When cognitive decline is in direct consequence of Parkinson's Disease it is called Major or Mild Neurocognitive Disorder Due to Parkinson's Disease.
Firstly, the criteria needs to be met for either mild or major neurocognitive disorder, there is a gradual and insidious progression of impairment and the disorder is not better explained by another mental disorder or attributable to another medical condition. Major neurocognitive disorder includes a significant decline from a previous level of performance in either complex attention, executive function, learning and memory, language, perceptual-motor, or social cognitive based on concern of a person who knows the informant or the clinical; and the impairment is documented by a standardised neuropsychological test or another quantified clinical assessment. Lastly the cognitive deficit is not better explained by another medical condition. On the other hand, mild neurocognitive disorder is when the person has a modest cognitive decline from a previous level of performance and the deficits does not interfere with the ability to be independent but needs greater effort or compensatory strategies are needed to cope.
A probable diagnosis is given when there is no other contributing factor for the cognitive decline such as depression and when Parkinson's disease clearly precedes the onset of cognitive decline. A possible diagnosis is given when one of the two factors are present.
Parkinson's disease is a progressive neurological condition causing tremor, rigidity, bradykinesia, and postural instability. It occurs in approximately 20%-20% of individuals. Major or mild neurocognitive disorder due to Parkinson's disease is categorised by slow motor funciton (movement), slow cognition, executive dysfunction, and impairment in memory retrival.
Some people with Parkinson's disease may also have Alzheimer's disease, and Lewy body disease. They are then given the diagnosis of major or mild neurocognitive disorder due to multiple etiologies
American Psychiatric Association. (2013). Neurocognitive disorders. In Diagnostic and Statisical Manual of Mental Disoders DSM-5 (pp. 591-643). Arlington, VA: American Psychiatric Association.
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