must also be ruled out.

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