Objective Rheumatoid arthritis (RA) is a chronic autoimmune disease of widely unknown etiology and pathophysiology. In this integrative single-case study on a patient with RA, we had the unique opportunity to closely monitor the individual dynamics of endocrine, immune and disease variables during a naturally occurring flare-up and subsequent medication change.

Methods The female RA patient collected her entire urine over 30 days in 12-h intervals (60 consecutive measurements in total). Subsequently, interleukin-6 (IL-6), orosomucoid-2, cortisol (ELISA), neopterin and creatinine (HPLC) levels were determined in the urine samples. Further, each morning and evening, the patient completed the DIARI, a set of questionnaires on variables such as subjective pain, subjective RA disease activity and emotional states. Once a week, besides an online video interview, the patient had an appointment at her rheumatologist, in which several indices of RA disease activity were determined: SDAI, CDAI and DAS28. From these data various time series were constructed for statistical analysis.

Results RA disease state increased from low to high activity during the first 12 study days. Thereupon, the medication was changed, which proved effective in reducing RA disease activity. However, the levels of urinary neopterin, urinary orosomucoid-2, and urinary IL-6 did not show any response, neither to the increasing disease activity nor the medication change. The patient’s daily reports on pain, RA disease activity, and emotional states, however, mirrored the course of the rheumatologic indices.

Conclusion This integrative single-case study clearly demonstrated the importance of process analysis for the evaluation of therapeutic measures in RA. In the patient studied, urinary levels of neopterin, orosomucoid-2 and urinary IL-6 were not found to be appropriate biomarkers of short-term fluctuations in RA disease activity. Instead, the results reported by the patient proved to be a useful tool for ambulatory and longitudinal monitoring of RA.

The authors have declared no competing interest.

This article was supported by the Innovation Committee of the Federal Joint Committee (G-BA) of the Federal Republic of Germany (funding number: 01NVF20024).

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Funding: This article was supported by the Innovation Committee of the Federal Joint Committee (G-BA) of the Federal Republic of Germany (funding number: 01NVF20024).

Conflicts of interest: None

All data produced in the present study are available upon reasonable request to the authors