Multiple sclerosis is far more prevalent among African Americans than previously suspected. In fact, a new study published in the journal Neurology found that black patients were nearly 50% more likely to develop the disease than whites.
Researchers examined the health records of more than 3.5 million Kaiser Permanente health system patients over a three year period. In an average year, 10 out of every 100,000 blacks developed multiple sclerosis (MS); compared to 7 white patients, 3 Hispanics and 1 Asian for every 100,000 people.
“Our findings do not support the widely held belief that blacks have a lower risk of MS than whites, but that MS risk is determined by complex interactions between race, ethnicity, sex, environmental factors and genotypes,” said lead author Annette Langer-Gould, MD, of the Kaiser Permanente Southern California Department of Research & Evaluation.
The study found that 70% of MS cases occur in females, but it was more pronounced among black women than white women.
Additionally, black women had a higher incidence of MS than white patients of both sexes, while black men had a similar risk of being diagnosed with MS compared to white men. The lower risk among Hispanic and Asian patients was true for both sexes.
“Although additional research is needed, possible explanations for the higher incidence of MS in black women include a greater prevalence of hormonal, genetic, or environmental risk factors such as smoking, compared to patients from other racial or ethnic groups,” said Dr. Langer-Gould.
Researchers say that the belief MS is rare in blacks is based on previous studies, including one study of Korean War veterans in the 1950s, which found white men were twice as likely to receive disability compensation for MS as black men.
“A possible explanation for our findings is that people with darker skin tones have lower vitamin D levels and therefore an increased risk of MS,” said Langer-Gould. “However, this does not explain why Hispanics and Asians have a lower risk of MS than whites, or why only black women but not black men are at a higher risk of MS.”
She also pointed out that most MS clinics are in predominantly white areas, skewing how people perceive the disease.
Whether the new study indicates a rise in MS cases among blacks or an underestimation in previous studies is unclear, but a neurologist not involved in the study says the results strongly imply “that the rate has really gone up in blacks.”
If there has been an increase in blacks’ risk, said Dr. George Ebers, a neurologist who studies MS at John Radcliffe Hospital at the University of Oxford, it would have to be due to the environment, since genes wouldn’t change that much over a couple of generations.
“This may be the conjunction of the Western lifestyle,” Ebers told Reuters Health. “Plus the fact that they’re living in the relatively northern section of the world,” where there’s less vitamin D from sunlight.
Because of the notion that they’re at lower risk, Dr. Langer-Gould believes that many black patients are initially misdiagnosed,
“This is a disease that affects all racial and ethnic groups,” she told Reuters Health.
“If somebody comes in with symptoms that are suspicious for it, particularly blacks, those symptoms should be taken seriously and worked up and not assumed that it can’t possibly be MS because they’re the wrong race or ethnicity.”
An estimated 19,000 people per year are newly diagnosed with MS in the U.S. The average age for MS diagnosis is 41 years.
The study also found that the median time from symptom onset to MS diagnosis was four months, but could be as long as 40 years. Hispanic and Asian patients were generally younger at the time of MS diagnosis than white and black patients.
MS is a chronic, often disabling disease that attacks the central nervous system, destroying the protective myelin sheath that protects nerve cells in the brain, optic nerve and spinal cord.
Symptoms may be mild, such as numbness in the limbs, or severe, such as paralysis or loss of vision. The progress, severity and specific symptoms of MS are unpredictable and vary from one person to another.
An estimated 400,000 Americans have the disease and more than 2 million worldwide. There is no known cure.