Impairment of lip and tongue strength in symptomatic SMA1 patients: Results from a 4-center prospective study using the IOPI.

BACKGROUND

Spinal muscular atrophy (SMA) is a genetic neuromuscular disease characterized by muscular atrophy and respiratory and bulbar dysfunction, especially in the most severe phenotypes (SMA type 0 and 1). Swallowing function remains understudied because assessment tools are often unavailable or poorly tolerated by young children. The Iowa Oral Performance Instrument (IOPI), that measures orofacial strength via a small air-filled bulb has recently been evaluated in SMA type 2 and 3 patients.

OBJECTIVE

The purpose of this study was to investigate muscle strength of several muscles used during the oral phase of swallowing using IOPI in SMA type 1 children treated with nusinersen compared to healthy controls. In addition, it sought to correlate labial and lingual pressures with known key predictors of phenotype severity (Children's Hospital Of Philadelphia Infant Test of Neuromuscular Disorders [CHOP INTEND], age at first symptoms, SMN2 copy number) and indicators of feeding-nutritional status (p-FOIS (Pediatric Functional Oral Intake Scale)).

METHODS

Combining results from four independent centers, we recruited 22 individuals with a confirmed genetic diagnosis of symptomatic SMA type 1. All patients had been treated with nusinersen for at least 2.5 years and had undergone at least one IOPI measurement at a median age of 5.4 years. IOPI data were compared to age- and gender-matched controls and published normative data when available.

RESULTS

Oral pressures were lower in patients than in typically developing children (lips: p < 0.01; tongue: p < 0.001). Weaker labial pressure was significantly correlated with younger age at disease onset (r = 0.66; p = 0.0053), older age at first nusinersen injection (r = -0.52; p = 0.0326), lower body mass index (r = 0.61; p = 0.0149), and worse motor performance as expressed by the CHOP INTEND score (r = 0.60; p = 0.0170). Weaker tongue pressure was significantly correlated with younger age at disease onset (r = 0.49; p = 0.0372) and lower p-FOIS (r = 0.526; p = 0.022).

CONCLUSIONS

IOPI measurements objectively demonstrate orofacial weakness in this population compared with healthy controls and may serve as a biomarker to monitor the impact of comprehensive management, including disease-modifying therapies, on oral swallowing function in SMA type 1.