| Summary: | Erdheim-Chester disease (ECD) is a rare form of non–Langerhans cell histiocytosis characterized by infiltration of organs by CD68+ and CD1a− lipid-laden histiocytes, including the central nervous system in more than a third of patients. Molecular analysis of ECD samples has demonstrated the prevalence of BRAF V600E mutations as high as 54%. Recently, vemurafenib became the only Food and Drug Administration–approved treatment for patients with ECD who carry the BRAF V600E mutation. However, dabrafenib has been suggested to have greater brain distribution. We describe a 44-year-old female patient treated from August of 2015 through November 2017. She presented with a 2-year history of light-headedness, fatigue, and vertigo. She was moderately dysmetric, diffusely hyperreflexic, and dysarthric in the bilateral upper and lower extremities. Her gait was wide-based. She had dysarthria and nystagmus on horizontal gaze bilaterally. Magnetic resonance imaging showed an extensive area of increased T2/fluid-attenuated inversion recovery signal in the brain stem, enhancement in the pons and midbrain, and thickening of the pituitary stalk. Positron emission tomography/computed tomography (PET/CT) and whole-body technetium Tc99m bone scintigraphy showed intense symmetrical radiotracer uptake in the distal femur and tibia bilaterally, which was biopsied. Immunohistochemistry was negative for BRAF V600E, but genomic sequencing revealed the mutation. The patient received combination therapy with dabrafenib and trametinib. Her nystagmus, dysarthria, dysmetria, and gait improved remarkably. Subsequent PET/CT and magnetic resonance imaging showed complete resolution of all radiographic evidence of disease. In this case report, we demonstrate the success of a combination therapy with dabrafenib and trametinib.
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