Tongue ultrasonography as a quantitative biomarker for oropharyngeal dysphagia in neuromuscular disorders: a systematic review

Oropharyngeal Dysphagia (OD) is a prevalent and potentially life-threatening complication of Neuromuscular Disorders (NMDs). Tongue ultrasonography is an inexpensive, non-ionising, point-of-care technique that permits quantitative assessment of lingual muscle structure, but its value as a biomarker of OD across NMDs has not been systematically appraised. This systematic review aims to synthesize the available evidence on the diagnostic accuracy, reliability and clinical utility of quantitative tongue ultrasonography as a biomarker of OD in adults with NMDs. We systematically searched PubMed and Scopus for studies correlating quantitative tongue-ultrasound parameters, Tongue Thickness (TT) or Echo Intensity (EI), with instrumental swallowing assessment in adults with NMDs, following the PRISMA 2020 guideline. Study selection, data extraction and risk-of-bias appraisal were performed independently by two reviewers. Six studies (n = 10-38 per cohort) met the inclusion criteria. Reduced TT was a consistent marker of lingual atrophy in Amyotrophic Lateral Sclerosis (ALS) and correlated with oral-phase swallowing impairment, whereas functional measures of tongue strength were stronger predictors of aspiration risk. In Duchenne Muscular Dystrophy (DMD), increased TT reflected "pseudohypertrophy" from fatty and connective-tissue infiltration rather than preserved function and EI provided a complementary index of tissue quality in myopathic NMDs. Tongue ultrasonography is a promising, disease-sensitive biomarker for monitoring bulbar dysfunction in NMDs, but morphological indices should be integrated with functional swallowing data to predict aspiration risk. Standardized acquisition protocols and larger, longitudinal, multicentre studies are required before clinical implementation.