Oral function tests in spinal muscular atrophy: closing the diagnostic gap in severely affected adult patients : A prospective observational study.

Purpose: In advanced stages of spinal muscular atrophy (SMA), established motor scores are unable to distinguish between the different degrees of remaining motor function. Bulbar muscles are affected at a later stage. The aim of the present study was to test whether oral function tests are able to better discriminate motor function than established scores and to replicate known associations between disease-related altered craniofacial anatomy and oral dysfunction in SMA.

Methods: A total of 43 adult individuals with SMA (mean age 39.7 ± 12; 25 men, 18 women) were included in this prospective, cross-sectional study. Oral function was measured using a piezoelectric sensor system and an Iowa Oral Performance Instrument (IOPI) device. Data from oral function tests and established motor scores were analyzed with regard to a possible floor or ceiling effect. It was tested to what extent SMA patients with different malocclusions presented with variable scores.

Results: Patients differed in ambulatory and treatment status (15 ambulatory vs. 28 nonambulatory; 35 treated vs. 8 nontreated) and orthodontic findings (22 with a class II molar relationship and increased overjet, 35 with posterior crossbite). In contrast to the oral function tests, some of the established motor scores showed a clear floor effect. Statistically significant associations were identified between reduced oral function values and an enlarged overjet, a class II molar relationship, and a posterior crossbite. This should be taken into account in neuromuscular evaluations.

Conclusion: In severely affected patients, oral function tests appear to be superior to established motor scores and fill a diagnostic gap in research and clinical practice.