Bendii Syndrome is a degenerative neurological illness affecting a minority of elderly Vulcans. Initially it is characterized by wasting, weakness, fatigue, fever, and a gradual but accelerating loss of emotional control, with victims exhibiting sudden bursts of emotion. Diagnosis is made by culturing tissue samples taken from the patient's metathalamus. There is no known treatment, but the disease is the focus of ongoing medical research.
A dangerous side effect of Bendii Syndrome is that the loss of emotional control can be telepathically projected to others. Vulcans are able to resist the emotional projections, but if the afflicted person is in the presence of non-Vulcans the emotions can cause outbreaks of violence. An attending Vulcan telepath can keep these projections under control, but when the sufferer is particularly stressed, the side effect can overwhelm such efforts.
- While the name of the affliction was generally pronounced "ben-dye", Perrin (Sarek's second wife) pronounced it "ban-dee" on at least one occasion.
- The illness is similar in nature to Alzheimer's disease.