Oral functions found diminished in adults with SMA in study
Untreated SMA type 2 patients who couldn't walk had most oral impairment
Oral strength and endurance — important for functions like swallowing, speaking, and chewing — were found diminished in adults with spinal muscular atrophy (SMA) in three out of five assessments, according to a new study.
In particular, untreated SMA type 2 patients who couldn’t walk had the most impaired oral functions, including lower bite strength and endurance, while treated type 3 patients who could walk showed oral function comparable to healthy individuals.
“In the early clinical detection of [oral] dysfunctions, a reduced maximum mouth opening compared to healthy reference values can be detected even without complex measuring devices by the clinical provider and should lead to further investigations,” researchers wrote.
The study, “Oral functions in adult persons with spinal muscular atrophy compared to a healthy control group: a prospective cross-sectional study with a multimodal approach,” was published in the Orphanet Journal of Rare Diseases. The study was funded by Biogen, which markets the disease-modifying therapy Spinraza (nusinersen).
Muscle weakness and wasting (atrophy) are hallmark symptoms of SMA, a neurodegenerative disease that’s divided into five main types based on the patient’s age at symptom onset. Weakness usually affects the proximal muscles, or those closer to the center of the body, such as the muscles in the shoulders, thighs, and pelvis.
Progressive muscle weakness in SMA affects muscles needed for oral functions
Progressive weakness and degeneration also affect the bulbar muscles, or those of the mouth, throat, and face, that are needed for speaking, chewing, and swallowing. This can lead to reduced food intake and weight loss, poor oral hygiene, or a risk of choking or aspiration pneumonia, all of which can impact quality of life.
In this report, researchers in China compared the oral function of 45 healthy individuals to 58 adults with SMA, and took into consideration each patient’s SMA type, walking ability, and treatment status.
Of the patients, one (1.7%) was diagnosed with SMA type 1; 21 (36.2%) with type 2; 35 (60.3%) with type 3; and one (1.7%) with type 4. About 1 in 4 (27.6%) could walk (ambulatory).
Spinraza treatment was given to 38 patients (65.6%) starting at least six months before the study. Seven patients (12.1%) received Evrysdi (risdiplam), and 13 (22.4%) remained untreated.
Participants underwent oral function tests twice weekly during two separate visits. The researchers used various devices to measure mouth opening, bite force (maximum and endurance), and tongue strength (maximum pressure and endurance).
Analysis revealed SMA patients had moderate to severe malocclusions, or teeth that don’t fit together correctly when they bite. More than half had an overbite, or when the upper jaw is positioned further forward than the lower jaw, and some displayed an excessive overbite. Ten had an open bite, when the upper and lower teeth don’t touch when the mouth is closed.
In comparison, 29 healthy individuals had properly aligned jaws, 10 had an overbite, six had an underbite, or when the lower jaw is positioned further forward than the upper jaw, and five had an open bite.
Bite force endurance and maximum tongue strength were significantly lower in SMA patients than controls. Maximum mouth opening was also smaller in SMA patients. Maximum bite force and tongue strength endurance were similar between the two groups.
More oral function impairment seen in SMA type 2
SMA type 2 individuals had significantly lower maximum bite force, lower maximum tongue strength, and a smaller maximum mouth opening than those with SMA type 3. Bite force endurance was significantly higher in controls than in SMA type 2 and type 3 patients, whereas no difference was observed between the two SMA subgroups.
Nonambulatory SMA patients had significantly lower bite force endurance than the controls, as well as lower maximum tongue strength and a smaller maximum mouth opening compared with the controls and ambulatory patients. Tongue strength endurance showed no differences between the groups.
In terms of treatment, the maximum bite force was similar across all participants, while bite force endurance was significantly lower in the patients, regardless of treatment, than in the controls. Although tongue strength endurance was also similar across all groups, untreated SMA patients had lower maximum tongue strength and a smaller maximum mouth opening than healthy controls and treated SMA patients.
After controlling for the SMA type and walking ability of the patients, all treatment results remained unchanged, “suggesting a therapeutic effect of disease modifying therapies on oral function in adult persons with SMA,” the researchers wrote. “This comparison of oral function between persons with SMA and a healthy control group reinforces the existing evidence of diminished oral strength and endurance in SMA.”
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