Relationship between neurologic deficit severity and final functional outcome shifts and strengthens during first hours after onset

Abstract

Background and purpose: Early neurological deficit severity is the most important determinant of final functional outcome in acute ischemic stroke. However, deficit severity frequently changes during the first hours and days postonset.

Methods: Analysis of control group patients enrolled in the 2 National Institute of Neurological Disorders and Stroke tissue-type plasminogen activator trials. Neurological deficit severity was measured serially using the National Institutes of Health Stroke Scale (NIHSS) at 1 to 3 hours postonset, 3 to 5 hours, 24 hours, 7 to 10 days, and 90 days. Final global disability outcome was assessed at 90 days using the modified Rankin Scale.

Results: Among the 312 patients, median neurological deficit severity on the NIHSS improved throughout the 90-day observation period, from 15 (interquartile range, 9.5-20) at 1 to 3 hours, to 12 (interquartile range, 6-19) at 24 hours, to 7 (interquartile range, 2-19) at 90 days. Between 1-to-3-hours to 24 hours, more patients spontaneously improved than worsened: 39.1% versus 17.6% (P<0.001). NIHSS scores associated with individual final modified Rankin Scale global disability ranks shifted to lower values over time; eg, patients with a final modified Rankin Scale of 2 had the following median NIHSS scores: 12 at 1 to 3 hours, 10 at 3 to 5 hours, 9 at 24 hours, and 3 at 90 days. Correlation coefficients between NIHSS and the final modified Rankin Scale increased over time, from 0.51 at 1 to 3 hours, to 0.72 at 24 hours, to 0.87 at 90 days.

Conclusions: 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 decrease over time. Neurological deficit severity increasingly predicts final disability outcome, accounting for one quarter of the variance at 1 to 3 hours, one half at 24 hours, and three quarters at 90 days.

Figure 1

NIHSS score distributions at 1-3 hr, 3-5 hrs, 24 hr, 7-10 days, and 90 days in the placebo arms of the two NINDS-TPA trials. X axis is NIHSS score and y axis is percent of patients with that score. Most patients’ NIHSS scores begin shifting to lower values as early as 3-5 hours, continuing through 90 days. The minority of patients with fatal outcome and concomitant extremely poor NIHSS scores begin to appear after 24 hours and increase by day 90. Over time, the NIHSS median evolves from severe to moderate and the NIHSS distribution evolves from unimodal to bimodal.

Figure 2

Median NIHSS scores over time among surviving patients with different 3 month mRS global disability scores. The NIHSS scores associated with individual mRS ranks decline substantially over time. For IQRs, see Table 2.