Lymphopenia as an Independent Marker of Disease Activity in Children with Systemic Lupus Erythematosus

Background: Lymphopenia is associated with disease activity in adult patients with systemic lupus erythematosus (SLE), but no similar studies exist among children. Furthermore, lymphopenia has only been used as a parameter of disease activity in the SLE disease activity index (SLEDAI), but not as an independent marker. Objectives: This study aimed to ascertain lymphopenia as an independent marker related to disease activity in children with SLE. Methods: This was a retrospective cohort study on patients newly diagnosed with SLE. The data were collected from January 2009 to March 2017, including clinical manifestations, complete blood counts, anti-dsDNA, and Mexican-SLEDAI (MEX-SLEDAI) scores. Statistical analysis was performed using the Chi-square test, Student's t-test, and ROC curve analysis. Results: A total of 103 patients, aged from 12 to 18 years, participated in the study. Of these, 58 patients (56.3%) exhibited lymphopenia. The most commonly observed clinical manifestations in the lymphopenia group included nephritis (72.4%), hypertension (24.1%), and leukopenia (36.2%), with p < 0.05. Furthermore, neuropsychiatric SLE was found exclusively in the lymphopenia group. A negative correlation was observed between lymphocyte counts and anti-dsDNA levels (r = -0.24), as well as between lymphocyte counts and the MEX-SLEDAI score (r = -0.63, with p < 0.05). The receiver operating characteristic (ROC) curve indicated that a lymphocyte count with a cut-off point of ≤1738/mm³ is significant for predicting anti-dsDNA reactivity. Conclusions: Lymphopenia is significantly correlated with higher anti-dsDNA levels and increased disease activity, potentially serving as an independent marker of disease activity in children with SLE. However, further research is needed.