Coordination of smooth and effective movements is essential in daily tasks, such as speaking or walking. The ability to successfully orchestrate these movements is commonly referred to as “motor coordination”. While SCA patients can generally initiate movements with their bodies, their ability to execute these in a smooth and precise fashion is impaired. For instance, motor incoordination can be seen in a patient with ataxia’s inability to walk in a straight line, or in the difficulty they experience when swallowing. These and other motor function problems can greatly impact daily life. Assessing how well a patient can perform these movements provides an indication of how affected they are by the disease.
Unlike what’s measured with more familiar medical tests, such as blood pressure or levels of blood sugar, human movement cannot be quantified easily with clear numbers. To address this, multiple rates scales have been developed to help measure standardize motor coordination examinations. One of these scales is the Scale for the Assessment and Rating of Ataxia (SARA). An experienced clinician (typically a neurologist) evaluates a patient’s ability to perform a series of tasks (such as standing and walking) and then, using the SARA, assigns a score for each task. The process takes about 15-20 minutes, and typically involves the following tests:
- Gait (walking posture and ability): Patient walks a certain distance, turns, and continues walking
- Stance (ability to stand with or without support): Patient stands still in one spot in different poses
- Sitting: Patient sits for 10 seconds with arms outstretched
- Speech Disturbance: Examiner gauges how broken down or fluid a patient’s speech sounds during a casual conversation
- Finger Chase (coordination of movements): Examiner quickly moves finger in unpredictable directions while the patient tries to follow the movements with their own finger
- Nose-finger test (tremors and coordination of movements): Patient repeatedly moves finger from their nose to the examiner’s finger
- Fast, alternating hand-movements (coordination of movements):Patient performs 10 cycles of repetitive hand motions as fast as possible
- Heel-shin slide (coordination of movements): Patient lifts one leg, places heel on opposite leg’s knee, then slides heel down towards the ankle; usually done for both legs.
Each test yields a score, which is an estimate based on a scoring system designed to compare how close the movements/speech are to a person who does not have ataxia. Once a combined score is calculated, doctors will have an idea of how severe the disease is in the patient. A higher SARA score generally indicates more severe disease. This is used not only for diagnosis, but also to track how the severity of a patient’s ataxia symptoms changes over time. SARA scores can also be used to predict short-term patient outlook.
Even though the SARA allows researchers and doctors to measure symptoms using a standardized scale, it is not perfect. There is still room for improvement for how the scores are actually estimated. Several factors can affect the accuracy of the scale, such as patient age/underlying health problems, as well as variability in the way individual examiners assign scores.
Snapshot written by Dr. Claudia Hung and edited by Dr. Judit M. Perez Ortiz.