It’s not just a movement disorder. Besides causing tremors and other motion-related symptoms, Parkinson’s disease affects memory, learning, and behavior.

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The Global Deterioration Scale is a global rating scale which is used to summarize whether an individual has cognitive impairments consistent with dementia (including Alzheimer's disease). Individuals are rated according to a seven-point scale, as outlined below; a score of 4 or higher is usually considered to be indicative of dementia. A score of 3 on the GDS is considered consistent with mild cognitive impairment (MCI); people with MCI are at heightened risk to develop dementia within the next few years.

GDS Rating:

1 = Patient has no complaints of memory deficit; clinician can detect no memory deficit evident during interview.

2 = Patient complains of memory deficit (forgetting names, forgetting where one has placed objects), but clinician can detect no objective evidence of a memory deficit during interview.

3 = Patient shows evidence of mild memory deficit during intensive clinical interview; symptoms include:

• patient may have gotten lost when traveling to a familiar location, may forget familiar names, may have problems finding the correct word
• family and/or co-workers are aware of memory lapses
• patient may have lost or misplaced an object of value
• patient may show anxiety and/or deficits in concentration

4 = Patient shows clear-cut evidence of memory deficit during interview with clinician, including decreased memory of current and recent events, decreased ability to travel or handle finances, inability to perform complex tasks. Patient may also deny there is any problem with his/her memory even though it is evident to friends and family.

5 = Patient can no longer handle activities of daily life without some assistance; patient is unable to recall a major aspect of current life such as own address or telephone number, and may have trouble choosing proper clothing to wear (e.g. deciding whether a coat is required).

6 = Patient is largely unaware of all recent events and experiences; may forget spouse's name, may become incontinent, may show personality changes.

7 = Patient loses all verbal abilities over the course of this stage; patient is incontinent and requires help with feeding and toileting; patient begins to lose basic motor skills (e.g. ability to walk).

Further Reading:

The GDS scale was originally presented by B. Reisberg, S. Ferris, M. de Leon and T. Crook ("The global deterioration scale for assessment of primary degenerative dementia," in American Journal of Psychiatry, vol. 139, pp/. 1136-1139.)