Serum soluble interleukin‐2 receptor level is more sensitive than angiotensin‐converting enzyme or lysozyme for diagnosis of sarcoidosis and may be a marker of multiple organ involvement

Skin lesions in sarcoidosis are often the initial symptoms that enable the dermatologist to be the first to diagnose this granulomatosis. However, diagnosis is sometimes very problematic. In 2015, the diagnostic criteria for sarcoidosis were updated in Japan, with elevated serum soluble interleukin‐2 receptor (sIL‐2R) replacing negative tuberculin reaction. Therefore, we assessed the clinical utility of sIL‐2R compared with two other common markers, angiotensin‐converting enzyme (ACE) and lysozyme, in patients who visited the dermatology clinic. Data from 72 patients showed that sIL‐2R was more sensitive than both ACE and lysozyme in supporting a diagnosis of sarcoidosis (52.8%) compared with ACE (29%) and lysozyme (26.4%). Additionally, the sIL‐2R level was significantly higher in patients with multiple organ involvement and parenchymal infiltration. Patients with elevated sIL‐2R levels had higher serum ACE and lysozyme levels, a higher incidence of pulmonary involvement, more severe chest radiographic stage and a high incidence of expression‐specific signs by imaging analysis. Receiver–operator curve analysis showed that sIL‐2R was a better marker at the threshold cut‐off point compared with ACE and lysozyme for identifying patients with multiple organ involvement, detecting patients with pulmonary disease and parenchymal infiltration as well as predicting the presence of specific signs in the diagnosis of sarcoidosis. Moreover, the kinetics of sIL‐2R levels correlated closely with clinical manifestations, in contrast to the modest changes of ACE and lysozyme levels during the follow‐up period. In conclusion, sIL‐2R may be considered a good marker for diagnosis and a potential indicator of disease activity.