Spinal cord gray matter may be imaging marker of SMA types 2, 3
Study links shrinking gray matter to weaker muscles, worse motor function
Measuring the amount of gray matter in the spinal cord could help doctors track spinal muscular atrophy (SMA) over time and see how well treatments are working, according to a study that found shrinking gray matter was tied to weaker muscles and worse motor function.
More research is needed to confirm gray matter, the darker tissue found in the brain and spinal cord, “as a potential disease course and therapeutic response marker,” the researchers wrote in the study, “Spinal cord gray matter atrophy is associated with disability in spinal muscular atrophy,” published in the Journal of Neurology.
SMA is a genetic disease that weakens muscles over time, making it harder for people to move and do daily activities. It is mainly caused by mutations in the SMN1 gene that result in low levels of a protein needed for motor neurons, the nerve cells that control muscles, to survive.
Treatment options can change the course of SMA or affect the severity of its symptoms, but doctors need better ways to track how the disease is progressing and how well approved or experimental treatments are working. “There is still an unmet need for objective surrogate markers of disease progression in adolescent and adult patients with SMA, in whom motor disability usually worsens very slowly,” the researchers wrote. A surrogate marker is used as an indication of the effects of a specific treatment.
Imaging gray matter
The researchers, in Switzerland, used a method called radially sampled averaged magnetization inversion recovery acquisition to obtain detailed magnetic resonance images of the gray matter along the spinal cord.
Gray matter contains nerve cells that send signals to other parts of the body, including muscles. Measuring the amount of gray matter, and whether it shrinks over time, may give clues about how much damage SMA has caused to motor neurons.
The study looked at 21 adults with SMA (three with SMA type 2 and 18 with SMA type 3), with a mean age at SMA onset of 6.2 and a mean disease duration of 34.8 years, as well as 21 healthy adults of similar age and sex. All had rAMIRA imaging of their spinal cords at the level of the neck and lower back.
The spine consists of stacked bones called vertebrae. On average, the areas of gray matter in patients’ spinal cords were significantly smaller, by 13.6%–17.4%, than in healthy adults, except at the level of the second and third vertebrae in the neck.
Smaller gray-matter areas were linked to weaker muscles and lower scores on motor function tests, especially for tasks involving the arms. For example, the gray matter at the level of the third and fourth vertebrae explained 33% of the differences in the Revised Hammersmith Scale, which measures physical abilities.
“Further longitudinal investigations [done over time] are necessary next steps to evaluate the potential of this novel and easy to assess imaging marker for monitoring the disease course and therapeutic response in patients with SMA,” the researchers wrote.
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