Having 2nd autoimmune disease does not speed up MS progression: Study

Disability milestones reached at same rate as those without additional condition

Written by Steve Bryson, PhD | May 2026

• Having a second autoimmune disease does not speed up multiple sclerosis disability progression.
• Multiple sclerosis patients with another autoimmune condition reached disability milestones at the same rate.
• Older age at multiple sclerosis onset was the only factor linked to faster disability progression.

Having a second autoimmune disease does not accelerate disability progression in people with multiple sclerosis (MS), according to a large single-center study.

Among 1,230 MS patients followed over time, those living with an additional autoimmune condition that doesn’t affect the nervous system reached disability milestones at the same rate as those without one, even after accounting for age, sex, and time to treatment.

“Our findings suggest that concurrent [autoimmune diseases] do not independently accelerate long-term disability progression in MS,” researchers wrote in the study, “Comorbid autoimmune diseases do not influence long-term disability progression in multiple sclerosis,” published in Acta Neurologica Belgica.

MS frequently occurs alongside other autoimmune diseases

MS is an autoimmune disease in which the immune system mistakenly attacks the brain and spinal cord. It frequently occurs alongside other autoimmune diseases, including those that affect the liver (hepatitis), the digestive tract (inflammatory bowel disease), the skin (psoriasis), the eyes (uveitis), and the joints (arthritis).

Because MS and these conditions share an autoimmune basis, researchers believe they may also share underlying biological pathways and genetic risk factors. In fact, studies have found that people with MS and their relatives face a higher likelihood of developing another autoimmune condition, suggesting a genetic relationship.

But research examining whether a second autoimmune condition affects MS progression has yielded inconsistent results. To learn more, a group of researchers at Istanbul University in Turkey examined clinical data from 1,230 MS patients at a single treatment center: 95 had at least one other autoimmune condition not affecting the nervous system and 1,135 did not.

Among those with a second autoimmune condition, the most common were uveitis, an inflammatory eye disease (38.9%), and Hashimoto’s disease, a thyroid condition (34.7%). Other conditions included psoriasis (10.5%), rheumatoid arthritis (6.3%), ankylosing spondylitis (5.3%), and inflammatory bowel disease (4.2%).

The two groups were broadly similar at MS onset in terms of age, body weight, smoking status, family history of MS, and time to first treatment. But patients with a second autoimmune condition were more likely to be women (81.1% vs. 70.3%) and have a longer disease duration (median of 11.8 vs. 8.9 years).

Our study suggests that the presence of a comorbid [autoimmune disease] did not significantly alter the course of disability progression in MS. However, comorbid autoimmunity remains a critical factor in clinical practice because it can influence treatment-related complications and overall patient management.

When the team examined disability levels, significantly more MS patients with a second autoimmune condition had reached a moderate level of disability — a score of 3 or more on the 10-point Expanded Disability Status Scale (EDSS) — compared to those with MS alone (30.5% vs. 20.4%). However, the proportion of patients with an EDSS score of 6 or more, indicating more severe disability, was nearly identical between the two groups.

Importantly, when researchers analyzed the speed of worsening disability, there was no meaningful difference between the groups. That is, both reached moderate- and severe-disability milestones at the same pace.

The sole predictor of faster disability progression was the age at MS onset. Patients diagnosed after age 35 were 1.9 times more likely to reach a moderate disability milestone and 2.7 times more likely to reach the more severe milestone compared with those diagnosed at younger ages.

After statistical analysis that adjusted for all relevant factors, having a second autoimmune disease didn’t emerge as an independent driver of MS worsening. Final disability scores were nearly identical across both groups — an average of 2.1 for the MS-only group and 2 for those with an additional autoimmune condition.

“Our study suggests that the presence of a comorbid [autoimmune disease] did not significantly alter the course of disability progression in MS,” the researchers concluded. “However, comorbid autoimmunity remains a critical factor in clinical practice because it can influence treatment-related complications and overall patient management.”

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