What are the differential diagnoses and initial management for a unilateral facial droop that includes the eyebrow (upper facial muscle weakness)?

Differential Diagnoses for Unilateral Facial Droop with Eyebrow Involvement

When facial droop includes the eyebrow and forehead muscles, this indicates a lower motor neuron (peripheral) lesion affecting the facial nerve (CN VII) anywhere from the brainstem nucleus through its extracranial course—this is fundamentally different from stroke, which typically spares the forehead. 1, 2

Critical Anatomic Distinction

• Peripheral (lower motor neuron) facial palsy affects the entire ipsilateral face including forehead muscles, distinguishing it from central causes like stroke where forehead function is preserved due to bilateral cortical innervation 1, 2
• The facial nerve can be damaged at multiple points: within the pons, cerebellopontine angle, internal auditory canal, temporal bone, or extracranially 1

Primary Differential Diagnoses

Bell's Palsy (Most Common - 70% of Cases)

• Acute onset (<72 hours) of unilateral facial paralysis without identifiable cause, attributed to inflammation and edema of the facial nerve within the temporal bone canal 1, 2
• Patients typically experience complete recovery by 6 months, hastened with corticosteroids 1
• May present with facial droop, pain around jaw/ear, hyperacusis, reduced taste, and decreased lacrimation 1

Infectious Causes

• Lyme disease accounts for up to 25% of facial paralysis in endemic areas and is often bilateral—check Lyme serology in appropriate geographic contexts 3, 2
• Ramsay Hunt syndrome (herpes zoster oticus) presents with vesicular rash in the ear canal and has worse prognosis than Bell's palsy, requiring antiviral therapy plus corticosteroids 2
• Mastoiditis or parotiditis can cause facial nerve involvement with associated swelling and infection signs 2

Traumatic Causes

• Temporal bone fractures from head trauma can cause immediate or delayed facial nerve paralysis (delayed presentation may occur up to 3 days post-injury) 1, 4
• Iatrogenic injury from TMJ surgery or other facial procedures accounts for 40% of surgical facial nerve injuries 1

Neoplastic Causes

• Gradual progression over days to weeks suggests tumor rather than Bell's palsy 2
• Parotid tumors, facial/vestibular schwannomas, meningiomas, cholesteatomas, and perineural tumor spread can all affect the facial nerve 1
• Brain tumors may cause facial weakness with additional neurologic symptoms 2

Brainstem Pathology

• Pontine infarction, vascular malformations, multiple sclerosis, or tumors affecting the facial nucleus 1
• Brainstem lesions are typically accompanied by additional neurologic symptoms (diplopia, dysphagia, dizziness, other cranial nerve deficits) that help localize the lesion 1, 5
• Rarely, isolated brainstem or cortical infarct can present as isolated facial palsy 1

Systemic/Inflammatory Diseases

• Sarcoidosis causes granulomatous inflammation of the facial nerve 2
• Guillain-Barré syndrome presents with bilateral facial weakness and ascending paralysis 2

Neuromuscular Junction Disorders

• Myasthenia gravis can present as persistent unilateral ptosis with ipsilateral facial droop without the typical fluctuating weakness pattern 6
• Consider acetylcholine receptor antibody testing when presentation is atypical 6

Initial Management Algorithm

Immediate Clinical Assessment

• Document onset timing: acute (<72 hours) suggests Bell's palsy or stroke; gradual suggests neoplasm 3, 2
• Confirm forehead involvement to establish peripheral pattern 1, 2
• Examine for vesicular rash in ear canal (Ramsay Hunt syndrome) 2
• Assess for facial swelling/redness, which is atypical for Bell's palsy and suggests infection 2
• Check for additional cranial nerve deficits, which indicate brainstem pathology 1, 5
• Inquire about head trauma history, including delayed presentations 4

Imaging Strategy

• MRI brain with contrast is the essential first-line imaging study to evaluate the facial nerve pathway from brainstem to peripheral branches 1, 5, 3
• High-resolution temporal bone CT is complementary to MRI for characterizing osseous integrity, fractures, and bony facial nerve canal involvement 1
• Do NOT use routine CT head alone or CTA head as isolated studies—they lack sufficient detail for facial nerve evaluation 1

Laboratory Testing (Selective)

• Lyme serology only in endemic areas with appropriate exposure history 5, 3, 2
• ESR/CRP if age >50 with temporal headache or jaw claudication (giant cell arteritis) 5, 3
• Acetylcholine receptor antibodies if presentation suggests myasthenia gravis 6

Treatment Initiation

• For presumed Bell's palsy: prescribe oral corticosteroids within 72 hours of onset (prednisolone 50 mg daily for 10 days OR prednisone 60 mg daily for 5 days with 5-day taper), with evidence showing 83% recovery at 3 months versus 63.6% with placebo 3, 2
• For Ramsay Hunt syndrome: antiviral therapy PLUS corticosteroids 2
• For Lyme disease: parenteral ceftriaxone for 14-21 days; steroids may be added after antimicrobial initiation 2
• Never give steroids alone for infection-related facial palsy—first treat underlying infection with appropriate antimicrobials 2

Red Flags Requiring Urgent Workup

• Progressive or persistent symptoms beyond 2-4 months warrant imaging even if initially thought to be Bell's palsy 1
• Bilateral facial weakness is never idiopathic—investigate for Lyme disease, sarcoidosis, or Guillain-Barré syndrome 2
• Additional neurologic symptoms (dizziness, dysphagia, diplopia) suggest brainstem pathology 1, 5
• Facial swelling and redness with facial palsy is atypical for Bell's palsy and mandates investigation for infectious causes 2

Common Pitfalls to Avoid

• Do not assume all acute facial weakness is Bell's palsy—30% have identifiable causes requiring different management 2
• Do not image typical Bell's palsy presentations routinely, but atypical features (recurrent, persistent >2-4 months, bilateral, with swelling/redness) require MRI 1, 2
• Do not miss delayed traumatic facial nerve paralysis, which can present up to 3 days after head injury 4
• Do not overlook myasthenia gravis, which may present without typical fluctuating weakness 6