Composite Measures in Rheumatology May Hamper Personalized Care

Composite indices are popular for the assessment of rheumatic and musculoskeletal diseases (RMD), but they may fail to accurately reflect the multidimensionality of individual patient outcomes in clinical practice, according to a review article published in the Annals of the Rheumatic Diseases.

“Composite indices have their value in clinical trials. A better signal-to-noise ratio adds to statistical power and limits the numbers of patients needed in the trial,” wrote corresponding author Robert B. M. Landewé, MD, PhD, of Amsterdam University Medical Center, and coauthor Désirée van der Heijde, MD, PhD.  “However, composite indices should give credit to the complexity of the disease, not by trying to lump all dimensions into one index, but rather to respect the time elapsed between cause and consequence and avoid mixing both up.”

Rather than a single multidimensional index, using multiple unidimensional indices—or describing separate components of a composite index as secondary outcomes partnered with a unidimensional index—may better reflect the versatility of an RMD, they explained.

“When application of composites in clinical practice is in question, multidimensional composites lose their value,” they added, “since interpretational mistakes are too easily made, and patients may fall victim to benchmark medicine.”

Unidimensional composites, too, can mix different perspectives. For example, a patient with rheumatoid arthritis with a high Disease Activity Score but low inflammation may not be best served through composite indices but rather by swollen joint counts, acute-phase reactants, or a physician with expertise in detecting inflammation clinically, the writers pointed out.

“Parsimony in outcome assessment can unintentionally lead to loss of subtlety and harm rather than benefit patients in clinical practice,” they wrote.

—Jolynn Tumolo

Reference:

Landewé RBM, van der Heijde D. Use of multidimensional composite scores in rheumatology: parsimony versus subtlety. Annals of the Rheumatic Diseases. 2021;80:280-285. doi.org/10.1136/annrheumdis-2020-216999