What are the causes of lower motor neuron (LMN) facial palsy in a young adult male with severe hypertension?

Causes of Lower Motor Neuron Facial Palsy

Lower motor neuron (LMN) facial palsy results from pathology affecting the facial nerve nucleus in the pons or any portion of the facial nerve along its course through the cerebellopontine angle, internal auditory canal, temporal bone, or extracranial segments, with Bell's palsy being the most common cause but requiring exclusion of secondary etiologies—particularly in the context of severe hypertension. 1

Primary Causes by Anatomical Location

Brainstem/Nuclear Lesions

• Pontine infarction affecting the facial nerve nucleus, often accompanied by additional neurologic findings such as ipsilateral sixth nerve palsy (the seventh nerve curves over the sixth nerve nucleus) or contralateral hemiparesis from corticospinal tract involvement 1, 2
• Vascular malformations, tumors, or demyelinating disease (multiple sclerosis) within the pons 1
• Facial colliculus syndrome causing LMN facial palsy with conjugate gaze palsy and cerebellar signs, even in young patients without traditional vascular risk factors 2

Cerebellopontine Angle and Internal Auditory Canal

• Vestibular schwannomas (acoustic neuromas) and facial schwannomas 1
• Meningiomas compressing the facial nerve 1
• Epidermoid cysts within the cerebellopontine angle 1

Temporal Bone Segment

• Cholesteatomas eroding through the temporal bone 1
• Temporal bone trauma affecting the labyrinthine, tympanic, or mastoid segments 1
• Intrinsic bone tumors involving the temporal bone 1

Extracranial Causes

• Parotid tumors affecting the facial nerve as it courses through the parotid gland 1
• Perineural tumor spread from head and neck malignancies 1
• Inflammatory conditions affecting the extracranial facial nerve 1

Bell's Palsy (Idiopathic Facial Palsy)

Bell's palsy is strictly a diagnosis of exclusion requiring acute onset (within 72 hours) of unilateral facial paresis or paralysis without identifiable cause. 1, 3

• Viral etiology suspected (particularly herpes simplex virus) causing facial nerve inflammation and edema within the narrow temporal bone canal 1
• Most common cause of acute peripheral facial nerve palsy, with approximately 70% of patients with complete paralysis recovering fully within 6 months and up to 94% with incomplete paralysis 1
• Should NOT be diagnosed when facial palsy occurs in the context of other conditions such as migraine, as Bell's palsy requires no identifiable cause 3

Hypertension-Associated Facial Palsy

In the context of severe hypertension, peripheral facial nerve palsy represents a recognized but underappreciated complication, particularly in children and young adults. 4, 5

Pathophysiology and Clinical Features

• Severe systemic hypertension (often >180/120 mmHg) can cause peripheral facial palsy through microvascular damage and nerve ischemia 4, 5
• Predominantly affects children (23 of 26 cases in systematic review were pediatric), though adult cases occur 5
• Unilateral in most cases (25/26), with recurrence in approximately one-third of patients 5
• Substantial diagnostic delay common, with median 45 days between facial symptoms and hypertension diagnosis (range 0 days to 2 years) 5
• Incidence of 4.8% among children with severe hypertensive complications in case series 5

Hypertensive Emergency Context

• Drug-induced hypertension (atomoxetine, sympathomimetics, cocaine, NSAIDs, steroids) can precipitate facial palsy 4, 1
• Secondary hypertension found in 20-40% of patients with malignant hypertension, requiring screening for renal artery stenosis, pheochromocytoma, or primary aldosteronism 1, 6
• Favorable outcome with adequate antihypertensive treatment, though pathophysiology remains debated 5

Infectious and Inflammatory Causes

• Herpes simplex virus and herpes zoster (Ramsay Hunt syndrome) causing facial nerve inflammation 1
• Lyme disease (Borrelia burgdorferi) in endemic areas 1
• Sarcoidosis causing granulomatous inflammation of the facial nerve 3
• Miller Fisher syndrome (Guillain-Barré variant) with anti-GM1 antibodies, potentially presenting with delayed bilateral facial palsy 7

Vascular Causes

• Lateral medullary syndrome with aberrant supranuclear facial nerve fiber involvement, though typically presents as UMN pattern 8
• Hemifacial spasm from vascular compression of the facial nerve at the root exit zone (distinct from palsy but related vascular pathology) 1

Clinical Evaluation Algorithm

Immediate Assessment

1. Confirm LMN pattern: Complete ipsilateral facial paralysis including forehead involvement (distinguishes from UMN/stroke pattern which spares forehead) 1, 3
2. Measure blood pressure: Document severe elevation (>180/120 mmHg) and assess for hypertensive emergency with target organ damage 1, 6
3. Screen for additional neurologic findings: Other cranial nerve palsies, cerebellar signs, gaze abnormalities, or pyramidal tract signs exclude idiopathic Bell's palsy 1, 3, 2

Diagnostic Workup

• MRI brain with and without contrast indicated for atypical presentations, symptoms persisting >2-4 months, recurrent episodes, or presence of other neurologic findings 1, 3
• High-resolution temporal bone CT provides complementary osseous imaging when temporal bone pathology suspected 1
• Laboratory evaluation in hypertensive patients: CBC, creatinine, electrolytes, LDH, haptoglobin, urinalysis to assess for thrombotic microangiopathy and target organ damage 1, 6
• Fundoscopy essential to identify malignant hypertensive retinopathy (bilateral hemorrhages, cotton wool spots, papilledema) 6

Red Flags Requiring Urgent Imaging

• Recurrent episodes on the same side warrant workup for structural lesions, sarcoidosis, or other underlying pathology 3
• Additional neurologic symptoms (diplopia, other cranial nerve involvement, ataxia) exclude idiopathic Bell's palsy 3, 2
• Young patients without vascular risk factors presenting with LMN facial palsy and other neurologic signs require stroke evaluation 2
• Severe hypertension (>180/120 mmHg) with facial palsy, particularly in children or with delayed diagnosis 4, 5

Management Considerations

Acute Treatment

• Corticosteroids within 72 hours may hasten recovery in Bell's palsy, though evidence specific to hypertension-associated cases is limited 1, 3
• Mandatory eye protection: Lubricating drops, ointments, and nighttime taping to prevent corneal damage from incomplete eyelid closure 3
• Blood pressure management in hypertensive emergency: ICU admission with IV antihypertensives (nicardipine, labetalol) targeting 20-25% MAP reduction in first hour 1, 6

Follow-up Protocol

• Reassess at 3 months if facial recovery incomplete; refer to facial nerve specialist for persistent weakness 3
• Screen for secondary hypertension after stabilization in patients with severe hypertension and facial palsy 1, 6, 5
• Monitor for recurrence and development of new neurologic symptoms requiring urgent evaluation 3