The HD Measuring Stick: Assessment Standards for Huntington’s Disease
There are a number of well–established methods used to measure the severity and progression of Huntington’s disease (HD). These can evaluate a patient’s mental and physical capabilities and track any changes over time. Having standardized methods for measurement is important because it allows for the comparison of patients in clinical trials and the quantification of symptoms to guide treatment and therapy options.
Table of Contents
- Test Definitions
- Fahn Rating Scale (Physical and Mental)
- Unified Huntington’s Disease Rating Scale (UHDRS) (Physical and Mental)
- Zung Depression Scale (Mental)
- Mini–Mental State Examination (Mental)
- Barthel Index (Physical and Mental)
- Tinetti Scale (Physical)
- Physical Performance Test (Physical)
- Symbol Digit Modalities Test (SDMT) (Mental)
- Thurstone Word Fluency Test (Mental)
- Stroop Test (Mental)
- Neuropathological Scales
- For further reading
Each of the tests measures the subject’s abilities to perform various mental and physical functions in different ways. The tests are often used together, providing a more complete picture of the patient’s physical and cognitive well–being.
It is important to recognize that the pages in this article are intended only to give general information about some of the different tests used clinically and in research. We do not recommend the self–administration of these tests. Accurate administration of these tests requires qualified personnel such as doctors, therapists, and other trained professionals.
Fahn Rating Scale (Physical and Mental)^
The Shoulson–Fahn functional capacity rating scale was first proposed in 1979. It measures independence in daily activities such as dressing, eating, managing personal finances, and engagement in occupation. Functional capacity in each category is ranked from Stage 1 to Stage 5, with Stage 1 representing the most independent level of function. The table below summarizes the scale as it was originally proposed:
|Shoulson-Fahn Functional Capacity Rating Scale as Proposed in 1979|
|Engagement in occupation||Capacity to handle financial affairs||Capacity to manage domestic responsibilities||Capacity to perform activities of daily living||Care can be provided at|
|Stage 1||Usual level||Full||Full||Full||Home|
|Stage 2||Lower level||Requires slight assistance||Full||Full||Home|
|Stage 3||Marginal||Requires major assistance||Impaired||Mildly impaired||Home|
|Stage 4||Unable||Unable||Unable||Moderately impaired||Home or extended care facility|
|Stage 5||Unable||Unable||Unable||Severely impaired||Total care facility only|
This table was adapted from Shoulson and Fahn, 1979. See further reading.
The UHDRS is a standardized rating system used to quantify the severity of HD. Used clinically and in research, it measures the patient’s abilities in four general areas: motor, cognitive, behavioral, and functional. The different portions of the test may be administered separately.
The following table summarizes the individual categories tested in the motor section of the UHDRS:
|Ocular Pursuit||the ability of the patient to follow a finger with the eyes in both the horizontal and vertical directions|
|Saccade Initiation||the ability of the patient to turn the head in both the horizontal and vertical directions|
|Saccade Velocity||the speed at which the patient is able to turn the head both horizontally and vertically|
|Dysarthria||the presence of speech that is slurred, slow, and difficult to understand|
|Tongue Protrusion||the ability to stick out the tongue and the speed to which the task is completed|
|Finger Taps||the ability to tap the fingers of both hands (15 repetitions in 5 seconds is considered normal)|
|Pronation/Supination||the ability to rotate the forearm and hand such that the palm is down (pronation) and to rotate the forearm and hand such that the palm is up (supination) on both sides of the body|
|Fist-Hand-Palm Sequence||the ability to complete the sequence (making a fist, opening the hand palm down, and then rotating the hand palm up) more than 4 times in 10 seconds without cues is considered normal|
|Rigidity in arms||the severity to which the range of motion of the arms is limited|
|Bradykinesia||slowness in initiation and continuation of movements|
|Maximal Dystonia||abnormal muscle tone (measured separately in the extremities, face, and trunk)|
|Maximal Chorea||involuntary jerky movements of the body (measured separately in the extremities, face, and trunk)|
|Gait||walking with normal posture|
|Tandem Walking||the ability to walk in a straight line from heel to toe. The ability to do so regularly for 10 steps is considered normal|
|Retropulsion||the ability to stand after being pushed back|
In each category, patients are scored from 0 to 4, with 0 representing normal function, and 4 being the most severe dysfunction. The total score is the sum of the scores in the individual sub–categories. A higher UHDRS score indicates a more severe disease progression.
Zung Depression Scale (Mental)^
Patients with Huntington’s disease are significantly more likely to display signs of depression than people in the general population. Up to half of patients with HD demonstrate symptoms of depression. To learn more about the relationship between HD and depression, click here.
The Zung Depression Scale is a simple 20 item questionnaire. Patients judge statements about how they have been feeling on a qualitative scale ranging from “a little of the time” to “most of the time”. Each of the patient’s answers is then given a score from 1–4 and the sum of these scores is the total score. The range for total scores is between 20 and 80; patients with depression usually score between 50 and 69, while those with severe depression score above 70.
The scores and what they imply are summarized in the table below:
Mini–Mental State Examination (Mental)^
The Mini Mental State Examination (MMSE) assesses the overall cognitive status of patients. Its use is not limited to measurement of the progression of HD symptoms. For example, MMSE can also be used in the assessment of patients with other neurological diseases, such as Alzheimer’s disease.
