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Pseudobulbar palsy is caused by bilateral corticobulbar tract disease (UMN
disease). The patient will have upper motor neuron signs including a positive
jaw jerk and slow side-to-side tongue movements with the jaw frequently
moving with the tongue. The patient has incomplete elevation of the palate
with excessive nasal air escape when saying "pah" or "kah" (decreased
volitional activity of CN 9 & 10) but a hyperactive gag reflex (increased
non-voluntary or reflex motor action of CN 9 & 10).
When a patient has weakness of the palatal muscles it is important to determine
if this is from UMN vs. LMN disease. Patients with bilateral LMN lesions
have both absent voluntary and reflex activity. Patients with bilateral
UMN weakness or dysfunction will lack voluntary movement of the palate but
will have a hyperactive gag reflex (just like a hyperactive DTR with UMN
disease). For UMN disease to cause palatal weakness it must be bilateral
because there is bilateral UMN innervation for the nucleus ambiguus.