Diagnostic Assessment and Classification of Acute Ischemic Stroke

I. Clinical Presentation and Initial Triage

Early recognition of stroke symptoms and precise timing are essential for reperfusion eligibility—time is brain.

1.1 Time of Onset and Last Known Well (LKW)

• Define LKW as the last moment the patient was at baseline neurologic function.
• Reperfusion windows:
  • IV thrombolysis: ≤ 4.5 hours from LKW
  • Mechanical thrombectomy: ≤ 6 hours (standard) and up to 24 hours with favorable imaging
• Rapid history techniques:
  • Ask witnesses for exact or approximate times of symptom onset or when patient was last seen normal.
  • In unwitnessed or wake-up strokes, use DWI/FLAIR MRI mismatch if available.

1.2 Focal Neurologic Deficits

• Common presentations referable to vascular territories:
  • Motor deficit: sudden hemiparesis or facial droop
  • Sensory loss: contralateral numbness or tingling
  • Language dysfunction: expressive or receptive aphasia
  • Visual field cut: homonymous hemianopia
  • Neglect or inattention
• Perform a concise stroke exam, ideally using the NIH Stroke Scale (NIHSS).
• Correlate deficit pattern with likely vessel territory (e.g., MCA vs. PCA).

1.3 Stroke Mimics

• Common mimics and distinguishing features:
  • Hypoglycemia: check bedside glucose; mental status may fluctuate
  • Seizures/postictal paresis (Todd’s palsy): witness history of convulsion, EEG if needed
  • Migraine aura: gradual onset, positive visual phenomena, headache history
  • Functional disorders: non-anatomic findings, inconsistency on serial exam

II. Laboratory Evaluation

Targeted labs confirm diagnosis, exclude contraindications, and inform initial management without delaying reperfusion.

2.1 Serum Glucose

• Mandatory in all suspected AIS prior to thrombolysis.
• Hypoglycemia (< 60 mg/dL): correct before any stroke‐specific treatment.
• Mild hyperglycemia common; maintain 140–180 mg/dL range but do not delay reperfusion for elevated glucose.

2.2 Coagulation Profile

• INR > 1.7 or aPTT prolonged: contraindication to IV tPA.
• In patients without anticoagulant use, do not wait for routine coagulation results before starting tPA.

2.3 Comprehensive Chemistries

• CBC: exclude thrombocytopenia (platelets < 100,000/µL).
• Electrolytes and renal/hepatic panels: guide contrast imaging safety.
• Cardiac biomarkers and lipid panel: plan secondary prevention once acute phase is addressed.

III. Neuroimaging Modalities

Imaging rapidly excludes hemorrhage, identifies large vessel occlusion (LVO), and estimates salvageable tissue.

3.1 Non-Contrast CT (NCCT)

• First-line to exclude intracranial hemorrhage.
• Early ischemic signs (often subtle): loss of gray–white differentiation, sulcal effacement, hyperdense vessel sign.

3.2 CT Angiography (CTA)

• Detects LVO in cervical and intracranial arteries.
• Collateral circulation grading predicts infarct progression and expansion of therapeutic window.

3.3 CT Perfusion (CTP)

• Maps cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT).
• Estimates core infarct (low CBF/CBV) vs. penumbra (prolonged MTT).
• Useful in extended window (6–24 hours) but may delay treatment if overused early.

3.4 MRI DWI/FLAIR

• DWI: highest sensitivity for hyperacute ischemia within minutes.
• FLAIR: changes appear after ~ 4–6 hours; DWI-positive/FLAIR-negative suggests onset < 4.5 hours.
• Limited by availability, patient stability, and contraindications.

IV. Severity Scoring and Etiological Classification

Standardized scales quantify stroke severity and guide prognostication; etiologic classification informs secondary prevention.

4.1 NIH Stroke Scale (NIHSS)

• 11 items, score 0–42; higher score = more severe deficit.
• Guides urgency: NIHSS ≥ 6 often prompts CTA for possible thrombectomy.
• Serial NIHSS detects early deterioration (e.g., hemorrhagic transformation).

4.2 TOAST Classification

• Subtypes: large‐artery atherosclerosis; cardioembolism; small‐vessel occlusion; other determined; undetermined.
• Requires vascular imaging, cardiac evaluation, and labs for accurate subtype assignment.
• Directs secondary prevention (e.g., anticoagulation for cardioembolic stroke).

4.3 Additional Scales

• ASPECTS on NCCT (10-point MCA territory score): < 6 suggests large core infarct, poor thrombectomy candidate.
• Modified Rankin Scale (mRS): baseline and follow-up functional status for outcome assessment.

V. Integration into Management Pathway

Combine clinical, lab, and imaging data into a streamlined code-stroke algorithm to minimize delays.

5.1 Risk Stratification

• High NIHSS + LVO + small core (ASPECTS ≥ 6) = top priority for endovascular therapy.
• Lower NIHSS without LVO = consider IV thrombolysis alone.

5.2 Clinical Decision Algorithm

Telestroke and teleradiology can expedite expert interpretation in resource-limited centers.

5.3 Reassessment and Monitoring

• Repeat NIHSS every 15–30 minutes during and after reperfusion therapies.
• Immediate imaging if clinical worsening occurs.
• Continuous cardiac monitoring for arrhythmias (e.g., atrial fibrillation).

VI. Pearls, Pitfalls, and Controversies

Be aware of common exam traps and emerging debates that may impact decision-making.

6.1 Overestimation of Deficits

• Distinguish dysarthria from aphasia and neglect from hemianopia to avoid NIHSS misclassification.

6.2 Extended Time Windows

• DAWN and DEFUSE-3 criteria allow thrombectomy up to 24 hours in select patients with mismatch.
• Applicability in community settings remains under evaluation.

6.3 Imaging Modality Selection

• Routine use of CTP in early window (< 6 hours) may prolong door-to-treatment time without clear benefit.
• In unstable patients or those with contraindications to MRI, CT-based protocols suffice.