What is the differential diagnosis for a patient with left-sided facial nerve palsy of the Lower Motor Neuron (LMN) type and tongue deviation to the left?

Differential Diagnosis: Left LMN Facial Palsy with Ipsilateral Tongue Deviation

The combination of left-sided lower motor neuron facial palsy with ipsilateral tongue deviation to the left indicates involvement of both cranial nerves VII and XII on the same side, pointing to a lesion affecting the lower brainstem (medulla), skull base, or extracranial course where these nerves travel in proximity—most commonly neoplasm, vascular lesions, or inflammatory processes affecting the jugular foramen/hypoglossal canal region. 1

Key Anatomical Localization

The simultaneous involvement of CN VII (facial nerve) and CN XII (hypoglossal nerve) on the same side narrows the differential significantly:

• Tongue deviation occurs toward the side of the lesion in LMN hypoglossal nerve palsy, indicating left-sided CN XII involvement 1
• LMN facial palsy affects the entire ipsilateral face including the forehead, distinguishing it from supranuclear lesions 1
• These nerves can be affected together at the brainstem (medulla), skull base (jugular foramen/hypoglossal canal region), or extracranial carotid space 1

Primary Differential Diagnoses

Neoplastic Causes (Most Common for Combined CN Palsies)

• Skull base tumors are the most common cause of isolated hypoglossal nerve palsy, particularly neoplasms involving the hypoglossal canal 1
• Malignant tumors in the carotid space can affect both CN VII extracranially and CN XII as they course through this region 1
• Jugular foramen tumors (paragangliomas, schwannomas, meningiomas) can involve multiple lower cranial nerves including CN VII and XII 1
• Metastatic disease to the skull base should be considered, especially with known primary malignancy 1

Vascular Causes

• Internal carotid artery dissection can result in isolated CN XII palsy or multiple variable patterns of cranial nerve palsies including CN VII and XII 1
• Brainstem infarction (medullary stroke) affecting the facial nerve nucleus/fascicles and hypoglossal nucleus can present with ipsilateral LMN facial palsy and tongue deviation, though typically accompanied by other brainstem signs 1, 2
• Nuclear lesions in the brainstem are usually accompanied by additional neurologic deficits beyond isolated cranial neuropathies 1

Inflammatory/Infectious Causes

• Inflammatory processes affecting the skull base or carotid space can involve multiple cranial nerves 1
• Infectious processes including bacterial meningitis, syphilis, or HIV-related complications may cause multiple cranial neuropathies 1
• Lyme disease should be considered in endemic areas, particularly with multiple cranial nerve involvement 1
• Sarcoidosis can cause multiple cranial neuropathies 1

Traumatic Causes

• Skull base fractures involving the temporal bone and hypoglossal canal from trauma 1
• Surgical injury from prior neck or skull base surgery affecting both nerve pathways 1

Demyelinating Disease

• Multiple sclerosis can cause brainstem lesions affecting multiple cranial nerve nuclei, though typically with other CNS manifestations 1

Critical Diagnostic Approach

Immediate Imaging Required

MRI of the head, orbit, face, and neck with and without contrast is the preferred imaging modality for evaluating combined cranial neuropathies 1, 3

• MRI directly images the entire course of both CN VII and CN XII from brainstem through skull base to extracranial segments 1
• Contrast-enhanced sequences are essential to identify tumors, inflammation, or vascular lesions 1
• High-resolution CT of the temporal bone and skull base provides complementary information about osseous integrity of the hypoglossal canal and temporal bone 1

Clinical Red Flags

This presentation is NOT typical Bell's palsy, which is isolated CN VII involvement without other cranial nerve deficits 1, 3:

• Multiple cranial nerve involvement mandates imaging regardless of symptom duration 1, 3
• Do not delay imaging to observe for spontaneous recovery 1, 3
• Bilateral facial palsy or involvement of other cranial nerves is atypical and warrants extensive workup 1, 3

Additional Workup Considerations

• Lyme serology if in endemic area or with appropriate exposure history 1
• Consider lumbar puncture for CSF analysis if infectious/inflammatory etiology suspected 4
• Vascular imaging (CTA or MRA) if carotid dissection suspected, particularly with acute onset 1

Common Pitfalls to Avoid

• Do not assume isolated Bell's palsy when multiple cranial nerves are involved—this requires immediate imaging 1, 3
• Do not miss carotid dissection in acute presentations, which can cause multiple lower cranial nerve palsies 1
• Nuclear brainstem lesions typically present with additional neurologic deficits beyond isolated cranial neuropathies; their absence suggests skull base or extracranial pathology 1
• Hypoglossal nerve palsy accompanied by other lower cranial nerve palsies (CN IX, X, XI, XII) suggests jugular foramen or brainstem pathology 1