Poorer motor control associates with greater cognitive difficulties in people with Friedreich’s ataxia (FA), a study from Belgium suggests.
Its researchers also indicate that a recently validated cognitive test, although for a separate disease, ably captures the severity of problems with higher-level thinking in these patients, and could be used in FA clinical trials.
The study, “Cerebellar cognitive disorder parallels cerebellar motor symptoms in Friedreich ataxia,” was published in the Annals of Clinical and Translational Neurology.
Motor symptoms of FA are well characterized, and have generally been a research focus. Cognitive impairments, such as slower cognitive processing speed and difficulty in language- or vision-related tasks, are also common in this patient population.
Yet cognitive impairment in FA is often overlooked, partly because it tends to be subtle and not result in clear functional problems, but also because many common assessments cannot reliably detect intellectual difficulties in these patients.
Cognitive issues in people with FA are similar to those seen in another condition, cerebellar cognitive affective syndrome (CCAS). Recently, the CCAS Scale — “a pencil, and paper test that can be completed in less than 10 minutes” — was developed to rapidly assess cognitive impairment in CCAS patients.
The scale is composed of 10 tasks, including those related to counting, language, drawing, and suppressing inappropriate responses. Individuals who do not have CCAS are expected to pass all 10 tasks. Failing one task qualifies a person as “possible CCAS,” failing two corresponds to “probable CCAS,” and failing three or more constitutes “definite CCAS.”
Participants are assigned a non-diagnostic score based on how well each task is completed. The total possible score for all tasks combined ranges from 82 to 120 points.
Researchers at Université libre de Bruxelles evaluated 19 Friedreich’s ataxia patients (mean age, 30) using the CCAS scale. These people were also evaluated using the Scale for the Assessment and Rating of Ataxia (SARA), which looks at ataxia-related motor problems.
All patients, whose median disease duration was 15 years, failed at least one task on the CCAS. Three failed two items, and 12 failed three or more.
Participants who failed more tasks or had lower CCAS total scores had significantly higher SARA scores. In other words, results showed a statistically significant association between the extent of cognitive problems and the severity of motor impairment.
Failing more tasks on the CCAS scale, but not the total score earned, was associated with a longer disease duration.
“The positive correlation between the number of failed CCAS‐Scale items, disease duration and ataxia severity as assessed with the SARA, revealed a close link between motor and cognitive disturbances,” the researchers wrote.
“The characteristics of the CCAS‐scale, which defines CCAS in terms of failed items regardless of total raw score, explain why no significant correlation was found between raw scores and disease duration, even though raw scores provide a quantitative assessment of the patients’ performance that can be used for eventual follow‐up,” they added.
These scientists suggested that the link between motor and cognitive symptoms is likely due to impairment in the dentate nucleus, a brain region important for regulating both cognition and movement. Abnormalities in this region have previously been reported in people with FA.
“Our findings indicate that the CCAS‐Scale is a sensitive tool to quantify cognitive disturbances in [FA] and a potential outcome measure in clinical trials,” the researchers concluded.
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