Background:
Early neurologic deficit severity is the most important determinant of final functional outcome in acute ischemic stroke. Accordingly, in hospital quality performance measures and in clinical trials, deficit severity as assessed by an early NIH Stroke Scale (NIHSS) score is increasingly used to adjust outcomes for baseline prognosis/case mix. However, deficit severity frequently changes during the first hours and days post-onset.
Methods:
Analysis was performed of control group patients enrolled in the two NINDS TPA trials. Neurologic deficit severity was measured serially using the NIH Stroke Scale (NIHSS) at 1-3 hours post onset, 3-5 hours, 24 hours, 7-10 days, and 90 days. Final global disability outcome was assessed at 90 days using the modified Rankin Scale (mRS).
Results:
Among the 312 patients, median neurologic deficit severity on the NIHSS improved throughout the 90d observation period, from 15 (9.5-20) at 1-3h through 12 (6-19) at 24h to 7 (2-19) at 90d. Between 1-3h to 24h, more patients spontaneously improved than worsened, 39.1% vs 17.6% (p<0.001). NIHSS scores associated with individual final mRS global disability ranks shifted to lower values over time, e.g. patients with a final day 90 mRS of 2 had the following median NIHSS scores: 12 at 1-3h, 9 at 24h, and 3 at 90d (
Figure
). The correlation coefficient between NIHSS and the final mRS increased over time, from 0.51 at 1-3h through 0.72 at 24h to 0.87 at 90d.
Conclusion:
During the first 24 hours after onset, spontaneous improvement occurs in 2 of 5 acute ischemic stroke patients. The NIHSS scores associated with individual global disability ranks shift lower over time. Neurologic deficit severity increasingly predicts final disability outcome, accounting for one quarter of the variance at 1-3h, one half at 24h, and three quarters at 90d. It is desirable to consider timing of NIHSS assessment, in addition to the NIHSS score, when performing severity adjustment for performance measure reporting and clinical trials.
