Early comorbidities and diagnostic challenges in people with multiple sclerosis with possible impact on disease management.

Background: Comorbidities in people with multiple sclerosis (PwMS) can affect disease course and quality of life.

Objectives: To investigate comorbidities in the five years after diagnosis, timing of comorbidity occurrence, age and sex effects, and differences between multiple sclerosis (MS) and other chronic autoimmune diseases (AIDs).

Methods: In this retrospective cohort study, we systematically assessed differences in diagnosis frequencies in newly diagnosed PwMS (n = 9,880) compared to matched controls (noAID, n = 29,640) and individuals with other AIDs (psoriasis, n = 29,640; Crohn's disease, n = 9,880).

Results: Some comorbidities of PwMS are similarly frequent in other AIDs, while others, such as depression, are more prevalent in PwMS (odds ratio (OR) vs noAID = 2.03(1.94-2.13)). We found that personality disorders are more frequently recorded in PwMS before (OR  = 1.34(1.21-1.49)) and after MS diagnosis (OR  = 1.32(1.16-1.5)), especially in women (OR  = 1.39(1.2-1.6)). PwMS are more frequently diagnosed with Lyme disease (OR  = 1.98(1.69-2.33)), which was predominantly recorded by general practitioners after presentation with neurological symptoms. We observed lower acute tonsillitis frequencies in PwMS (OR  = 0.8(0.75-0.85)).

Conclusions: Our results suggest that PwMS might have a generally increased risk for specific personality disorders. More frequent Lyme disease recordings for PwMS suggest misdiagnoses of MS symptoms. Lower tonsillitis frequencies suggest a link between MS and protection from specific infections.