What is the maximum NIH Stroke Scale score and does a left‑sided weakness score of 5 predict recovery after thrombolytic therapy (tPA)?

Maximum NIHSS Score and Prognostic Value of Left-Sided Weakness Score of 5

The maximum NIHSS score is 42, and a motor arm score of 5 (indicating complete paralysis/no movement) on the left side predicts poor recovery after thrombolytic therapy, though the overall baseline NIHSS score is a stronger predictor than any single component score.

Understanding the NIHSS Scale Structure

The NIHSS is an 11-item scale that assesses stroke severity through standardized neurological examination 1. The scale evaluates:

• Consciousness level (3 components: alertness, orientation, commands)
• Eye movements and visual fields
• Facial weakness
• Motor function (separate scores for left and right arm, left and right leg)
• Coordination, sensation, language, and attention

Maximum possible score: 42 points 2. The scale includes bilateral limb testing (both arms and both legs), which is why the maximum exceeds what might be expected from the 11 basic categories 1.

Interpreting Motor Arm Scores

For motor function assessment (Item 5), each arm is scored separately from 0-4 1:

• 0 = No drift
• 1 = Drift before 5 seconds
• 2 = Falls before 10 seconds
• 3 = No effort against gravity
• 4 = No movement at all

A score of 5 does not exist on the standard NIHSS motor arm scale—the maximum for any single limb is 4 (complete paralysis). If you're referring to a total motor score or different assessment tool, clarification is needed.

Prognostic Implications After Thrombolysis

Baseline NIHSS Score Predictions

Patients with baseline NIHSS <10 have 60-70% chance of favorable outcome at 1 year, while those with NIHSS >20 have only 4-16% chance 3, 1. A score <5 indicates a small stroke, while >20 indicates a large stroke 2.

Motor Weakness Severity

If a patient has a motor arm score of 4 (complete paralysis/no movement) on the left side:

• This contributes significantly to overall stroke severity
• Combined with other deficits, likely places the patient in a moderate-to-severe category
• The total baseline NIHSS score matters more than individual component scores for predicting recovery 4

Hemorrhage Risk Stratification

Patients with NIHSS ≥20 have 17% risk of intracranial hemorrhage after tPA, compared to only 3% risk in those with NIHSS <10 1. This is critical for informed consent and monitoring decisions.

Most Powerful Prognostic Indicators

24-Hour NIHSS Score is Superior

The 24-hour NIHSS score is the strongest predictor of 90-day functional recovery, outperforming baseline scores 4. Specifically:

• 24-hour NIHSS ≤4 predicts favorable outcome (mRS 0-2) with 66.5% sensitivity and 87.1% specificity (adjusted OR 9.44) 4
• 24-hour NIHSS ≤3 predicts excellent outcome (mRS 0-1) 4
• This is more predictive than baseline NIHSS or early change scores

Early Neurological Improvement

Early neurological improvement (ENI) at 2 hours—defined as NIHSS reduction ≥10 points or absolute score ≤4—independently predicts favorable 3-month outcomes (OR 2.536) 5.

Continuous neurological improvement (CNI) between 2-24 hours—defined as NIHSS reduction ≥8 points or score ≤4 at 24 hours—is an even stronger predictor (OR 7.253) 5.

Clinical Application Algorithm

For a patient with left arm complete paralysis (motor score 4):

1. Calculate total baseline NIHSS including all 11 components

   • If total <10: Expect 60-70% favorable outcome, 3% hemorrhage risk
   • If total 10-20: Intermediate prognosis
   • If total >20: Only 4-16% favorable outcome, 17% hemorrhage risk

2. Reassess at 2 hours post-tPA bolus

   • ENI (≥10 point drop or score ≤4) = strong positive predictor
   • No improvement = reassess management strategy

3. Reassess at 24 hours post-tPA

   • Score ≤4 = 9.4× higher odds of favorable recovery 4
   • Score >4 = adjust rehabilitation expectations and family counseling

4. Monitor for complications based on baseline severity

   • Higher baseline NIHSS = more intensive monitoring for hemorrhage
   • Serial neurological checks every 15 minutes × 2 hours, then hourly × 6 hours

Critical Caveats

• A single motor component score alone is insufficient for prognostication—always use the complete NIHSS
• Baseline NIHSS imbalances between treatment groups can confound trial results, but this doesn't diminish its clinical utility 6
• Women are twice as likely to show continuous neurological improvement between 2-24 hours 5
• The NIHSS was designed for anterior circulation strokes; posterior circulation strokes may score lower despite significant disability 7