[A circuitous route to the diagnosis of a very rare disease].

This case of a patient with Erdheim-Chester disease highlights the problems in diagnosing this very rare, largely unknown, but highly inflammatory non-Langerhans histiocytosis. This disease shows some characteristic clinical and molecular features including the BRAF V600E mutation, which was also demonstrated in this case in a perirenal tissue biopsy. The patient's condition improved under treatment with peginterferon alfa-2a and anakinra. However, remission for what is now 3 years was only achieved with the combination of anakinra and the BRAF inhibitor dabrafenib.