NIH Stroke Scale: Limb Ataxia Scoring Explained | Neurology Education

NIHSS scores guide critical stroke treatment decisions. For tPA thrombolytic therapy, scores of 5 or below indicate treatment benefits may not outweigh bleeding risks, while scores of 22+ suggest completed infarction with hemorrhage risk. Most facilities apply tPA for NIHSS 6-25 points. For mechanical thrombectomy, anterior circulation occlusion requires NIHSS ≥6 with ASPECTS ≥6, while posterior circulation requires NIHSS ≥10 with ASPECTS ≥6. NIHSS has limitations: floor effect (score 0 may miss significant MRI abnormalities), posterior circulation bias (underestimates vertigo/ataxia), and left hemisphere bias (language items favor left hemisphere strokes). These limitations should be considered in clinical decision-making.

The National Institutes of Health Stroke Scale (NIHSS) is a validated clinical tool scoring from 0 to 42 points to quantify stroke severity. Scores of 5 or higher typically qualify for thrombolysis, though lower scores may be acceptable if deficits are functionally incapacitating. The scale is reliable and reproducible with proper training. Thrombolysis eligibility requires age over 18, symptom onset within 4.5 hours, and NIHSS of 5 or higher. The risk-benefit trade-off involves potential neurological recovery versus bleeding risk. Each minute of delay reduces potential benefit, creating urgency in decision-making. Consent requirements are minimal: verbal consent suffices for capable patients, and treatment can proceed without family authorization for incapacitated patients.

Brain imaging is essential: non-contrast CT differentiates hemorrhagic (hyperdensity) from ischemic (hypodensity) stroke. Early ischemic CT signs include loss of gray-white matter differentiation, loss of insular ribbon, loss of lentiform nucleus density, and effacement of sulci. The NIH Stroke Scale (NISS) scores 0-42 points across 11 items evaluating consciousness, motor function, sensory function, visual function, language, and cognition. Scores of 1-4 indicate minor stroke, 5-15 indicate moderate stroke, and scores above 15 indicate severe stroke. Continuous monitoring includes vital signs, blood glucose, temperature, and neurological status. Blood pressure should be maintained above 180/105 mmHg during thrombolytic therapy and above 220/120 mmHg in non-thrombolyzed patients. Intravenous thrombolysis with rtPA is the standard acute stroke treatment, with standard dose 0.9 mg/kg (maximum 90 mg), 10% as initial bolus followed by 90% over 1 hour. Treatment must be initiated within 4 hours and 30 minutes of symptom onset. Age over 80 is no longer a formal contraindication.

Basic monitoring includes temperature (fever worsens outcomes), oxygen saturation (hypoxia worsens outcomes), blood pressure (hypotension worsens outcomes), and blood glucose (both hypo- and hyperglycemia worsen outcomes). Stroke mimics include hypoglycemia, postictal states, and migraine aura. Thrombolytic treatment (tPA) is first-line for eligible patients: onset within 4.5 hours, NIHSS score 4-25, no contraindications. Eligibility rate is 7-12%. ASPECTS score must be >7 for favorable outcomes. NIHSS provides objective severity assessment (0-42): 1-4 minor, 5-15 moderate, 15-20 severe, >20 very severe. Each point increase correlates with 17% worse prognosis. Rankin Scale assesses functional outcomes at 3 months.

NIHSS score thresholds for clinical decision-making: scores of 3-4 may indicate 'minor stroke' or 'stroke minor' (non-disabling). Scores of 10 or higher may indicate large vessel occlusion requiring thrombectomy consideration. Scores of 15 or higher indicate severe stroke. The NIHSS was originally derived from correlation with infarct volume measured 7-10 days after stroke, but has significant limitations for individual patient assessment. It is most useful for clinical trials and research, not for individual patient management.

Stroke localization involves correlating clinical signs with neuroanatomy and vascular supply to identify the site of infarction; key principles include understanding that lacunar syndromes arise from subcortical perforator occlusions (pure motor, pure sensory, sensorimotor, dysarthria-clumsy hand, ataxic hemiparesis, hemiballismus), cortical syndromes involve specific motor homunculus distributions (MCA supplying face/upper limb, ACA supplying lower limb/trunk), and brainstem syndromes produce characteristic cross-signs due to decussation of pyramidal and spinothalamic tracts, with posterior circulation syndromes potentially causing bilateral or generalized deficits requiring urgent recognition for improved outcomes.

