The inability to draw a clock is a classic sign of dementia, often used by doctors as part of cognitive testing. But why is this simple task so difficult for those with dementia? In this article, we will explore the clock drawing test and look at the cognitive functions it assesses. We will also discuss the types of dementia that lead to clock drawing impairment and explain what a normal vs abnormal clock drawing looks like. By the end, you will have a better understanding of this important dementia evaluation tool.
What is the Clock Drawing Test?
The clock drawing test (CDT) is a quick, effective way to evaluate a person’s cognitive functioning and screen for dementia or other neurological disorders. During the CDT, the patient is given a blank piece of paper and asked to draw the face of a clock, put in all the numbers, and set the hands to a specific time. This simple task assesses multiple cognitive domains including:
- Visual memory and spatial reasoning – recalling the layout and placement of numbers on a clock face
- Planning and organization – sequencing and spacing numbers correctly
- Abstract thinking – translating verbal instructions into the visual representation of a clock
- Executive function – shifting between clock components
- Visual constructional skills – drawing the clock face and hands
Impairment in any of these abilities will result in an abnormal CDT performance. As such, the CDT allows clinicians to screen patients for cognitive dysfunction and identify the areas that may be affected. It is often used in conjunction with other assessments to help diagnose dementia subtype and disease severity.
CDT Performance in Different Dementia Types
Not all dementias affect clock drawing ability to the same degree. Performance on the CDT can provide clues as to the type of dementia a patient may have.
Alzheimer’s Disease
Alzheimer’s disease typically causes significant visuospatial and constructional deficits. Alzheimer’s patients often have trouble accurately spacing the numbers on the clock face or drawing the hands to show the instructed time. Overall, the CDT has a high sensitivity for detecting Alzheimer’s dementia. Patients tend to show impaired performance that correlates with disease severity.
Vascular Dementia
Vascular dementia results from strokes or small vessel disease in the brain. Visual-spatial skills and executive functions like planning can be affected. Patients with vascular dementia may draw overly-small numbers, neglect to put numbers on one side of the clock, or draw contour errors on the clock face.
Lewy Body Dementia
Dementia with Lewy bodies impacts visuospatial abilities, attention, and executive functions. Clock drawings tend to be disorganized and spatially distorted. Problems with visual hallucinations may also lead patients to add bizarre or inappropriate details outside the actual clock face.
Frontotemporal Dementia
Frontotemporal dementia typically spares drawing and constructional skills in its early stages. Patients can often complete a normal-appearing CDT at first. However, executive dysfunctions like poor planning and mental flexibility tend to emerge as the disease progresses. This can result in mild CDT abnormalities later on.
Features of a Normal Clock Drawing
When assessing a CDT, there are certain features that indicate normal cognitive functioning:
- The clock face is a complete large circle with no missing sections or distortions.
- All 12 numbers are present without omissions or duplications.
- The numbers are evenly spaced around the clock face.
- Number sequencing is correct with the numbers in the right order and direction.
- The numbers 12, 3, 6, and 9 are placed in the proper anchor positions.
- The hands display the correct time as instructed and are the appropriate relative lengths.
- No perseveration or unnecessary details are present.
Meeting all these criteria results in a perfect score. Here is an example of a normal clock drawing:
Abnormalities Seen in Dementia
Patients with dementia deviate from the above criteria in ways that reflect their underlying cognitive deficits. Here are some common characteristics of abnormal clock drawings:
Spatial and Constructional Errors
– Misplacing or omitting numbers
– Inaccurate spacing between numbers
– Drawing outside the predrawn circle
– Distortions or perseverations of the circle contour
– Erroneous hand lengths or positions
Planning and Executive Dysfunction
– No planning on spacing of numbers
– Random or counter-clockwise numbering
– Perseverative patterns like repeating groups of numbers
– Loss of structure from missing anchor points
– Difficulty switching between clock components
Memory Impairment
– Forgetting or confusing the instructed time
– Losing place in the numbering sequence
– Working memory overload results in incomplete drawing
Agnosia and Loss of Abstract Thinking
– Inability to represent clock concept with concrete examples like “sun”, “plate”, etc.
