MILAN – , according to a poster presented at the 9th Joint ECTRIMS-ACTRIMS meeting.
“There is a lack of education in differentiating between MS and NMO even in the medical community, which may result in a high misdiagnosis rate,” said study lead author Ka-Ho Wong, MBA, of the University of Utah, Salt Lake City, in an interview.
“NMO was recognized in the late 1800s and was historically thought to be a variant of MS until 1999,” said Michael Levy, MD, PhD, of Harvard Medical School and Massachusetts General Hospital, both in Boston, in an interview.
“They are both relapsing inflammatory disorders of the central nervous system with similarities in symptoms of weakness, numbness, mobility problem, vision defects, pain and fatigue,” said Dr. Levy, who did not take part in the new study. “A blood test for NMO was developed in 2004 and improved over time to the point that it can now reliably distinguish NMO from MS.”
As for therapy, “recent research has confirmed the two conditions are immunologically different and respond to different treatment,” Dr. Levy said. “The treatments developed for MS, especially from the 1990s, are harmful in NMO so it is important to make the diagnosis correctly.”
He added that “we do not recognize overlap between NMO or MS – it’s one or the other.”
Exploring the reasons for misdiagnosis
Mr. Wong, the present study’s lead author, said he and a research team launched the new study to better understand who gets misdiagnosed. “We know that almost 50% of the individuals get misdiagnosed at some point. However, what we don’t know yet is if the influencing factors are social determinants of health or if there are other causes.”
For the study, Mr. Wong and colleagues analyzed data from TriNetX, a health research network with access to medical records from 61 U.S. health care organizations. providing access to electronic medical records that includes sixty-one health care organizations (HCOs) in the United States.
ICD-10 coding statistics from 2008 to 2022 identified 7,657 patients with diagnoses for NMO. Of those, 4,040 (53%) only had diagnoses for NMO, and the rest (3,617, 47%) had diagnoses for both NMO and MS.
The researchers focused on 1,265 patients who had been coded for both diagnoses and had at least three clinical visits. They determined that a patient was misdiagnosed when they had three consecutive diagnoses of the same type. “For example, if they had MS but got misdiagnosed as NMO, once they are confirmed as MS they must have three or more consecutive diagnosis of MS to be considered as misdiagnosed,” Mr. Wong said.
Of the 1,265 subjects, the researchers determined that 308 (24%) had NMO but had been misdiagnosed as having MS, 189 (15%) had MS but were misdiagnosed as having NMO, and 768 (61%) were interchangeably diagnosed with the two conditions over time.
Among these three groups, 70.8%, 73.1%, and 78.4% were female, respectively; and 59.4%, 52.9%, and 53.0% were White, respectively. The percentages of Black patients were 17.2%, 24.3%, and 28.9%, respectively. Information about statistical significance was not provided in the poster.
Dr. Levy said he would “expect most NMO patients to initially be diagnosed with MS. It’s unusual to start with a diagnosis of NMO and then figure out it’s MS.”
As for the larger number of people with interchangeable diagnoses, Dr. Levy said that likely “reflects the messiness of billing codes.” For his part, Mr. Wong said there could be multiple causes for the interchangeable diagnoses: lack of disease knowledge, miscoding, lack of Food and Drug Administration–approved treatment for NMO at the time, and potentially other factors.