Parkinson's disease: mental changes
Although Parkinson's disease (PD) is primarily a movement disorder, it does affect other areas, including the psychological, behavioural and emotional aspects of a person. Depression may occur in people with PD as well as those with dementia and early-onset senility. Since the disease usually affects adults in their 50s and 60s, it is very difficult to assess whether these changes are due to the disease or are just part of the ageing process. This area of PD is, like the causes of the disease itself, not fully understood, and there are varying opinions across the medical world.
Cognitive abilities and difficulties
Cognition is the word which describes the mental processes involved in using language, knowing, learning, understanding, perceiving, attention, concentration, orientation, memory, initiation, planning, problem-solving, insight and judgement, mental flexibility (including abstraction and ability to change the topic), verbal fluency, cued recall and visuo-spatial recall.
People with PD have trouble performing 2 separate motor acts concurrently. They may also have difficulty processing 2 cognitive tasks simultaneously. Sleep deprivation and depression can also affect cognition. 'A lethargy of the mind' was first described in 1947 as a lack of interest, initiative, attention and concentration.
Now, in spite of the original description of PD as having no intellectual impairment, cognitive deficits are recognised, although they may not progress as rapidly as motor changes.
The symptoms vary and include memory loss and forgetfulness, bradyphrenia (slowness of thought processes), impairment of executive functions such as planning and problem solving, difficulty shifting among thoughts and problems running complex thought processes. An affected person may therefore appear forgetful and describe familiar activities in a disorganised and muddled way. Rigidity of thought may be noticed by others close to affected persons and by the persons themselves.
Anxiety
The frequency of anxiety disorders in PD is greater than that which would be expected for an older-age population. Anxiety usually appears after the diagnosis of PD but can also develop prior to the slowness and tremor associated with PD. This suggests that anxiety may not merely represent psychological difficulties adapting to the illness, but rather be linked to specific neurobiological processes occurring in PD. It is even possible that anxiety may represent the first sign of PD for some people. Whether anti-parkinsonian medications themselves contribute to anxiety needs to be clarified. There appears to be a strong relationship between movement difficulties and anxiety.
Most patients with 'on-off' fluctuations experience greater anxiety during the 'off' phase (when they are slower and more rigid).
It is unclear whether anxiety is an emotional reaction to difficulties with movement, whether anxiety might worsen these movement difficulties or whether both anxiety and poor mobility occur together as the result of common neurochemical mechanisms in the brain.
Memory loss
People with PD often complain of memory loss or impairment. Such tasks as remembering names, birthdays and shopping lists are often quoted as being the most difficult. However, memory function is sensitive to any factor which interferes with the workings of the central nervous system. Memory impairment can be an effect of drugs which act on the central nervous system, or result from brain damage or normal ageing. The problem is to distinguish between memory deficits due to PD and those caused by the natural process of ageing.
While memory may be affected, some tests that require a person to recall information given to them verbally show no apparent memory impairment. Other studies show impaired performance for free recall memory and yet no impairment in recognition memory in either verbal or visual tests. This suggests that a person with PD can recognise and store information but that problems occur when they are asked to recall it.
Dementia
The DSM-IV (American Psychiatric Association) states that the 'notion of clinical significance' is one of the primary criteria for the diagnosis of dementia. This means that the patient must have a 'loss of intellectual abilities of sufficient severity as to interfere with social or occupational functioning'. With PD this diagnosis is particularly hard, as the loss of motor control, evident in all people with PD, in itself interferes with daily functioning. Results may also be biased by: over-inclusion of the criteria for the diagnosis of dementia; failure to discriminate between dementia, confusional states, depression and even normal ageing; inclusion of patients without idiopathic PD (Brown and Marsden, 1988).
Studies so far do not show that dementia is an inevitable part of PD. However, they do show a somewhat higher incidence than the general population (10 per cent to 40 per cent). Dementia will inevitably contribute to impaired cognitive performance, but the precise nature of the cause of such impairments is as yet unknown.
Conditions with similar symptoms
Several rare conditions (such as Progressive Supranuclear Palsy, Huntington's chorea and Creutzfeld Jacob disease) mimic PD and also lead to severe dementia. Some drugs prescribed for psychiatric conditions can produce symptoms identical to those of PD.
Last Reviewed: 23 July 2002
