Executive function deficits found in adult SMA type 3 patients: Study
Age at disease onset, motor function, anxiety, depression tied to the decline
Adults with spinal muscular atrophy (SMA) type 3 showed deficits in certain areas of cognition, particularly executive function or the ability to regulate one’s own actions, according to a recent study in Chinese patients.
Data from the small analysis suggest that these issues tend to be more pronounced in patients who cannot walk or who have mental health struggles.
“These preliminary findings expand our perspective on the understanding of the disease and may have implications for the management of SMA patients in clinical practice,” researchers wrote in the study, “Cognitive impairment in Chinese adult patients with type III spinal muscular atrophy without disease-modifying treatment,” which was published in Frontiers in Neurology.
SMA is characterized by the death and dysfunction of motor neurons (the nerve cells that control movement), which leads to symptoms of muscle weakness and atrophy. It’s generally thought that SMA doesn’t cause cognitive problems, though there is some controversy over whether and how SMA might affect the ways in which patients think. This could be either due to direct effects of the disease or because of differences in how SMA patients navigate the world.
To date, most studies assessing cognition in people with SMA have been done in Europe and North America. In this study, scientists conducted cognitive evaluations for people with SMA in China.
“To the best of our knowledge, this was the first study investigating potential cognitive alternations in Chinese adults with SMA,” the researchers wrote.
The study included data on 22 people with SMA type 3, as well as 20 people without SMA, who completed a battery of standardized cognitive tests.
In both groups most participants were men and levels of education were similar, though the SMA patients had notably more severe scores in measures of anxiety and depression. Roughly half of the SMA patients were able to walk while the rest relied on motorized wheelchairs to get around. All patients had normal speech and swallowing skills and none required help with breathing or feeding through a stomach tube. None of the patients had received any SMA treatments.
Variety of tests used to study cognition in SMA patients
Compared with individuals without the disease, SMA patients scored significantly worse on the Stroop Color and Word Interference Test. This is a common cognitive task where a person must read color words written in discordant colors (for example, the word “red” written in blue ink).
The SMA patients also had significantly worse scores in parts of the Verbal Fluency Test, a task where the participants had to think of as many words within a category as possible within a short space of time, as well as on the Wisconsin Card Sorting Test, where participants must use trial and error to make sense of a card-matching game to which they don’t know the rules.
Depression and anxiety scores as assessed by the Hamilton Depression Rating Scale and the Hamilton Anxiety Rating Scale were higher, meaning worse, in SMA patients compared with the healthy controls.
Among SMA patients, those who could walk tended to perform better on the card sorting test, which the researchers noted is suggestive of better executive function (the ability to regulate one’s own actions). A potential explanation for this finding might be that greater physical limitations lead to reduced development of executive function abilities, the researchers said, though they stressed it’s impossible to draw firm conclusions about cause and effect.
Patients with poorer scores related to executive function also tended to report worse mental health issues, the researchers noted.
Overall the decline in executive function was related to patients’ age at disease onset, motor function, anxiety, and depression.
These data show “it is important to monitor the presence of depression or anxiety in adult patients with SMA and to consider psychological interventions to reduce these feelings,” the scientists said.
In the Attention Network Test, a standardized assessment of attention abilities, SMA patients had poorer scores related to the executive control network, which refers to the ability to use working memory in a task to achieve a specific goal or solve a problem.
“These results showed that the SMA patients spent more time resolving conflicts compared to the healthy control group,” the researchers wrote.
Other measures generally didn’t show meaningful differences between individuals with or without SMA. The researchers stressed this study was limited to a small group of patients, so it’s impossible to draw any broad conclusions from these data alone and additional work is needed to understand fully how SMA affects cognition.
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