[Erdheim-Chester disease: a rare histiocytosis with outstanding response to cobimetinib.]

Erdheim-Chester Disease (ECD) is a rare form of histiocytosis, characterized by xanthogranulomatous infiltration of multiple organs by lipid-laden histiocytes. It is considered a myeloid inflammatory clonal disorder that mainly affects men with a mean age of 55 years.

We present the case of a 65-year-old man who consulted our Endocrinology Unit because of polyuria and polydipsia of 4 months of evolution, diagnosing central diabetes insipidus associated with pituitary infiltration. Physical examination showed skin lesions he has had for several years, that were papules-nodules in the anterior chest and xantelasma-like in the face and neck, with biopsy compatible with non-Langerhans histiocytosis. The genetic study of the skin biopsy showed the presence of a mutation in MAP2K1, confirming the ECD.

The patient started treatment with interferon alfa, but the response was incomplete and associated with severe intolerance, so given the findings of the genetic study, we decided to indicate treatment with cobimetinib, a potent and selective inhibitor of MEK. After 8 months of treatment, skin lesions have disappeared, as has the pituitary infiltration, with a remarkable improvement in his quality of life.

We present a 65-year-old patient with a rare form of histiocytosis (ECD) who in turn presented an atypical form of ECD and, where the genetic study allowed us to confirm the diagnosis and use targeted therapy with cobimetinib with outstanding results.