Langerhans cell histiocytosis with mesenteric involvement successfully treated with trametinib: a rare cause of small intestine obstruction.

Langerhans cell histiocytosis (LCH) is a rare type of histiocytosis with various clinical manifestations. The differential diagnosis for an infiltrative process in the mesentery includes histiocytosis, such as Erdheim-Chester disease (ECD) and Rosai-Dorfman disease (RDD), but mesenteric involvement has never been reported. Here we present the first documented case of LCH. A 24-year-old man presented with diabetes insipidus and was diagnosed with LCH via mesenteric biopsy, which demonstrated mesenteric involvement and the BRAFN486_P490del mutation. He was treated with trametinib 2 mg once daily, and FDG-PET/CT at 6 months after treatment initiation showed complete remission. Our report suggests that trametinib is a promising treatment option for non-BRAFV600E mutant LCH with mesenteric involvement.