What are the appropriate steps to take when experiencing new onset left arm numbness?

New Onset Left Arm Numbness: Immediate Assessment and Management

New onset left arm numbness requires immediate emergency evaluation to rule out acute stroke or acute arterial occlusion—both life-threatening conditions requiring intervention within minutes to hours to prevent permanent disability or death. 1, 2, 3

Immediate Critical Differentiation

The first priority is distinguishing between two emergent diagnoses:

Check for Acute Arterial Occlusion FIRST

• Immediately assess the radial pulse on the left arm 2
• Measure blood pressure in both arms—a difference >20 mmHg confirms significant arterial compromise 2
• Assess the "6 P's": Pain, Pallor, Pulselessness, Paresthesias (numbness), Poikilothermia (cool limb), Paralysis 2
• If pulse is absent or blood pressure unmeasurable on the left side, this is acute arterial occlusion requiring immediate vascular surgery consultation 2

If Pulse is Present, Assume Stroke/TIA Until Proven Otherwise

• Apply the Cincinnati Prehospital Stroke Scale: Check for facial droop, arm drift (have patient hold both arms out), and speech abnormalities 4, 3
• The combination of left arm numbness with facial weakness or speech disturbance has a 72% probability of stroke 3
• Isolated numbness alone (hemibody sensory loss) still represents high risk for stroke 1

Timing Determines Urgency Level

Within 48 Hours of Symptom Onset (HIGHEST RISK)

Patients presenting within 48 hours with unilateral numbness are at HIGH RISK for recurrent stroke and require same-day assessment at the closest stroke prevention clinic or emergency department with advanced stroke capacity. 1

• 10% risk of completed stroke within the first week, with highest risk in the first 48 hours 3, 5
• These patients should receive comprehensive clinical evaluation and investigations by a healthcare professional with stroke expertise within 24 hours of first contact 1

Between 48 Hours and Two Weeks (INCREASED RISK)

• Patients remain at increased risk of recurrent stroke 1
• Should receive comprehensive evaluation by stroke specialist within 24 hours 1

Beyond Two Weeks (LOWER RISK)

• May be seen by neurologist or stroke specialist within one month 1
• However, do not assume "atypical" sensory symptoms are benign—recent population-based data shows non-consensus TIA symptoms (including isolated sensory loss) carry 90-day stroke risk of 10.6%, similar to classic TIA 5

Immediate Actions (Call 9-1-1)

Do not wait to see if symptoms resolve—call emergency services immediately. 1, 3

• Only 44% of TIA patients seek medical attention within hours, yet early stroke risk is highest in the first 48 hours 6
• Many patients incorrectly assume transient symptoms are not serious—this is a dangerous misconception 6, 5

While awaiting EMS:

• Check blood glucose immediately—hypoglycemia can mimic stroke 3
• Note exact time of symptom onset or last known normal time—this determines treatment eligibility 3
• Keep the affected arm at heart level (if arterial occlusion suspected, do NOT elevate) 2

Emergency Department Evaluation

Immediate Imaging (Within 10 Minutes of Arrival)

Brain imaging must be performed immediately to differentiate ischemic from hemorrhagic stroke, as this fundamentally changes treatment. 1, 4, 3

• MRI with diffusion-weighted imaging is preferred to detect acute ischemic changes 4
• CT head without contrast if MRI unavailable to rule out hemorrhage 4
• CT angiography or MR angiography from aortic arch to vertex to evaluate carotid and vertebral artery disease 1, 4
  • This "arch-to-vertex" imaging identifies carotid stenosis requiring urgent revascularization 1
  • Extracranial carotid stenosis >50% may require carotid endarterectomy 1

If Arterial Occlusion Suspected

• CT angiography from aortic arch to fingertips identifies occlusion location and differentiates thrombosis from dissection 2
• Initiate anticoagulation (heparin bolus followed by infusion) unless contraindicated, to prevent thrombus propagation 2
• Endovascular thrombectomy/thrombolysis for acute thromboembolism 2

Laboratory Investigations

The following tests should be obtained routinely: 1

• Complete blood count 1
• Electrolytes, renal function (creatinine, eGFR) 1
• Coagulation studies (aPTT, INR) 1
• Capillary glucose level 1
• Electrocardiogram to assess for atrial fibrillation or acute cardiac event 1, 3

Treatment Based on Diagnosis

If TIA/Minor Stroke Confirmed

Dual antiplatelet therapy (aspirin + clopidogrel 75 mg) is recommended for the first 21 days or longer in patients with symptomatic carotid stenosis not undergoing revascularization, followed by long-term single antiplatelet therapy. 1

• This reduces stroke risk in the critical early period 1
• Carotid ultrasound should be performed to identify extracranial carotid stenosis >70% requiring carotid endarterectomy 1

If Acute Arterial Occlusion Confirmed

• Outcome depends entirely on time to reperfusion 2
• Vascular surgery consultation for thrombectomy/embolectomy 2
• Monitor for compartment syndrome post-revascularization and treat with fasciotomy if needed 1, 2

Common Pitfalls to Avoid

Do not dismiss isolated sensory symptoms as "atypical" or low-risk. Population-based data demonstrates that non-consensus TIA symptoms (including isolated numbness) carry a 90-day stroke risk of 10.6%, nearly identical to classic TIA (11.6%). 5

Do not wait for symptoms to resolve before seeking care. Patients with non-consensus TIA are less likely to seek same-day medical attention (59% vs 75% for classic TIA), yet they have an 8% rate of recurrent stroke before seeking attention. 5

Do not assume weekend timing justifies delay. Studies show greater delays when TIA occurs on weekends, but stroke risk is time-dependent regardless of day of week. 6

Do not forget to check for pulse and blood pressure asymmetry. The combination of unilateral numbness with absent pulse indicates acute arterial occlusion, not stroke, requiring completely different management. 2