NMOSD, MS Tied to Higher Risk for Parkinson’s in South Korea
NMOSD patients in study were 2.61 times more likely than controls to develop PD
Patients with neuromyelitis optica spectrum disorder (NMOSD) or multiple sclerosis (MS), another disease that damages the protective myelin sheaths around nerve cells, are at higher risk than healthy individuals of also developing Parkinson’s disease (PD), a South Korean study found.
The study, “Risk of Parkinson’s disease in multiple sclerosis and neuromyelitis optica spectrum disorder: A nationwide cohort study in South Korea,” was published in the Journal of Neurology, Neurosurgery & Psychiatry.
Both NMOSD and MS are demyelinating diseases that occur when the immune system mistakenly attacks the myelin that ensheathes the nerve cells to increase the speed at which they send off messages to other cells in the body.
As the nerve cells begin to waste away over time as a result of the attack, they can no longer carry away the messages sent by the brain to order muscles to take action. This causes patients to lose control of their movements, but other symptoms may also appear.
In NMOSD, the attack is mainly directed toward the spinal cord and the nerves of the eyes, called optic nerves. This means that patients will most often experience a range of symptoms, from eye pain and loss of vision to muscle weakness and spasms, loss of coordination, and changes in sensation.
Parkinson’s occurs when some nerve cells in the brain are lost, causing tremor, slow movements, and stiff muscles, among other motor and nonmotor symptoms. While there is a parallel between some of the symptoms of demyelinating diseases and those of Parkinson’s, it has been unclear whether NMOSD and MS may increase the risk of developing Parkinson’s.
Some previous studies found that patients with MS are more likely to develop Parkinson’s, but others failed to find a link between the two diseases. There are no known studies in NMOSD and Parkinson’s.
In this study, a team of researchers in South Korea drew on data from the Korean National Health Insurance Service (KNHIS) database, in what they say is “the first population-based cohort study” to compare how likely patients with NMOSD are to develop Parkinson’s versus a matched control population.
The KNHIS registry covers up to 97% of the population in South Korea. Data from 1,490 NMOSD patients and 1,380 people with MS were collected between the beginning of 2010 and the end of 2017.
All were 40 years or older, and none had received a diagnosis of Parkinson’s before or within one year following their diagnosis of NMOSD or MS. Each patient was compared to five healthy (control) individuals who had the same age and sex. They also were matched according to the presence of three risk factors for PD: diabetes, hypertension (high blood pressure), and dyslipidemia (abnormal levels of blood fats).
Of the patients with NMOSD, 497 (33.4%) were men. Their mean age was 54.9 years, and most (82.8%) were in the age range of 40 to 64 years. The most common disease coexisting with NMOSD was dyslipidemia (31.7%), followed by hypertension (30.0%), and diabetes (21.5%). Patients were followed up for a mean 4.2 years, and their matched controls were followed up for about the same time.
Patients at risk
During this period, there were eight new cases of Parkinson’s among NMOSD patients. When calculated per 1,000 person-years, this figure translated into an incidence rate of 1.27, which was higher than that of controls (0.55). This means that patients with NMOSD were 2.61 times more likely than controls to develop Parkinson’s.
Patients with MS were at even higher risk. Of all patients with MS included, 580 (42%) were men. Their mean age was 56.8 years, with roughly three-quarters (77.1%) falling in the age range of 40 to 64 years. There were 625 (45.3%) patients with hypertension, 442 (32.0%) with dyslipidemia, and 240 (17.4%) with diabetes.
During a mean follow-up of 4.5 years, the incidence rate of Parkinson’s was 3.38 per 1,000 person-years, which was higher than that of controls (0.42). This translated into patients with MS being at a 7.73 times higher risk of Parkinson’s than controls.
Age, sex, and the presence of diabetes, hypertension, and dyslipidemia did not play a statistically significant part in further increasing the risk for Parkinson’s. While this may contradict previous findings that suggested these diseases as risk factors for Parkinson’s, the researchers noted that “the dose and type of medications to control” them were not taken into account.
The study did not delve into the mechanisms driving the development of Parkinson’s in patients with NMOSD or MS, but the researchers put forward some possibilities. One of them has to do with alpha-synuclein, a protein that builds up into toxic clumps in nerve cells of patients with Parkinson’s and is also found in the cerebrospinal fluid (the liquid around the spinal cord and brain) of those with NMOSD or MS.
Other possibilities involved mitochondria (the powerhouses of cells) and astrocytes, star-shaped cells that give support to nerve cells. Both may go awry in NMOSD and MS, and this could contribute to the loss of nerve cells in Parkinson’s.
Moreover, patients with NMOSD or MS “tend to have a higher awareness of subtle neurologic deficits,” the researchers wrote. These patients also undergo “regular neurologic examinations from neurologists,” which could increase the number of diagnoses of Parkinson’s.
“Further epidemiological and clinical studies are needed to replicate our findings,” the researchers concluded.