Motor-dominant symptoms predict persistent neurological impairment in mild-to-moderate degenerative cervical myelopathy: a multi-state modeling study.

To characterize symptom domain-defined trajectories in mild-to-moderate degenerative cervical myelopathy (DCM) during scheduled non-operative follow-up, quantify transition probabilities and sojourn durations using a continuous-time multi-state Markov (MSM) model, and explore latent clinical heterogeneity through latent class analysis (LCA). This study is a secondary analysis of an existing multicenter randomized, double-blind trial dataset and does not evaluate comparative treatment effects. We conducted a secondary analysis of longitudinal data from a multicenter randomized, double-blind trial dataset (ChiCTR-INR-16009723) involving adults with mild-to-moderate DCM in the archived analytic dataset and complete Japanese Orthopaedic Association (JOA) domain data. The present analysis was restricted to the scheduled non-operative follow-up period and was designed to describe symptom-domain trajectories rather than treatment efficacy. Neurological status was classified into six mutually exclusive states based on JOA domains: asymptomatic; sensory-only impairment; isolated upper-extremity motor deficit; isolated lower-extremity motor deficit; combined upper- and lower-extremity motor deficits with normal bladder function; and sphincter involvement. Visits used in the present analysis took place at baseline; weeks 1, 2, 4, 6, and 8; and months 3 and 6. Transition intensities, 1-year transition probabilities, and mean sojourn lengths were estimated using a continuous-time MSM. Covariate effects (sex, age group, BMI category, prior conservative treatment, comorbidities) were modeled only for transitions meeting the prespecified ≥ 5-event threshold. LCA was performed using repeated state indicators across the scheduled visits to identify data-driven trajectory classes. This secondary analysis included only participants who remained on non-operative management throughout the analyzed follow-up period; patients who underwent surgery during treatment or follow-up were excluded at the data-screening stage. Ninety patients (mean age 58.6 years; 61.1% male) exhibited 71 observable state shifts, with the majority of assessments indicating stability. Sensory-predominant states exhibited considerable dynamism, characterized by frequent bidirectional transitions between asymptomatic and sensory-only states, with very brief mean sojourn durations (~ 0.25-0.31 years). Conversely, motor-dominant phenotypes exhibited enhanced short-term persistence; isolated lower-extremity motor deficits revealed the longest mean sojourn time (~ 2.76 years) and the highest one-year persistence (~ 71.9%). The advancement to more severe conditions over one year was infrequent (< 11%), but a significant proportion exhibited improvement from combined motor impairment to less severe stages. Covariate effects were largely unclear owing to limited occurrences; however, prior medication history and elevated BMI exhibited the most robust relationships with certain transitions. LCA supported a three-class solution (entropy ~ 0.99) including diverse longitudinal severity patterns, roughly differentiating between milder/fluctuating and more motor-dominant, more persistently severe trajectories. In non-operatively managed mild-to-moderate DCM, the clinical course during scheduled follow-up appeared non-linear and phenotype-dependent: sensory-only impairment tended to fluctuate with brief sojourn times, whereas motor deficits, especially lower-extremity motor deficits, were more persistent and showed limited spontaneous return to asymptomatic status. These exploratory MSM and LCA findings may help identify patients who warrant closer monitoring, but they should not be interpreted as establishing surgical timing thresholds or proving benefit from earlier intervention.