What are the causes of bulbar palsy?

Causes of Bulbar Palsy

Bulbar palsy results from lower motor neuron degeneration affecting the motor nuclei in the medulla and pons, most commonly due to amyotrophic lateral sclerosis (ALS), but also caused by vascular, infectious, inflammatory, neoplastic, and immune-mediated processes affecting the brainstem motor nuclei.

Primary Neurodegenerative Causes

Amyotrophic Lateral Sclerosis (ALS)

• ALS is the most common cause of bulbar palsy, characterized by progressive degeneration of motor neurons in the brainstem and spinal cord 1
• Bulbar-onset ALS accounts for approximately one-third of ALS cases, with patients presenting initially with dysarthria and dysphagia 1
• The disease reflects degeneration of motor neurons in the primary motor cortex, corticospinal tracts, brainstem, and spinal cord 1
• Progressive bulbar palsy (PBP) represents a classic phenotype with more rapid progression, while isolated bulbar palsy (IBP) progresses more slowly with relatively benign prognosis 2
• Sporadic ALS accounts for 90-95% of cases, while 5-10% are familial with identified genetic mutations including SOD1 (20% of familial cases) and TARDBP genes (2-5% of familial cases) 1

Motor Neuron Disease Variants

• Progressive bulbar palsy specifically involves degeneration of motor nuclei in the medulla, producing atrophy and fasciculations of tongue musculature 3
• The pathological mechanism involves loss of motor neurons with intraneuronal ubiquitin-immunoreactive inclusions in upper motor neurons and TDP-43 immunoreactive inclusions in degenerating lower motor neurons 1

Vascular Causes

Brainstem Stroke

• Brainstem infarction affecting the pons can damage facial nerve nuclei and other motor nuclei, resulting in bulbar symptoms 4
• Posterior circulation strokes may present with acute onset bulbar dysfunction 4
• Vascular lesions within the brainstem can affect multiple cranial nerve nuclei simultaneously 4

Infectious and Inflammatory Causes

Infectious Meningitis

• Tuberculous, fungal, and Lyme disease meningitis can affect cranial nerves in the basilar subarachnoid space, causing multiple cranial nerve palsies including bulbar involvement 4
• Infectious processes may cause inflammation of cranial nerves and their nuclei within the brainstem 4

Immune-Mediated Inflammatory Causes

• Immune checkpoint inhibitor (ICI)-induced myositis occurs in approximately 1% of patients receiving cancer immunotherapy, with median onset at 4 weeks of treatment, presenting with bulbar and oculomotor weakness 5
• The pathological mechanism involves rhabdomyolysis with elevated muscle enzymes, spontaneous EMG activity, and myogenic recruitment patterns 5
• This condition carries approximately 20% mortality rate when bulbar involvement is present, compared to less than 10% for idiopathic inflammatory myositis 5

Demyelinating Disease

• Multiple sclerosis can affect brainstem structures, causing demyelinating plaques that damage motor nuclei 4
• Demyelinating lesions are a primary consideration in younger patients presenting with brainstem symptoms 4

Neoplastic Causes

Primary Brain Tumors

• Brainstem tumors can directly compress or infiltrate motor nuclei in the pons and medulla 4
• Intrinsic brainstem gliomas may present with progressive bulbar symptoms 4

Metastatic Disease and Perineural Spread

• Perineural or leptomeningeal tumor spread can affect cranial nerves in the subarachnoid space 4
• Sarcoid and neoplastic infiltration of the basilar subarachnoid space may cause multiple cranial nerve palsies 4

Skull Base Tumors

• Meningiomas, schwannomas, and paragangliomas affecting the skull base can compress cranial nerves 4
• Cholesteatomas and epidermoid cysts may cause cranial nerve dysfunction 4

Traumatic Causes

Direct Brainstem Injury

• Traumatic injury to the brainstem can damage motor nuclei directly 4
• Temporal bone fractures may affect the facial nerve course through the temporal bone 4

Granulomatous Causes

Sarcoidosis

• Neurosarcoidosis can cause granulomatous inflammation affecting cranial nerves and brainstem structures 4
• Sarcoid may present with multiple cranial nerve palsies through basilar subarachnoid space involvement 4

Vascular Compression

Aneurysms and Vascular Malformations

• Vascular compression from adjacent aneurysms can cause cranial nerve palsies 4
• Vascular malformations within the brainstem may compress motor nuclei 4

Rheumatological Causes

Systemic Autoimmune Disease

• Systemic lupus erythematosus (SLE) can cause velopharyngeal insufficiency through dysmotility of velopharyngeal structures 5
• Sjögren syndrome may present with dry mouth and, rarely, neurological manifestations, though bulbar palsy is uncommon 5

Guillain-Barré Syndrome Variants

• Certain GBS variants can present with bulbar weakness combined with cranial symptoms or ataxia 5

Critical Diagnostic Considerations

The pattern of motor neuron involvement distinguishes true bulbar palsy (lower motor neuron) from pseudobulbar palsy (upper motor neuron):

• Bulbar palsy shows pure lower motor neuron signs with atrophy, fasciculations, and absent reflexes 2, 3
• The presence of upper motor neuron limb signs alongside bulbar symptoms suggests ALS rather than isolated bulbar palsy 2
• Isolated bulbar palsy (IBP) is characterized by pure lower motor neuron bulbar signs, older onset age (mean 58.5 years), female predominance, and better prognosis (mean survival 40.5 months) compared to progressive bulbar palsy 2

Key diagnostic pitfall: Immune-related myositis requires high clinical suspicion early in immunotherapy treatment (median 4 weeks exposure), as delayed recognition with bulbar involvement carries significant mortality risk 5