Neuromyelitis optica (NMO) is a central nervous system inflammatory autoimmune disease characterized by medullary and/or optical nerve damage. It is rare but life-threatening. Concerning the treatment of NMO, many drugs have been used in background therapy. Some studies have shown efficacy of rituximab (an antiCD20 monoclonal anti-body) either on the reduction of the annual number of exacerbation or the mean score EDSS. In 2013, a Korean team reported a new protocol during which they administered rituximab only when memory B lymphocytes CD27+ were detectable in the bloodstream. In our patient, institution of this protocol led to clinical benefit with a major decrease in the EDSS score over time (7 in August 2012 vs. 1 in October 2015), a reduction of the total administered dose (4g in 2013 vs. 1.375g in 2014 vs. 0g in 2015) and side effects. Compared with the rate of theoretical administration, health expenditure savings reached 1700 Euros per month over the 11-month treatment. Monitoring therapeutic response markers with memory B lymphocyte counts appear to be an efficient cost-effective way to measure clinical efficiency, reduce total doses, and limit side effects.