Acute Stroke and the NIH Stroke Scale: The Evidence Behind the Pathway

A 64-year-old farmer from Brahmavar is brought to casualty by his son at 10 in the morning. He was well at 8. Now his left arm and leg are weak, his face droops on the left, and he does not seem to notice anything on his left side. The intern scores the NIH Stroke Scale: 7. “Only a minor to moderate stroke,” she says, and wonders whether the CT angiogram can wait. This is an illustrative case, not a real patient.

The NIHSS and Acute Stroke Pathway scores all 15 rows by the scale’s own rules and then routes the stroke: thrombolysis, thrombectomy, or neither. It keeps every rule, every dose and every caution. What it leaves out is the evidence behind them: the studies on the left and right asymmetry, on reliability, on the Indian bedside scores, on the Indian tenecteplase dose and on large-core thrombectomy. Those are here. By the end you will know why that score of 7 should not reassure the intern.

1. A 7 on the right is not a 7 on the left

The scale gives 7 of its 42 points to language, and 2 to neglect. Language belongs to the dominant hemisphere, usually the left. So the same amount of damaged brain scores lower on the right. Here is what the studies found.

“Does that change what we do?” It does, and exactly where it matters. The gap sits in the range where a rule such as “NIHSS 6 or more” decides who gets a vessel image. Our farmer has a right-hemisphere stroke and a score of 7. That is not a mild stroke. The tool’s advice is to get the vessel imaged and let the angiogram, not the number, decide.

2. Two good examiners, two different totals

The intern scored 7. Would the registrar score 7 too? Perhaps not.

Reliability is not uniform across the instrument. Certification restores agreement on the total, intraclass correlation above 0.95 in the TOAST programme, and leaves the individual rows as the residual disagreement.

• Lyden and colleagues, certification videos: limb ataxia is the worst row in the scale, kappa 0.21.
• Josephson and colleagues, 7,405 raters: best language and facial palsy contribute most to variance in the total, kappas 0.60 and 0.65.
• Same series: for 7 of 11 videotaped patients the total differed by four points or more between the fifth and ninety-fifth centile of raters.

A kappa measures agreement beyond chance: 1 is perfect, 0 is no better than guessing. So limb ataxia, at 0.21, is barely better than chance between examiners. The common mistake is to read a rise of four points as proof that the stroke has grown. Four points is the conventional definition of deterioration, but it sits inside the scale’s own noise between examiners. It should trigger a repeat scan and a reassessment, not a conclusion. That is why the tool asks you to score serially with the same examiner where the roster allows.

3. When there is no scanner: the Siriraj score in Indian hospitals

Many Indian stroke patients do not reach a scanner inside the treatment window. Bedside scores such as Siriraj try to separate a haemorrhage from an infarct without a CT. How well do they do here? Three Indian studies give an answer:

A positive likelihood ratio of 2.7 moves a probability very little. And notice the Chennai figure: Siriraj was equivocal in 17.3 per cent, so the published sensitivities overstate what the score does for an unselected patient at the door. The tool reports the equivocal band as an answer in its own right, and it keeps the Kolkata row with the Greek cut-off that its result uses.

4. The Indian tenecteplase dose

“Why does the tool print two doses of tenecteplase?” Because the American guideline gives 0.25 mg/kg to a maximum of 25 mg, and the Indian licence gives 0.2 mg/kg to a maximum of 20 mg. Which is right?

There has been no randomised comparison of the two. The evidence for the Indian dose is IRIS-TNK, a 1,015-patient single-arm safety registry mandated as a condition of approval and funded by the manufacturer, whose authors themselves call for a trial.

What IRIS-TNK showed. Symptomatic intracranial haemorrhage 0.6 per cent, three-month mortality 1.0 per cent, modified Rankin 0 to 2 at three months 75.1 per cent. Functional independence 93.4 per cent at NIHSS 7 or below, 70.9 per cent at 8 to 14, 46.4 per cent at 15 or above.

The same registry also showed how much the score itself matters. In IRIS-TNK, 1,015 thrombolysed patients, each additional point carried an odds ratio of 0.823 for a good outcome, ahead of age at 0.983 per year. In plain words, each extra point on the scale lowered the odds of a good outcome by about a sixth. A registry without a comparison group tells us the dose is used and how patients fare on it. It cannot tell us that it is better or worse than 0.25 mg/kg.

5. A large core, and the scan you actually have

A lower ASPECTS means a larger infarct. For years, a very low ASPECTS meant no thrombectomy. Six large-core trials between 2022 and 2024 moved that line: RESCUE-Japan LIMIT, SELECT2, ANGEL-ASPECT, TENSION, LASTE and TESLA. TESLA alone selected on non-contrast CT within 24 hours, the imaging reality in most Indian district hospitals, and missed its primary endpoint; TENSION used non-contrast CT but capped the window at 12 hours and was positive.

This is why the tool adds a caution to the Class 1 recommendation: where perfusion imaging is unavailable, the evidence for treating a very large core is weaker than the recommendation suggests.

6. Not every stroke is a stroke

Mimics account for close to half of hospital admissions for suspected stroke and 22 to 33 per cent of acute stroke activations in telestroke series. Seizure and the post-ictal state, migraine with aura, functional disorder and, above all, hypoglycaemia are the common ones. A glucose check at the door is never wasted.

Back to casualty

Our farmer’s score of 7 was a right-hemisphere 7, with neglect. The registrar did not wait. The CT showed no bleed, the angiogram showed a large vessel occlusion, and the team moved to treatment by the tool’s criteria. The intern learned what every stroke team learns once: read the score, then read the patient.

Try this

A 45-year-old woman has tingling down her right side for an hour, with no weakness. Her face is symmetrical, her pulse is regular, her systolic pressure is 138, and she has had seizures before. What does FABS say, and what do you do with it? Illustrative case.

Answer. FABS gives one point each for no facial droop, no atrial fibrillation, age below 50, systolic pressure below 150, a history of seizures and isolated sensory symptoms. She scores 6. Three or more identifies a mimic. But FABS was derived only in patients whose CT was already negative, so the tool raises it as a caution and it never withholds treatment. Scan her as you would anyone else.

Take-home points

• A right-hemisphere stroke scores lower than the same stroke on the left; image the vessel, and let the angiogram decide.
• A change of four points can be the examiner, not the stroke: repeat, rescan, and score with the same examiner where you can.
• Bedside stroke-type scores perform modestly in Indian hospitals; they never replace a CT.
• The Indian tenecteplase dose rests on a registry, not a trial; the tool prints both doses.
• A large core on plain CT alone is weaker ground for thrombectomy than the guideline’s class suggests.

Declaration: the author built and maintains the tool. It is free to use. The figures in this article are those the tool carried in its Evidence tab on 4 November 2026, each from the source the tool names. The illustrative cases follow the tool’s rules; check the tool’s result for a real patient.

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