What is the differential diagnosis for sudden onset facial and arm weakness?

Differential Diagnosis for Sudden Onset Facial and Arm Weakness

Acute ischemic stroke is the primary diagnosis that must be immediately considered and ruled out when a patient presents with sudden onset facial and arm weakness, as this combination has a 72% probability of stroke and requires emergent evaluation within minutes to hours to preserve brain tissue and prevent permanent disability or death. 1

Immediate Life-Threatening Diagnoses to Consider

Acute Ischemic Stroke (Most Common and Time-Critical)

• Middle cerebral artery (MCA) territory stroke is the most likely vascular territory when facial weakness, arm weakness, and speech disturbance occur together 2
• The combination of facial droop and arm weakness represents two of the three cardinal stroke signs in validated screening tools, with 88% of all strokes presenting with at least one of these features 1
• Patients presenting with unilateral weakness are at VERY HIGH risk for recurrent stroke, with up to 10% risk within the first week and highest risk in the first 48 hours 3

Hemorrhagic Stroke

• Intracerebral hemorrhage can present identically to ischemic stroke with facial and arm weakness 1
• Urgent brain imaging (CT or MRI) is required to differentiate ischemic from hemorrhagic stroke, as this distinction fundamentally changes treatment approach 3

Brainstem Stroke

• Pontine infarction can cause "uncrossed paralysis" presenting with contralateral facial palsy and limb weakness, mimicking higher cortical lesions 4
• Posterior circulation strokes may present with more subtle symptoms but carry similar risk for recurrent stroke 3

Other Neurological Emergencies

Guillain-Barré Syndrome (GBS)

• GBS can present with acute hemiparesis and cranial nerve palsy that mimics brainstem stroke, though this is rare 5
• Key distinguishing features include progression to bilateral symptoms, areflexia, and ascending pattern of weakness 5
• Cerebrospinal fluid analysis showing albuminocytologic dissociation and nerve conduction studies help differentiate GBS from stroke 5

Todd's Paralysis (Post-Ictal)

• Transient focal weakness following seizure activity can mimic stroke 1
• History of witnessed seizure activity and gradual resolution over hours helps distinguish this diagnosis 1

Hemiplegic Migraine

• Can present with unilateral weakness and facial symptoms 1
• Typically occurs in younger patients with history of similar episodes and gradual onset over minutes rather than sudden onset 1

Metabolic and Systemic Causes

Hypoglycemia

• Must be ruled out immediately as it can cause focal neurological deficits mimicking stroke 1
• Rapid bedside glucose testing is essential in all patients with acute weakness 3

Hyponatremia or Other Electrolyte Disturbances

• Severe electrolyte abnormalities can rarely cause focal neurological symptoms 3
• Basic laboratory investigations including serum electrolytes should be obtained 3

Critical Action Points

Immediate Assessment (Within Minutes)

• Activate emergency medical services (9-1-1) immediately - only 53% of stroke patients currently use EMS despite clear mortality benefit 1
• Apply validated stroke screening tools: Cincinnati Prehospital Stroke Scale (CPSS) has 59% sensitivity and 89% specificity for stroke when any single abnormality is present 1
• Establish exact time of symptom onset or last known normal time, as this determines treatment eligibility 1
• Check blood glucose immediately to rule out hypoglycemia 1

Emergency Department Evaluation (Within 60 Minutes)

• Urgent brain imaging (CT or MRI) must be completed without delay to differentiate ischemic from hemorrhagic stroke 3
• Non-invasive vascular imaging (CTA or MRA from aortic arch to vertex) should be performed within 24 hours 2, 3
• Electrocardiogram to assess for atrial fibrillation or acute cardiac event 3
• Complete blood count, serum electrolytes, creatinine, and fasting blood glucose 3

Common Pitfalls to Avoid

• Do not assume symptoms are "too mild" to be stroke - even transient symptoms carry 10% risk of completed stroke within one week 3
• Do not delay imaging for laboratory results - brain imaging takes priority over all other testing 3
• Patients and witnesses frequently fail to recognize stroke symptoms despite public education campaigns, with only 19.9% arriving within the 3-hour treatment window 6
• History of delaying medical care is a behavioral pattern associated with failure to activate emergency services for stroke symptoms 6

Special Considerations for MCA Territory Involvement

• Patients with large MCA infarctions may develop malignant cerebral edema requiring decompressive hemicraniectomy, especially in patients under 60 years 2
• Carotid imaging (ultrasound, CTA, or MRA) should be performed to assess for carotid stenosis requiring early revascularization 3
• Extended cardiac monitoring should be considered if paroxysmal atrial fibrillation is suspected as the embolic source 3