Identification, validation, and prediction of longitudinal recovery phenotypes in degenerative cervical myelopathy: analysis of prospective cohorts and a randomised controlled trial.

Background: Symptom evolution in degenerative cervical myelopathy (DCM) is traditionally characterized by severity of neurological deficit. A recent expert consensus challenged this view, proposing that DCM fluctuates across neurological, functional and health-related quality of life measures. We examined whether joint changes across these three domains define distinct recovery patterns in a clinic-based cohort of adult patients with DCM. Methods: Cohorts analysed were the Cervical Spondylotic Myelopathy-North America (CSM-NA, 2005-2007, N = 278), CSM-International (CSM-I, 2007-2011, N = 479) and the CSM-PROTECT Trial (2012-2017, N = 290). All participants were symptomatic adult DCM patients who underwent surgical treatment and completed at least three longitudinal assessments. Bayesian consensus clustering (BCC) was used to simultaneously model one-year changes in the modified Japanese Orthopaedic Association (mJOA), Neck Disability Index (NDI), and health-related quality of life (SF-36 Score). The optimal number of trajectory clusters was selected using maximum mean adjusted adherence. Multivariable logistic regression examined association between trajectory classes and achievement of minimal clinically important difference (MCID) across outcomes with internal validation performed using 100 bootstrap resamples. Findings: The final analytical cohort consisted of 1047 patients diagnosed with DCM. The mean age was 56.8 years, and 60.7% were male. The mean symptom duration was 29.8 months, and most patients exhibited involvement of two spinal levels. Joint modelling of multiple longitudinal outcomes resulted in three distinct patient groups. Trajectory 1 (n = 177, 17%) was characterised by minimal postoperative improvement with persistently low neurological function and health-related quality-of-life scores. Trajectory 2 (n = 524, 50%) demonstrated the greatest reductions in neck pain disability. Trajectory 3 (n = 346, 33%) exhibited global recovery, with substantial improvements across neurological, functional, and quality-of-life domains. Trajectory 3 patients had markedly higher odds of achieving MCID in neurological function (odds ratio [OR] 10.90, 95% CI 6.15-19.32), physical quality of life (OR 7.32, 95% CI 3.53-15.22), and disability (OR 3.02, 95% CI 1.85-4.93) compared to patients in Trajectory 1. BCC-derived models reduced clustering uncertainty and improved model discrimination beyond conventional outcome predictors. Predictors of global recovery included an anterior surgical approach (OR 3.55, 95% CI 1.21-10.37) and higher baseline frailty (OR 1.42, 95% CI 1.14-1.76). Interpretation: We provide evidence that outcomes in DCM follow three distinct, multidimensional trajectories that are not captured by neurological severity alone. Simultaneous assessment of neurological, functional, and health-related quality-of-life outcomes is both valid and informative, enabling phenotypic stratification and improved longitudinal prognostication in DCM. External validation of these recovery phenotypes in independent DCM cohorts is warranted. Funding: None.