February 2020: van der Vliet R, Selles RW, Andrinopoulou E-R, Nijland R, Ribbers GM, Frens MA, Meskers C and Kwakkel G. (Accepted manuscript) Predicting upper limb motor impairment recovery after stroke: a mixture model. Annals of Neurology, https://onlinelibrary.wiley.com/doi/abs/10.1002/ana.25679
Objective: Spontaneous recovery is an important determinant of upper extremity recovery after stroke, and has been described by the 70% proportional recovery rule for the Fugl‐Meyer motor upper extremity (FM‐UE) scale. However, this rule is criticized for overestimating the predictability of FM‐UE recovery. Our objectives were to (1) develop a longitudinal mixture model of FM‐UE recovery, (2) identify FM‐UE recovery subgroups, and (3) internally validate the model predictions.
Methods: We developed an exponential recovery function with the following parameters: subgroup assignment probability, proportional recovery coefficient rk, time constant in weeks τk, and distribution of the initial FM‐UE scores. We fitted the model to FM‐UE measurements of 412 first‐ever ischemic stroke patients and cross‐validated endpoint predictions and FM‐UE recovery cluster assignment.
Results: The model distinguished five subgroups with different recovery parameters (r1 = 0.09, τ1 = 5.3, r2 = 0.46, τ2 = 10.1, r3 = 0.86, τ3 = 9.8, r4 = 0.89, τ4 = 2.7, r5 = 0.93, τ5 = 1.2). Endpoint FM‐UE was predicted with a median absolute error of 4.8 IQR=[1.3 12.8] at one week post stroke and 4.2 IQR=[1.3 9.8] at two weeks. Overall accuracy of assignment to the poor (subgroup one), moderate (subgroups two and three) and good (subgroups four and five) FM‐UE recovery clusters was 0.79 95%ETI=[0.78 0.80] at one week post stroke and 0.81 95%ETI=[0.80 0.82] at two weeks.
Interpretation: FM‐UE recovery reflects different subgroups, each with its own recovery profile. Cross‐validation indicates that FM‐UE endpoints and FM‐UE recovery clusters can be well predicted. Results will contribute to the understanding of upper limb recovery patterns in the first six months after stroke.