SMA treatment Spinraza eases fatigability in patients who can walk
Treatment with Spinraza (nusinersen) can help make walking less tiring over time for ambulatory patients with spinal muscular atrophy (SMA), a study reported.
The study, “Performance fatigability in adults with spinal muscular atrophy treated long-term with nusinersen,” was published in Muscle and Nerve.
SMA is marked by symptoms including muscle weakness and wasting. Many patients also experience a phenomenon called performance fatigability, where repetitive movements such as walking cause tiredness over time, which makes it hard to keep doing these movements for long stretches.
“Performance fatigability is increasingly recognized as an important and independent component of motor impairment in [persons with] SMA that has a relevant impact on activities of daily life,” the researchers wrote.
Spinraza was the first SMA treatment to become widely available. An abundance of data have shown that Spinraza can slow the progression of SMA and help patients retain greater muscle strength for longer. However, the therapy’s effects on performance fatigability haven’t been rigorously investigated.
Walking before and after SMA treatment
The researchers analyzed six-minute walk test (6MWT) scores from 14 ambulatory people with SMA before and after starting on Spinraza. The 6MWT is a common measure of exercise capacity in ambulatory people that simply tracks how far a person can walk in six minutes.
To assess performance fatigability, the researchers compared the distance walked during the first and last minutes of the 6MWT. If there was no performance fatigability, these measures would be expected to be essentially identical, whereas if there is performance fatigability, the latter would be smaller since patients would walk less as they tire.
Prior to starting on Spinraza, 12 of the 14 patients in the study showed evidence of performance fatigability: The distance walked in the last minute of the 6MWT was on average more than 13% shorter than the distance walked in the first minute. But after patients started on Spinraza, the extent of performance fatigability was lessened, by about 5.6% on average.
“We observed a reduction of [performance fatigability] with a mean change of 5.6%, suggesting a beneficial effect of [Spinraza] on [performance fatigability],” the researchers wrote.
Since performance fatigue usually gets worse over time in people with SMA who aren’t on treatment, this finding “indicates a potential long-term effect of [Spinraza] therapy on [performance fatigability],” the scientists wrote. However, they stressed a need for caution in interpreting the results from a small group of patients who were only followed for a few years, emphasizing the need for larger and longer studies.
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