Stroke localization is essential for diagnosis and treatment. Anterior circulation strokes (MCA, ACA) cause hemiparesis with arm/face predominance (MCA) or leg predominance (ACA), visual field defects, and cortical signs (aphasia, apraxia). Posterior circulation strokes (vertebral, basilar, PCA) cause vertigo, ataxia, cranial nerve palsies, and consciousness disturbances. Weber syndrome (PCA) shows ipsilateral CN III palsy with contralateral hemiparesis. Lateral medullary syndrome (vertebral) causes ipsilateral Horner's syndrome, ataxia, and crossed sensory loss. Stroke treatment follows a systematic algorithm: non-contrast CT to rule out hemorrhage, thrombolysis with tPA within 4.5 hours, CT angiogram for large vessel occlusion, and mechanical thrombectomy if indicated.

The brain receives dual blood supply: anterior circulation (carotid system: ACA, MCA) and posterior circulation (vertebrobasilar system: PCA). ACA irrigates medial brain including motor/sensory lower limb representations and supplementary motor area. MCA irrigates cerebral convexity including primary motor cortex, somatosensory cortex, Broca's/Wernicke's areas, and eye movement control. PCA irrigates occipital/temporal lobes including primary visual cortex. Syndromes are classified by vessel size (large vs. small/lacunar) and circulatory system (anterior/posterior). This anatomical-functional correlation allows clinicians to localize lesions and predict clinical manifestations based on vascular territory involvement.

Stroke localization requires understanding the circle of Willis anatomy, where the vertebral and basilar arteries supply posterior circulation (brainstem, cerebellum, thalamus, and medial temporal lobes), while the internal carotid artery supplies anterior circulation (ACA and MCA territories); ACA strokes cause contralateral cerebral monoparesis, urinary incontinence, and apathy-abulia, whereas MCA strokes produce contralateral hemiplegia, sensory loss, and language disturbances depending on dominant/non-dominant hemisphere involvement, with PCA strokes causing homonymous hemianopia with macular sparing, memory disturbances, and visual agnosia syndromes.

Stroke localization involves distinguishing between anterior circulation strokes (affecting the cerebral cortex via middle and anterior cerebral arteries) and posterior circulation strokes (affecting brainstem, cerebellum, and occipital lobe via vertebral and basilar arteries), with cortical strokes showing preferential motor involvement (face > arm > leg) due to the homunculus organization, while subcortical strokes show equal involvement of all limbs; lacunar strokes are small subcortical infarcts associated with hypertension, presenting as pure motor stroke (most common), pure sensory stroke, ataxic hemiparesis, or dysarthria-clumsy hand syndrome, and require MRI for detection since CT may be negative.

Stroke is defined clinically as an abrupt onset neurological deficit attributable to a focal vascular cause. It comprises two main types: ischemic stroke (85% of all strokes) from clot obstruction, and hemorrhagic stroke (15%) from bleeding. Critical to accurate diagnosis is recognizing stroke mimics that must be differentiated: hypoglycemia is the most common mimic and should be first investigated; seizures can present with residual weakness; migraines (hemiplegic type) can cause hemiparesis; venous sinus thrombosis and hypertensive encephalopathy also present similarly. The fundamental principle is that any acute focal neurological deficit should be considered stroke until proven otherwise, requiring systematic evaluation to avoid missing treatable conditions.

Stroke is fundamentally a clinical diagnosis based on history and examination, not imaging. Key stroke mimics include hypoglycemia (resolves with glucose), postictal paralysis (following seizures), and hemiplegic migraine. Subdural hematoma from minor trauma can also mimic stroke and is eminently treatable surgically. Recognition of these mimics prevents unnecessary investigations and inappropriate treatment while ensuring appropriate management of true stroke cases.

Several conditions can mimic stroke symptoms: metabolic disorders (hypoglycemia, hyponatremia, vitamin deficiencies) typically cause altered consciousness without focal deficits. Non-vascular focal deficits include focal seizures (Todd's paralysis), migraine aura, brain tumors, abscesses, and demyelinating lesions. These conditions lack the characteristic vascular distribution pattern of true stroke. The absence of vascular distribution is a key differentiating feature. Approximately 20% of patients with acute focal deficits may have stroke mimics rather than true stroke.

Stroke mimics include hypoglycemia (can present with all neurological symptoms), space-occupying lesions, CNS infections, metabolic disorders (especially sodium abnormalities), and drug intoxication. Hypertensive encephalopathy (BP >200/130 mmHg) presents with headache, nausea, vomiting, and confusion. Wernicke encephalopathy results from chronic thiamine deficiency, commonly in alcoholics or malnourished patients. All these conditions must be considered in the differential diagnosis of stroke.

Stroke mimics include meningiomas, subdural hematomas, hypoglycemia, syncope, seizures, and hypertensive encephalopathy. Hypoglycemia must always be ruled out before thrombolysis. Diagnostic workup includes glucose, ECG, toxicology, and cultures. CT scan is essential to rule out hemorrhage. MRI helps confirm ischemic stroke. The goal is to distinguish true stroke from mimics to guide appropriate treatment.