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.