The objective of this study was to determine the relationship between skin temperature and the level of IgM-rheumatoid factor (RF) in a patient with rheumatoid arthritis (RA).
This n=1 pilot study was self-performed (63-year-old man, RA-patient, IgM-RF-positive). Simple measures were applied for skin cooling, like light clothing and being outdoors. Skin temperature was measured every 5 min (24/7) on 1,635 days at the right wrist using a miniature temperature logger. Blood values of IgM-RF, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and anti-citrullinated protein antibodies (ACPA) were collected routinely.
In the first measuring period (A in figure 1A), the Spearman correlation coefficient between IgM-RF and the mean skin temperature of the 13 preceding weeks was unexpectedly high (r=0.80, n=16, P<0.001). Using longer or shorter periods than 13 weeks resulted in a decline of r. The experiment was repeated (B in figure 1A) and again a high correlation was found (r=0.83, n=42, P<0.001). In period B, the IgM-RF decreased to below the reference value (<16 IU/ml).
This pilot study argues that IgM-RF is associated with skin temperature in a single RA-patient.