Abstract
Juvenile xanthogranuloma (JXG) is a clonal non-Langerhans cell
histiocytic disorder characterized by a variety of cutaneous and
non-cutaneous manifestations, predominantly in children. The
mitogen-activated protein kinase pathway (MAPK) is a key driver in many
histiocytic disorders, including JXG. We report a rare presentation of
JXG in the mastoid bone of a which recurred after surgery and was
refractory to two lines of chemotherapy before responding to the MEK
inhibitor trametinib, even in the absence of an identifiable MAPK
pathway mutation. MEK inhibitors may be a therapeutic option for this
sometimes difficult to treat disease.