Abstract
People
with hemiparesis after stroke appear to recover 70% to 80% of the
difference between their baseline and the maximum upper extremity
Fugl-Meyer (UEFM) score, a phenomenon called proportional recovery (PR).
Two recent commentaries explained that PR should be expected because of
mathematical coupling between the baseline and change score. Here we
ask, If mathematical coupling encourages PR, why do a fraction of stroke
patients (the “nonfitters”) not exhibit PR? At the
neuroanatomical level of analysis, this question was answered by Byblow
et al—nonfitters lack corticospinal tract (CST) integrity at
baseline—but here we address the mathematical and behavioral causes. We
first derive a new interpretation of the slope of PR: It is the average
probability of scoring across remaining scale items at follow-up. PR
therefore breaks when enough test items are discretely more difficult
for a patient at follow-up, flattening the slope of recovery. For the
UEFM, we show that nonfitters are most unlikely to recover the ability
to score on the test items related to wrist/hand dexterity, shoulder
flexion without bending the elbow, and finger-to-nose movement,
supporting the finding that nonfitters lack CST integrity. However, we
also show that a subset of nonfitters respond better to robotic movement
training in the chronic phase of stroke. These persons are just able to
move the arm out of the flexion synergy and pick up small blocks, both
markers of CST integrity. Nonfitters therefore raise interesting
questions about CST function and the basis for response to intensive
movement training.
, David J. Reinkensmeyer, PhD
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