It analyzes the patient’s abilities in 5 different areas of mental status: orientation, attention and calculation, recall, and language. Created in 1975, it is an effective 11–question test that only takes 5–10 minutes to administer and score. It has been used widely in both clinical practice and in research to measure the cognitive abilities of patients and subjects.
To test the patient’s orientation, he or she is asked what year, season, date, day, and month it is. He or she is then asked what state, country, town, hospital, and floor he or she is currently on.
Testing registration next, 3 objects are named, and the patient is given a chance to name all 3 of them. Assessing calculation abilities, patients are asked to count by 7′s.
Recall is tested by asking the patients to repeat the 3 objects he or she learned before.
Finally, language skills are tested in multiple parts. The patient is asked to name a pencil and watch, then is asked to repeat the phrase “No ifs, ands, or buts”. Next, he or she is asked to follow a verbal 3–stage command, and then a written command. Lastly, the patient is asked to write a sentence and copy the following drawing of two interlocking pentagons:
The successes and shortcomings of the patient are added up, and a total score is calculated. The maximum score on the MMSE is 30. Scores of 23 or lower are indicative of cognitive impairment.
Barthel Index (Physical and Mental)^
The Barthel Index (BI) is a commonly used scale to help assess the patient’s independence and his or her need for supervision or assistance. The test scores the patient’s ability to perform 10 basic daily living activities. Full credit for each criterion is not given if the subject needs even minimal help or supervision. The activities considered on this index include:
Scores for each individual item are given in increments of 5. The score for the items ranges from 5 to 15. The maximum total score is 100, and the higher the score, the more independent the patient.
Tinetti Scale (Physical)^
The Tinetti scale, also known as the Tinetti performance Oriented Mobility Assessment (POMA), is an easily administered test that measure’s a patient’s gait and balance abilities. The test takes approximately 10–15 minutes to complete and score.
The test is divided into two main parts, a balance portion and a gait portion. The patient’s balance in both the sitting and standing positions are measured. Additionally, the ability to stand from the sitting position and to sit down from standing up are quantified.
In the gait portion of the test, the subject is asked to walk across the room at a “normal” pace, and then back at a “rapid, but safe” pace. Various parts of the subject’s walk are noted, such as hesitation after being prompted to go, swing of the feet (height and path), step symmetry, step continuity, trunk sway, heel position, and smoothness of gait.
The test is scored on a 28 point scale. The indications for each score range are summarized in the table below. Scores ranging from 25–28 indicate a low fall risk, scores between 19 and 24 indicate a medium fall risk, and scores below 19 indicate a high risk for falls.
|0-18||High risk for falls|
|19-24||Medium risk for falls|
|25-28||Low risk for falls|
Physical Performance Test (Physical)^
The Physical Performance Test quantifies the subject’s performance in physical tasks. It is a standardized 9–item test that measures the subject’s performance on functional tasks:
Subjects are given two chances to complete each of the 9 items, and assistive devices are permitted for the tasks that require a standing position (items 6–9). Both the speed and accuracy at which the subjects complete the items are taken into account during scoring. The maximum score of the test is 36, with higher scores indicating better performance.
Symbol Digit Modalities Test (SDMT) (Mental)^
The Symbol Digit Modalities Test (SDMT) is a brief and simple mental test that takes less than 5 minutes to completely administer and score. The test measures the subject’s information processing speed and attention.
It involves a simple test in which numbers are randomly substituted for letters or geometric symbols. The subject is given a translation key, and is asked to translate them within 90 seconds. The task is easy for normal subjects to complete, but is more difficult for those patients with cognitive dysfunction.
The translation can be given in either a written or oral format. This flexibility in format allows for the testing of almost all subjects, including patients with speech or motor disorders. Additionally, the written format allows for the test to be administered to patients in a group setting.
Thurstone Word Fluency Test (Mental)^
The Thurstone Word Fluency Test (TWFT) is a simple test that measures the subject’s communication abilities. Given in either a written or oral form, the TWFT is commonly used to detect the presence of and define the nature of any cerebral dysfunctions.
First, the subject is given five minutes to write down or say as many words as possible that begin with the letter “s”. Next, he or she is given four minutes to list as many four–letter words as possible that begin with the letter “c”.
Several studies have shown that the TWFT is very accurate in identifying subjects with reduced cerebral function. However, the test is unable to identify which specific areas of the brain have been damaged. For example, the test can determine whether or not a patient has brain damage, but it cannot be used to detect whether the damage is on the left or the right side of the brain.
Despite its shortcomings, the TWFT is informative and is commonly used in combination with other tests to help gauge the presence and extent of brain damage in patients.
Stroop Test (Mental)^
The Stroop Test is a simple mental test commonly used to measure the subject’s attention and mental flexibility. It takes advantage of the Stroop effect, the interference that arises when the brain is presented with conflicting signals.
Patients are presented with a list of colors, like in the image below, each printed in a different color:
Next, the subject is asked to name the color of each word rather than what the word is. For example, the correct response to the first word in the third column would be “red” not “blue”.
The subject’s accuracy and speed at the Stroop Test can be recorded and used to track the progression of cognitive disabilities.
In addition to the tests discussed in this article, there are also various neuropathological grading systems which measure physical change in the brain as a result of the disease. One such scale that has been developed is the five–tiered pathological grading system, which rates damage done from Grade 0 to Grade 4, with Grade 4 having the most severe damage.
For further reading^
-A. Pipathsouk, 1-15-10