From Progressive bulbar palsy (PBP)

Progressive bulbar palsy, also called progressive bulbar atrophy, involves the brain stem—the bulb-shaped region containing lower motor neurons needed for swallowing, speaking, chewing, and other functions. Symptoms include pharyngeal muscle weakness (involved with swallowing), weak jaw and facial muscles, progressive loss of speech, and tongue muscle atrophy. Limb weakness with both lower and upper motor neuron signs is almost always evident but less prominent. Individuals are at increased risk of choking and aspiration pneumonia, which is caused by the passage of liquids and food through the vocal folds and into the lower airways and lungs. Affected persons have outbursts of laughing or crying (called emotional lability). Stroke and myasthenia gravis may have certain symptoms that are similar to those of progressive bulbar palsy and must be ruled out prior to diagnosing this disorder. In about 25 percent of individuals with ALS, early symptoms begin with bulbar involvement. Some 75 percent of individuals with classic ALS eventually show some bulbar involvement. Many clinicians believe that progressive bulbar palsy by itself, without evidence of abnormalities in the arms or legs, is extremely rare.

From NIH Motor Neuron Diseases Fact Sheet