GENERAL NEUROLOGY

Bulbar and pseudobulbar palsy

David Goldemund M.D.
Updated on 13/07/2024, published on 04/02/2024

Jaw reflex

  • the jaw reflex (jaw-jerk or masseter reflex) is a deep tendon reflex that involves the muscles of mastication, primarily the masseter muscle
  • anatomy (trigemino-trigeminal reflex):
    • sensory component: trigeminal nerve (CN V/3)
    • motor component: trigeminal nerve (CN V/3)
    • muscle tested: masseter
  • testing: with the patient’s jaw slightly open, the reflex is elicited by tapping with a reflex hammer on the chin or on a tongue blade resting on the lower teeth
  • the normal response: sudden stretching of the masseter muscle leads to its reflex contraction ⇒ the jaw moves upward
  • abnormal responses:
    • the reflex is extinguished in a primary pontine lesion or as a consequence of central rostrocaudal deterioration syndrome reaching the level of the upper pons (transsection)
    • the reflex ceases in a deep coma due to muscular atonia
    • an exaggerated jaw jerk (sometimes with clonus) implies a bilateral upper motor neuron lesion (e.g., in pseudobulbar palsy)

Gag reflex

  • the gag reflex (pharyngeal reflex) is a protective mechanism that helps prevent foreign objects from entering the throat
  • anatomy involved:
    • sensory component: glossopharyngeal nerve (CN IX) and vagus nerve (CN X)
    • motor component: vagus nerve (CN X)
    • muscles: pharyngeal constrictors and levator veli palatini
  • the examiner touches the posterior pharyngeal wall, tonsillar area, or base of the tongue with a tongue depressor or cotton-tipped applicator
  • normal response involves contraction of the pharyngeal muscles, elevation of the soft palate, and retching or gagging sensation
    • some individuals may have a very sensitive reflex, while others may have a diminished or absent reflex without any underlying pathology
  • absent or diminished gag reflex may indicate:
    • damage to CN IX or CN X
    • pseudobulbar palsy
    • brainstem lesions

Bulbar palsy

  • motor disorder, resulting from lesions of CN IX, X, XI (lateral system) and CN XII or their nuclei

Clinical Presentation

  • articulation impairment ranging from slurred speech (dysarthria) to complete loss of articulation (anarthria)
  • dysphonia
  • dysphagia (liquids leaking through the nose when drinking, increased risk of aspiration)
  • drooping soft palate
  • atrophy and fasciculation of the tongue  Atrophic tongue in bulbar syndrome due to ALS (Toro, 2014)
  • reduced or absent gag reflex
  • decreased jaw reflex
  • expansive processes may affect brainstem centers that control breathing, heart function, and vasomotor activity

Etiology

  • neurodegenerative diseases
    • progressive bulbar palsy (Duchenne)
    • amyotrophic lateral sclerosis (ALS)
    • syringomyelia
    • Kennedy’s disease (bulbospinal muscular atrophy) – bulbar syndrome, gynecomastia, hand tremor, muscle pains, and cramps
  • lesional disorders of the brainstem or cranial nerves
    • infections (viral encephalitis)
    • multiple sclerosis
    • polyradiculoneuritis (especially the Miller-Fisher variant)
    • ischemia → vertebrobasilar stroke
    • tumors
      • brainstem gliomas
      • meningiomas affecting the lower cranial nerves
      • metastatic lesions
  • autoimmune disorders
    • myasthenia gravis (can present with bulbar symptoms)
    • sarcoidosis affecting the brainstem

Pseudobulbar palsy

  • it results from bilateral involvement of the central motor pathways of the cranial nerves (corticobulbar tract)
    • unilateral lesions of the corticobulbar tract typically do not lead to significant impairment of cranial nerve function, as supranuclear innervation is both ipsilateral and contralateral
    • a slight deviation of the tongue towards the side of limb paresis may be observed due to the dominance of the contralateral healthy genioglossus muscle
    • mild dysarthria may be present, often due to paresis of CN VII (facial nerve), but swallowing is generally unaffected

Clinical Presentation

  • motor dysfunction similar to that of bulbar palsy but without tongue atrophy and fibrillations
  • ↑↑ masseter reflex (potentially presenting with clonus)
  • markedly positive axial signs
  • pseudobulbar affect (PBA), also known as emotional incontinence, characterized by sudden and unpredictable episodes of involuntary crying or laughing that are often inappropriate to the social context   (Ahmed, 2013)
    • PSA is caused by a disconnection between the frontal lobe (which controls emotions) and the cerebellum and brainstem
  • monotonous or even aphonic speech
  • dysphagia
  • pyramidal or even extrapyramidal symptoms
    • “frontal gait” with bradybasia and brachybasia, resulting in postural instability and requiring assistance from another person to maintain balance

Etiology

  • cerebrovascular diseases
  • neurodegenerative disorders
    • initial stages of amyotrophic lateral sclerosis (ALS) before bulbar syndrome occurs
    • primary lateral sclerosis (PLS)
    • Progressive Supranuclear Palsy (PSP)
  • traumatic brain injury (bilateral or diffuse axonal injury)
  • genetic disorders
    • leukodystrophies
  • toxic-metabolic disorders
    • osmotic demyelination syndrome (central pontine myelinolysis)

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Bulbar and pseudobulbar palsy
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