Bendii Syndrome

  A rare usually fatal disease that afflicts Vulcans over the age of 200, debilitating their emotional control; there is no known treatment.

Early symptoms include sudden bursts of emotion, especially irrational anger, but the only way to prove a diagnosis is to grow a culture from tissue of the metathalamus — a process which takes several days. The telepathic abilities of Vulcans are strong enough to cause the loss of control to be projected onto others.
Ambassador Sarek of Vulcan died of it on stardate 45245, in 2368.