What are the implications and necessary actions for unilateral facial weakness with preserved forehead wrinkling, suggesting a possible stroke?

Unilateral Facial Weakness with Preserved Forehead Wrinkling: Central Lesion Until Proven Otherwise

This presentation indicates a central (upper motor neuron) lesion affecting the facial nerve pathway above the facial nucleus, most commonly from an acute ischemic stroke, and requires immediate emergency department evaluation with brain imaging within 24 hours. 1

Critical Distinction: Central vs. Peripheral Facial Weakness

The ability to wrinkle the forehead distinguishes central from peripheral facial nerve lesions:

• Central lesions (stroke): Forehead muscles are spared due to bilateral cortical innervation of the upper facial muscles. Only the lower face (mouth, cheek) shows weakness. 2
• Peripheral lesions (Bell's palsy): Both upper and lower facial muscles are affected equally, with inability to wrinkle forehead or close the eye. 3

Your patient's preserved forehead wrinkling strongly suggests stroke rather than Bell's palsy. 2

Immediate Risk Stratification and Actions

VERY HIGH Risk Category (Within 48 Hours of Symptom Onset)

Patients presenting within 48 hours with unilateral facial weakness are at VERY HIGH risk for stroke, with up to 10% risk of recurrent stroke within the first week. 1, 4

Required immediate actions:

• Send immediately to an emergency department with advanced stroke care capabilities (on-site brain imaging and access to acute stroke treatments). 1
• Urgent brain imaging (CT or MRI) must be completed as soon as possible within 24 hours to differentiate ischemic from hemorrhagic stroke. 1, 2
• Non-invasive vascular imaging (CTA or MRA from aortic arch to vertex) should be performed within 24 hours to identify carotid stenosis or intracranial occlusion. 1
• 12-lead ECG without delay to assess for atrial fibrillation or acute cardiac events. 1
• Bedside glucose testing immediately to rule out hypoglycemia as a stroke mimic. 2

HIGH Risk Category (48 Hours to 2 Weeks)

Patients presenting between 48 hours and 2 weeks with unilateral facial weakness require comprehensive clinical evaluation by a healthcare professional with stroke expertise, ideally within 24 hours of first contact. 1

Critical Diagnostic Pitfalls to Avoid

Do Not Assume Bell's Palsy Based on Isolated Facial Weakness

Rare but documented cases of pontine or pontomedullary junction strokes can present with isolated upper and lower facial weakness mimicking Bell's palsy. 5, 6, 7 However, these typically involve the facial nerve fascicles within the brainstem and would affect both upper and lower face equally.

Red flags that mandate brain imaging even with complete facial involvement:

• Associated diplopia, vertigo, or dysphagia 7
• Contralateral motor or sensory deficits 7
• Gaze palsy or nystagmus 7
• Ataxia or dysarthria 1
• Fluctuating symptoms 1

Do Not Delay Imaging for Laboratory Results

Brain imaging takes absolute priority over all other testing. Thrombolytic therapy should not be delayed while waiting for laboratory results unless there is clinical suspicion of bleeding abnormality, thrombocytopenia, or anticoagulant use. 1

Essential Laboratory and Imaging Workup

Complete within 24 hours:

• CT or MRI brain (urgent, within hours if possible) 1, 2
• CTA or MRA from aortic arch to vertex 1
• 12-lead ECG 1
• Complete blood count 2
• Serum electrolytes and creatinine 2
• Fasting blood glucose 2
• Coagulation studies if anticoagulation suspected 1

Additional cardiac evaluation if cardioembolic source suspected:

• Extended cardiac monitoring for paroxysmal atrial fibrillation 4
• Echocardiography (transthoracic or transesophageal) 4

Blood Pressure Management Considerations

Do not treat elevated blood pressure acutely unless:

• Diastolic BP >120 mmHg or systolic BP >220 mmHg in non-thrombolytic candidates 1
• Systolic BP >185 mmHg or diastolic BP >110 mmHg if thrombolytic therapy is being considered 1

Transient hypertension represents the body's compensatory response to maintain cerebral perfusion and should generally not be treated in the hyperacute phase. 1

Neurological Assessment

Use the National Institutes of Health Stroke Scale (NIHSS) to quantify stroke severity and track neurological changes over time. This is the most widely used and validated stroke deficit scale among stroke neurologists. 1

Most Likely Vascular Territory

Middle cerebral artery (MCA) territory stroke is most likely when facial weakness occurs with arm weakness or speech disturbance. 2 Patients with large MCA infarctions may develop malignant cerebral edema requiring decompressive hemicraniectomy, especially in patients under 60 years. 2