Study Compares Patients With RA and Those Without to Determine Multimorbidity Prevalence, Incidence

Multimorbidity affects 1 in 4 US adults and leads to increased health care use and lower quality of life.

Using a well-known set of population data, researchers sought to estimate the prevalence and incidence of multimorbidity—a separate concept from comorbidity—in patients with rheumatoid arthritis (RA) compared with those without RA.

Multimorbidity, the researchers wrote in their report, published in The Journal of Rheumatology, is focused on the patient rather than the disease and is limited to chronic conditions.

“This concept is useful in patients with RA because it is reflective of patient complexity and the associated challenges in providing care for patients with RA who have multiple chronic conditions (eg, the influence of other chronic conditions on RA treatment response),” the researchers said.

While multimorbidity is typically outlined as the co-existence of 2 or more chronic conditions, definitions of 3 or more chronic conditions and definitions based on 5 or more classes of medications have also been used, and there is no consensus on a list of conditions.

In the United States, multimorbidity affects 1 in 4 adults and leads to increased health care use and lower quality of life.

In the general population, the most commonly used indices are the Charlson comorbidity index (CCI) and the Elixhauser comorbidity index (ECI); 2 indices, the rheumatic disease comorbidity index (RDCI) and multimorbidity index (MMI) are specific in patients with rheumatic diseases,

The researchers said they undertook the study because the extent of the burden of multimorbidity in patients with RA compared with those of similar age and sex is not well known.

The study used the data of the Rochester Epidemiology Project (REP), which, for more than 50 years, has provided to researchers the inpatient and outpatient medical records of residents of Olmsted County, Minnesota. A nurse abstractor manually reviewed the records for the patients who fulfilled the 1987 American College of Rheumatology (ACR) classification criteria for RA between 1999 to 2013.

In addition, data on positivity for rheumatoid factor (RF) and anti-cyclic citrullinated peptide antibody (ACPA) were included; patients positive for either RF or ACPA were considered to be seropositive.

Patients were compared with age and sex-matched non-RA subjects from the same population.

Rheumatic comorbidities were excluded, and 25 chronic comorbidities from a combination of the Charlson, Elixhauser and Rheumatic Disease Comorbidity Indexes were included. The comorbidities included cancer, metastatic cancer, chronic pulmonary disease, heart failure, dementia, diabetes, myocardial infarction, cerebrovascular disease, valvular disease, liver disease, paralysis, peripheral vascular disorders, renal failure, alcohol and substance abuse, coagulopathy, deficiency anemias, depression, hypertension, hypothyroidism, psychoses, other neurological disorders, pulmonary circulation disorders, HIV, AIDS, and spine, hip or leg fractures.

Aalen-Johansen methods were used to estimate the cumulative incidence of multimorbidity (2 or more chronic comorbidities) or substantial multimorbidity (5 or more), adjusting for the competing risk of death.

The study included 597 patients with RA and 594 non-RA subjects (70% female, 90% Caucasian, mean age 55.5 years). Forty percent of the patients with RA were obese.

At incidence/index date, the prevalence of multimorbidity was higher in RA than non-RA subjects (38% RA vs. 32% non-RA, P = .021) while prevalence of substantial multimorbidity was similar (5% RA vs. 4% non-RA, P = .68).

Both groups had hypertension as the most common comorbidity; when hypertension was excluded in groups with 2 or more or 5 or more chronic conditions (MM2+ and MM5+), the increased risk of having higher multimorbidities in RA vs non-RA persisted.

During follow-up, which was a little more than 11 years for both groups, more RA patients developed multimorbidity (214 RA vs. 188 non-RA; adjusted hazard ratio (aHR), 1.39; 95% CI, 1.14-1.69).

By 10 years after RA incidence/index, the cumulative incidence of multimorbidity was 56.5% among patients with RA (95% CI, 56.5%-62.3%) compared with 47.9% among those without RA (95% CI, 42.8%-53.7%).

Patients with RA showed no evidence of increase in incidence of substantial multimorbidity (aHR, 1.17; 95% CI, 0.93-1.47).

In discussing the findings, the researchers noted that systemic inflammation characterizes RA, and that could explain the higher prevalence of multimorbidity both at RA incidence the development of comorbidities after RA incidence. Patients with RA had a higher prevalence of multimorbidity at RA incidence and a higher incidence of 2 or more during follow-up compared with those without the disease.

Looking at patients who were negative or positive to RF and ACPA, seronegative patients with RA had more morbidities at RA incidence than those who were seropositive; both subgroups had similar incidence of 2 or more or 5 or more multimorbidities after RA incidence.

The researchers said the findings underscore the “increasing need for rheumatology care models that provide support for addressing multimorbidity and for improved coordination of healthcare between rheumatologists and primary care providers.”


Gunderson TM, Myasoedova E, Davis JM, Crowson CS. Multimorbidity burden in rheumatoid arthritis: A population-based cohort study. J Rheumatol. Published online February 15, 2021. doi: 10.3899/jrheum.200971