– Adding literal interpretations like hands, arms, face to the clock
Visuospatial Disorganization
– Numbers crowded on one side of the clock
– Tilting or skewing of the clock face
– Closing numbers towards the center
Here is an example of an abnormal clock drawing seen in dementia:
Scoring Clock Drawings
Various scoring systems exist to objectively rate the CDT, with higher scores indicating more impaired performance. Two common scales are:
Sunderland Scale
Uses a 10-point quantitative scale assessing:
- Contour – 2 points
- Numbers – 4 points
- Hand placement – 4 points
Scores range from 0 (perfect) to 10 (highly impaired). Scores above 2 indicate dementia.
Wolf-Klein Clock Drawing Scale
Divides drawings into 5 qualitative categories:
- Stage 1: Perfect clock = No errors
- Stage 2: Minor visuospatial errors
- Stage 3: More visuospatial disorganization
- Stage 4: Moderate impairment with loss of clock concept
- Stage 5: Severe cognitive impairment
Stages 3-5 are highly correlated with dementia.
Role in Dementia Evaluation
The clock drawing test is advantageous because it is:
- Brief and easy to administer taking only about 5 minutes
- Well-tolerated by patients as a non-threatening task
- Sensitive for detecting moderate to severe dementia with 70-90% accuracy
- Useful for tracking disease progression over time
- Capable of distinguishing Alzheimer’s from other dementias
- Effective even in low-literacy populations
Due to these assets, the CDT is commonly used as a:
- Standard part of cognitive screening tests like the MoCA
- Standalone assessment tool for dementia
- Measure of spatial, constructional, and executive functions
- Means of gauging disease severity and monitoring decline
However, it cannot diagnose dementia on its own and results must be considered within the full clinical context.
Early Detection
The CDT can detect cognitive impairment quite early. Individuals with mild cognitive impairment or very mild but clinically significant dementia are still likely to exhibit some abnormalities when drawing a clock. Visuospatial and executive deficits emerge early on. The CDT can help identify these initial signs of neurodegeneration for further evaluation.
Distinguishing Dementia Types
As discussed previously, the characteristic pattern of errors can indicate certain dementias. Diffuse visuospatial disorganization points to Alzheimer’s disease as the likely pathology. Problems maintaining structure with low planning suggest frontotemporal dementia. Repeating loop patterns may indicate Lewy body dementia. The CDT provides useful diagnostic clues.
Staging Severity
More severe dementia produces greater CDT impairment. Assessing both the type of errors and overall performance level allows clinicians to rate the current stage of the dementia. Sequential clock drawings done periodically enable tracking of progression over time.
Limitations
While very useful, the clock drawing test does have some limitations. These include:
- Low specificity – Abnormal CDTs also occur in other neurological disorders besides dementia, such as stroke or Parkinson’s disease.
- Difficulty detecting slight declines – Mild worsening in early disease may not result in notable CDT changes.
- Less effective in advanced dementia – Floor effects come into play as abilities diminish.
- Language barrier – Requires good comprehension of verbal instructions.
- Education bias – Illiterate individuals may do poorly regardless of cognitive status.
- Limited functions tested – Assesses only certain cognitive domains.
Due to these caveats, clinicians always integrate CDT results with other data like patient history, brain imaging, and lab tests to make diagnostic and treatment decisions regarding dementia. It serves as an adjunct assessment tool rather than a standalone diagnostic.
Conclusion
In summary, the clock drawing test provides a quick, convenient way for clinicians to screen cognitive function and uncover visuospatial or executive impairment suggestive of dementia. It cannot diagnose by itself, but serves as a useful component of the clinical workup. When interpreted carefully alongside other information, the CDT allows medical providers to accurately detect dementia, better determine the subtype and severity, and monitor any worsening over time. While limited in some aspects, it offers valuable insights into a patient’s skills and deficits. The simple task of clock drawing can reveal much about the status of cognition in aging individuals.
