In Spinal Muscular Atrophy, Assess Mandibular Dysfunction Frequently
—Investigators assembled a Dutch cohort of SMA patients to assess reductions in mandibular function over time, finding that SMA type 2 patients suffered more severe limitations than those with SMA type 3a or 3b.
In patients with spinal muscular atrophy (SMA) type 2, mandibular movement and mouth opening ability decreased significantly over a 4-year period, according to the results of a prospective, longitudinal study.1
The investigators reported in their paper that “… the rates of decline may be more pronounced at younger ages,” leading them to suggest routine assessment and earlier intervention.
Impact of bulbar dysfunction studied
The Dutch team undertook this longitudinal study to assess the natural history of decreased active maximal mouth opening (AMMO) and other features of bulbar dysfunction in patients with SMA types 2 and 3 previously suggested in their cross-sectional studies.2,3
For the current study, the investigators recruited 60 patients with SMA types 2 and 3 at baseline between 2013-2014. The participants were brought back for follow-up examination between 2017-2018. Sixteen patients were lost to follow-up and therefore not included. The final study cohort comprised 22 patients with SMA type 2 (50%), 12 with type 3a (27%), and 10 with type 3b (23%). Mean age at baseline was 33.4 years, and a little over half were female (n=25). None of the patients received SMN-modulating medications prior to or during the study period.1
Bulbar function was assessed at baseline and 4 years with the Mandibular Functional Impairment Questionnaire (MFIQ) and a clinical exam of mandibular movement, including AMMO, bite force, and masticatory performance.
Mandibular difficulties observed in patients with SMA type 2
At the 4-year follow-up, the MFIQ revealed a significant increase in mandibular difficulties in patients with SMA type 2 but not in those with SMA type 3.
MFIQ mean score (standard deviation) baseline vs. follow-up:
- SMA type 2: 12.1 (12.8) vs. 16.1 (13.8), P<.001
- SMA type 3a: 7.2 (8.0) vs. 9.3 (9.0), P=.476
- SMA type 3b: 2.1 (2.3) vs. 3.3 (4.4), P=.385
Clinical examination at follow-up demonstrated a similar pattern, with significantly decreased AMMO in patients with SMA type 2 but not in those with SMA type 3.
Median AMMO reduction at follow-up:
- SMA type 2: 3.5mm (95% CI 2.3 to 4.7, P<.001)
- SMA type 3a: 1.5mm (95% CI –1.1 to 4.1, P=.236)
- SMA type 3b: 0.2 mm (95% CI –1.0 to 0.6, P=.591)
The investigators reported that “Decreasing AMMO over time is seen most often in patients with SMA type 2 with an estimated reduction of almost 1 mm per year.”
Annual mean decreases in AMMO:
- SMA type 2: 0.9 mm (95% CI -1.2 to -0.6, P<.001)
- SMA type 3a: 0.4 mm (95% CI -1.1 to 0.3, P=.230)
- SMA type 3b: +0.1 mm (95% CI -0.2 to 0.3, P=.585)
Of note, the investigators wrote, “Multivariate analyses show that [decreasing AMMO] particularly pertains to younger patients of this cohort, which supports the assumption that intervention strategies should start early.”
No significant changes were seen in voluntary bite force or masticatory performance.
Routine AMMO measurement and early intervention recommended
Based on their findings, the investigators encourage routine assessments of AMMO in patients with SMA, which they note is “easy, reproducible, and reliable.” The team also recommends starting orofacial exercises at a young age before patients experience reductions in AMMO.
“Future studies should include tests that can capture fatigability of the masticatory muscles, such as the 6-minute chewing test,” the authors concluded in their discussion.
Published:
References
.jpg)