Dyad of Infantile Cutaneous and Thymic Langerhans Cell Histiocytosis: Is It Rare?

This report discusses a rare case of an 8-month-old infant with both cutaneous and thymic Langerhans cell histiocytosis (LCH), highlighting the potential underdiagnosis of thymic involvement in LCH. Thymic involvement is rare, affecting only 2.6% of LCH patients, and is typically identified through imaging techniques like ultrasound or MRI. The case emphasizes the importance of considering thymic sonography in the staging evaluation of infants with cutaneous LCH, as it can reveal subtle findings that might be missed on CT scans. The infant in the study responded positively to chemotherapy, but experienced disease recurrence, which was managed with trametinib targeting a BRAF V600E mutation. The authors suggest that thymic LCH may be underdiagnosed and propose further research and consideration of thymic ultrasound in LCH staging, especially in infants, due to its potential impact on treatment decisions.