Letter to the Editor: Lack of Attention to Epidemiological Study of Neuromyelitis Optica Spectrum Disorder Compared with that of Multiple Sclerosis in Iran

Neuromyelitis optica spectrum disorder (NMOSD) was once considered a type of multiple sclerosis (MS), but, due to differences in pathogenesis of these two diseases, NMOSD is currently considered as a totally separate entity and has different diagnostic criteria from MS.¹ Whereas MS is a demyelinating disease of the central nervous system, NMOSD is an astrocytopathic disorder. The incidence of NMOSD is much lower than that of MS, and, according to various reports, it varies from 0.51 per 100,000 people to 4.4 per 100,000 people.² Nevertheless, there are many clinical similarities between NMOSD and MS. Detection of NMOSD is crucial, because if it is not properly diagnosed it can threaten a patient's life. This distinction of NMOSD from MS is very important and emphasizes the 2017 McDonald criteria for MS diagnosis.¹ It has been suggested that in areas with a high NMOSD rate, each patient with MS should also be checked for NMOSD.³ Therefore, recognizing areas with a high prevalence of NMOSD is key.

Unfortunately, researchers have widely ignored epidemiological study of NMOSD in different regions of Iran. After performing a comprehensive survey on various sites including PubMed, Scopus, and Web of Science (ISI), only five epidemiological studies of the disease in Iran were found.^{2 4}–⁷ One was carried out in Khuzestan⁵ and two others in Isfahan.^{6 7} Two articles have evaluated NMOSD in Iran and in Iranian patients^{2 4}; however, they cannot show the overall epidemiology of the disease there and its distribution in different parts of the country. In the article by Sahraian and colleagues,⁴ only the clinical and demographic characteristics of 44 patients were studied; place of birth and place of residence of these patients were not discussed. The article by Eskandarieh and colleagues,² which is the most comprehensive study of NMOSD in Iran, is merely an examination of the epidemic aspects of the disease in Tehran, contrary to the title. Moreover, information about other regions of Iran was not found (Figure 1).

Iranian provinces where epidemiological studies of neuromyelitis optica spectrum disorder have been done (shown in red)

Therefore, taking the aforementioned studies into account, information on NMOSD is available only regarding three provinces, which cannot guide physicians given the prevalence of the disease in other regions of Iran. Meanwhile, according to a recent systematic study of the prevalence of MS in Iran,⁸ epidemiological studies of MS have been carried out in 31 provinces, which is truly significant. There is a need for more epidemiological studies of NMOSD in different regions of Iran, as such studies could help improve patient care.