Professor ZHOU Zhongying put forward Fu Du"（hidden toxin

伏毒） theory in the syndrome differentiation of diagnosis and treatment of acute and severe diseases. Fu Du is believed to be endogenous or exogenous pathogenic factors concealing in a certain part of the body

which has the pathogenic characteristic of "hiding in human body not being detected until being exposed by the occurrence of disease". Neuromyelitis optica spectrum disorder（NMOSD） is a kind of acute and severe autoimmune disease. It often attacks repeatedly and is difficult to be cured. Patients with NMOSD have the deficiency of essence and pathogenic factors hiding in the body. When something external cause actuates the hidden pathogenic factors

the disease will attack

which is in accordance with pathogenesis of Fu du

and the toxin of NMOSD is specific. Therefore

the pathogenesis

clinical characteristics and treatment scheme of NMOSD is discussed according to "Fu Du" theory.