Multiple Drug Regimen-Refractory Rosai–Dorfman–Destombes Disease Mimicking Relapsing Polychondritis Successfully Treated with Cobimetinib

Rosai–Dorfman–Destombes disease (RDD) or sinus histiocytosis with massive lymphadenopathy is a rare non-Langerhans cell histiocytosis of unknown cause. The disease often manifests as painless bilateral cervical lymphadenopathy associated with systemic symptoms such as fever and weight loss. Extranodal disease is also frequent and can involve any organ, mostly the skin, nasal cavity, bone, and retro-orbital tissue. Swelling of cartilaginous tissues, such as the helix of the ear or laryngeal structures, may mimic the entity known as relapsing polychondritis. Although spontaneous remission is the most expected evolution, some cases require systemic treatment with prednisone, methotrexate or cytotoxic agents, with variable rates of success. In this respect, since somatic variants in the genes involved in the mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinases (ERK) pathway have been observed to play a pathogenic role in RDD. Therefore, the use of therapies targeting these pathogenic variants appears to be a reasonable strategy. Here we present the case of a 37-year-old woman with RDD and extensive extranodal involvement that showed a rapid and complete response to the MEK inhibitor cobimetinib