The majority of patients in the present study had JIA and were using non-biological immunosuppressive medication. The most common symptoms were fever and weight loss, and a predominance of cases of PTB was noted.

The MoH-Brazil scoring system resulted in a possible or highly probable diagnosis of TB in 88% of PTB cases, highlighting the method’s significance in diagnosing PTB in children.

The TB-MRT was positive in 45% of the samples, which is a similar percentage to the EPTB cases in the previous study conducted in our institution [12]. However, our patients whose samples were sent for bacilloscopy and culture were negative, which reinforces the fact that children are paucibacillary [3].

Laboratorial alterations found could be explained by the RD itself, as well as the treatment involved. MTX and hydroxychloroquine are known for their hematological adverse effects as: anemia, leukopenia and low platelets [13, 14].

From the 1992 patients with RD followed-up at the pediatric rheumatology unit, 8 developed TB between 1995 and 2020 and 7 developed TB between 2021 and 2022, corresponding to 0,83% of the exposed patients. Our finding is similar to a study conducted in Portugal with adults under TNF-therapy from 2006 to 2019 [15].

In our cohort, we had a presumed prevalence of 33,3% (15/45) of TB disease. The higher prevalence of TB could be explained by the degree of immunosuppression in patients with RD and the medications they were taking [5, 6, 16] In addition, the study was conducted in a reference center for childhood TB, with a high number of the disease in this age group. As well, in childhood TB, approximately 20% of cases are EPTB [3]. However, in this study, 40% of patients with RD were diagnosed with EPTB.

In our case series, MTX was the most used medication for the treatment of RD, which could be explained by the period of the research (from 1995 to 2022), once the first biological agents, of the anti-TNF class, began to be prescribed in 2004, with still limited access, in this pediatric rheumatology unit. Furthermore, MTX is the first-line treatment prescribed for most cases of JIA [17]. Also, all patients were screened for latent TB and TB previous to any specific treatment for a given RD.

Despite screening prior to treatment, the use of anti-TNFα medications is associated with an increased risk of TB activation. Additionally, false negative TST due to immunosuppression caused by the RD or previous immunosuppressive therapy is a possibility [18].

In our case series, the fatal case of polyarteritis nodosa and miliary TB had factors that are known triggers of MAS. In an integrative review on TB in children with RD, the only reported death occurred in a patient who sequentially used etanercept, adalimumab, and abatacept and had EPTB [19]. Both patients underwent anti-TNFα therapy, which may be related to the severity of TB.

The limitations of our study include the small sample size and retrospective design, which presents challenges in obtaining some data due to incomplete information registration.