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Bulbar palsy is a syndrome that affects the brain’s lower motor neurons. There are several causes of bulbar palsy, including genetic, vascular, degenerative, and inflammatory diseases; malignancy; and bacterial toxins. It occurs when the brain’s lower cranial nerves are impaired because of trauma to the cells or motor control center of the brainstem, or from other lesions to the lower cranial nerves in the brainstem. “Bulbar” refers to the lower brainstem area, or medulla oblongata, which controls cranial nerves seven through 12, and “palsy” is a form of bodily weakness, so bulbar palsy is any weakness caused by lesion, trauma, or defect to these nerves or the area that controls them.
Genetic causes of bulbar palsy include Kennedy’s disease, which is a neuromuscular disorder, and acute intermittent porphyria, a metabolic disorder that can lead to neuron disease. A stroke that affects this lower area of the brainstem is called a “medullary infarction.” This damage to the vascular system can affect lower motor function of the lower cranial nerves. Motor neuron disease, which is caused by toxins; and other degenerative diseases, including syringobulbia, which is a complication in neurological pathways that causes dilation in the inner part of the brain; can also cause bulbar palsy.
Lower motor neurons may be damaged by infection leading to inflammation, as in the cases of Guillan-Barré syndrome, poliomyelitis, and Lyme disease, and in the case of a brain tumor. Guillan-Barré syndrome provides an example of how the nerve centers are damaged by an inflammatory disease. In this case, the progressive weakness causes initial peripheral paralysis, or weakening of the arms and legs, which eventually ascends to the brain’s bulbar centers. This progressive palsy creates disorder within the brain’s motor neurons, causing loss of muscle control.
Bulbar palsy can also be caused by malignancy, such as a brain tumor. If the brain stem develops a tumor, or glomia, it may override normal brain and motor functioning. Motor function may be affected permanently, even if the tumor is detected and removed. The bacterial toxin that causes botulism creates muscular paralysis through the body’s bloodstream and affects lower motor functioning. Cases of botulism are rare in the developing world, making this the least likely cause of bulbar palsy.
Bulbar palsy is a degenerative disorder. The cranial nerves affected by bulbar palsy control the muscles responsible for chewing, swallowing, speech and, in some cases, breathing and facial movement. If any of these nerves are damaged, lower motor neurons are affected and palsy results. It is often confused with pseudobulbar palsy, which shares many of the same symptoms as bulbar palsy but is caused by damage to upper motor neurons resulting from stroke and affects different areas of the cerebral cortex.