Neurology and Stroke Calculators

The NIHSS quantifies stroke severity across 11 neurological domains: level of consciousness, gaze, visual fields, facial palsy, motor arm and leg, limb ataxia, sensory, language, dysarthria, and extinction/neglect. Scores range 0–42. Mild stroke: 1–4; moderate: 5–15; moderate-severe: 16–20; severe: 21–42. An NIHSS ≥6 generally supports consideration for mechanical thrombectomy; ≥4 (within 4.5 hours) supports IV tPA candidacy review.

The ABCD² score (Age, Blood pressure, Clinical features, Duration of TIA, Diabetes) estimates 2-day stroke risk after TIA. Low risk (0–3): ~1% 2-day risk; intermediate (4–5): ~4%; high (6–7): ~8%. However, AHA/ASA 2016 guidelines recommend urgent workup for ALL TIAs regardless of ABCD² score, including DWI-MRI and cardiac monitoring, because ABCD² alone does not safely identify low-risk patients for outpatient management.

Hunt-Hess grades clinical severity of subarachnoid hemorrhage: Grade I = asymptomatic or mild headache; Grade II = moderate-severe headache, nuchal rigidity, no neurological deficit; Grade III = drowsy/confused, mild focal deficit; Grade IV = stupor, moderate-severe hemiparesis; Grade V = deep coma, decerebrate posturing. Higher grades correlate with worse prognosis and guide timing of aneurysm treatment — Grade I–III typically undergo early surgical clipping or coiling.

The Fisher grade (CT-based) predicts vasospasm risk after subarachnoid hemorrhage: Grade 1 = no blood detected; Grade 2 = diffuse thin SAH (<1 mm); Grade 3 = localized clot or thick SAH (>1 mm) — highest vasospasm risk; Grade 4 = intracerebral or intraventricular clot. Modified Fisher grades (0–4) include bilateral subdural hematoma. Grade 3 and 4 warrant aggressive vasospasm surveillance.

The Canadian CT Head Rule applies to patients with minor head injury (GCS 13–15 after witnessed LOC, amnesia, or confusion). High-risk criteria (neurosurgical intervention needed): GCS <15 at 2 hours, suspected open/depressed skull fracture, signs of basal skull fracture, vomiting ≥2 episodes, age ≥65. Medium-risk criteria (brain injury on CT): retrograde amnesia ≥30 minutes, dangerous mechanism. The rule should not be applied to patients on anticoagulants or with pre-existing seizure disorders.

The GCS assesses eye opening (1–4), verbal response (1–5), and motor response (1–6), total 3–15. Serial GCS measurement is more informative than single assessment — a drop of ≥2 points indicates clinically significant deterioration. GCS ≤8 is conventionally used as a threshold for airway protection (intubation). The motor component (M score) is the most prognostically significant. Pediatric GCS uses age-adjusted verbal scoring.