Usually NMO occurs as a series of episodes or relapses. However, in approximately 10% of patients, it appears that a form of monophasic NMO exists. These patients may suffer from an acute episode of optic neuritis in one or both eyes, and have other hallmark signs such as transverse myelitis, but have no relapses. However, it is difficult to tell if such patients are in a long remission period, or have the monophasic form of disease, so drug treatment is usually continued.