A Case of Juvenile Lupus with an Extremely Rare Dendritic Cell Malignancy: Interdigitating Dendritic Cell Sarcoma – Coexistence or Paraneoplastic Manifestation?

Systemic lupus erythematosus (SLE) is a prototypical autoimmune disease, characterized by circulating autoantibodies, widespread inflammation, and tissue destruction. The association between cancer and SLE is intriguing in view of their common pathophysiological pathways. It is established that there is an increased risk for overall malignancies in SLE, with standardized incidence ratios ranging from 1.14 to 3.6. Hematological malignancies are more common than solid organ malignancies in SLE. Malignancy when associated with lupus usually follows the diagnosis, but can occur concurrently or even predate the diagnosis of SLE. Neoplasms of dendritic cells (DCs), the key antigen‑presenting cells, are rare, and they account for <1% of all lymph node tumors. Interdigitating DC sarcoma (IDCS) is a rare hematological malignancy of DCs, with only a few over 100 cases being reported in literature. IDCS is usually seen in elderly males in their sixth decade. Here, we report a rare case of SLE and IDCS occurring together in a 5‑year‑old girl. The persistence of lymphadenopathy despite improvement in other lupus‑specific features following the initiation of treatment led to a suspicion of malignancy which was proven on histopathology. Another unique feature of our case was that remission and relapse of both SLE and IDCS occurred synchronously. Although this presentation is rare, clinicians must be aware of the possibility of SLE and malignancies occurring together, especially in the presence of atypical clinical manifestations such as persistent lymphadenopathy. This knowledge helps in early diagnosis and effective treatment of both these conditions. [ABSTRACT FROM AUTHOR]