Unrevealing the sequence of dysphagia progression in ALS: an event-based, FEES-driven staging approach

Dysphagia drives morbidity and mortality in amyotrophic lateral sclerosis (ALS), yet staging systems treat it as a binary milestone and do not capture its trajectory. Reports diverge on the earliest abnormality, with some citing cohesive-bolus inefficiency and others thin-liquid impairment. Furthermore, how these findings relate to patient-perceived dysphagia remains unclear. In a prospective cohort, 78 incident ALS patients underwent one or more fiberoptic endoscopic evaluations of swallowing (FEES), yielding 108 assessments. Pharyngeal residue for four consistencies was rated with a validated scale. An event-based model (EBM) inferred the temporal order of abnormalities and defined a five-stage, FEES-based dysphagia staging system (DSS). Construct, convergent, discriminant, and prognostic validity were tested against established measures; responsiveness was assessed in patients with longitudinal FEES. The EBM identified a consistent sequence of swallowing impairment: solids, semisolids, liquids, saliva. Patient-perceived dysphagia occurred in 38% of DSS 1-2 evaluations versus 100% of DSS 3-4. The DSS showed construct validity by distinguishing bulbar- from spinal-onset ALS and convergent validity with the ALSFRS-R bulbar subscore and LMN bulbar score. Discriminant validity was supported by weak, non-significant associations with spinal/respiratory measures. Agreement with King's staging was moderate, and all King's stage IV patients mapped to DSS stages 3-4. The DSS was responsive to change (Stuart-Maxwell χ² = 11.034; p = 0.026). The EBM reconciles prior discrepancies: pathophysiology begins with solids, whereas symptom recognition typically coincides with liquid-phase residue. The FEES-based DSS is reproducible and clinically meaningful for tracking bulbar involvement and identifying higher-risk patients.