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Swedes who developed osteoarthritis (OA) were at significantly increased risk for also developing multiple additional chronic diseases, researchers said.

With individuals in Sweden's Skåne region followed (via their medical records) for up to 20 years beginning in 1998, an OA diagnosis made in 2008-2009 was associated with subsequent development of severe multimorbidity at a relative risk of 2.45 (95% CI 2.12-2.83) compared with people without OA at that point, according to Andrea Dell'Isola, PhD, PT, of Lund University in Sweden, and colleagues.

People with severe multimorbidity in the study had an average of nearly 10 chronic illnesses, the authors noted in a . And development of even mild multimorbidity, with a mean of three chronic conditions, was heightened with a previous OA diagnosis (RR 1.29, 95% CI 1.12-1.48).

"Our findings strongly indicate that the individuals with OA are more prone to experience multimorbidity as they face an almost threefold higher risk of developing severe multimorbidity over 20 years, even after adjusting for common confounders like age, sex, and socioeconomic status," the researchers concluded.

OA is, of course, a common condition that comes with aging. But whether it promotes development of other debilitating diseases is an increasingly important question, as people around the world live longer thanks to improved healthcare, with OA becoming more common as a result.

"Systemic factors such as low-grade inflammation and metabolic dysregulation have been advocated as the missing link between OA and multiple conditions," Dell'Isola and colleagues observed. As well, OA could contribute to illnesses such as type 2 diabetes and cardiovascular disease by discouraging people from keeping physically active and diminishing social interaction.

Other studies have made connections between OA and multimorbidity, but, the researchers noted, these "fail to capture the variability of multimorbidity development over time."

For their own study, the group analyzed Swedish health registries for people age 40 or older who lived in Skåne, the country's southernmost region with a population of 1.4 million (roughly 12% of the national total), from 1998 to 2019. Individuals who received new diagnoses of OA in any joint, either as primary or secondary notations, in 2008-2009 were designated as cases; there were 9,846 such people. Each was matched by birth year, sex, and the year their records ended (either 2019 or the date of death or departure from Skåne) to two or more residents without OA diagnoses at any time; 19,692 such controls were included.

Mean age for cases and controls was 66 and 58% were women. Just over half the OA cases had knee arthritis, 25% had hip OA; the rest had OA of the hand or other joints, or "generalized" OA.

As of 1998, the vast majority of individuals had no more than one chronic condition. Subsequent multimorbidity trajectories were categorized into four groups: mild with late progression, mild with early progression, moderate, and severe. By the end of follow-up, average numbers of comorbidities for these four groups were 2.9, 3.1, 6.1, and 9.6, respectively.

Most importantly for the researchers' purpose, prevalence of OA in 2008-2009 among members of each category was as follows:

• Mild with late progression: 29%
• Mild with early progression: 31%
• Moderate: 35%
• Severe: 41%

The most common comorbidities were as expected: cardiovascular disease, malignancies, back pain, and cataracts stood head and shoulders above all others. More than 50 were tracked, spanning all major organ systems and including neuropsychiatric disorders. However, Dell'Isola and colleagues noted, "no discernible pattern of conditions in the identified trajectories" was found.

Limitations to the study included the reliance on administrative records and the potential that people with OA or other conditions didn't seek care for them. Also, "the role of physical activity, diet, and body weight in the relationship between OA and multimorbidity trajectories" could not be examined in these data, the authors acknowledged.

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