Snapshot A 1-year-old boy is brought to the emergency room for a new rash in the diaper area along with fever. On physical exam, along the inguinal folds, there are pink eroded papules on background of petechiae and purpura, as well as pink greasy discrete papules on the scalp and trunk. A radiograph of the cranium shows punched out lytic lesions. Introduction Overview login to view 2 more bullets Langerhan Cell Histiocytosis (LCH)Letterer-SiweHand-Schuller-ChristianHashimoto-Pritzker (Congenital Self-Healing Reticulohistiocytosis)Eosinophilic GranulomaDemographics< 2 years of age2-6 years of ageNeonatal period7-12 years of agePulmonary involvement seen in ages 30-40 yearsInvolvementSkin, bone, and viscerapulmonary infiltrates, lymph nodules, liver, and spleenSkin, bone, and visceraliver, spleen, and lymph nodesSkin-limitedPrimarily bone > skinPulmonary involvementPrognosisPoor prognosis with disseminated diseaseChronic and progressiveRapid spontaneous resolution is likelyGood prognosis Epidemiology Incidence login to view 1 more bullet Demographics login to view 1 more bullet Risk factor login to view 2 more bullets ETIOLOGY Pathogenesis login to view 4 more bullets Presentation Clinical Presentation of LCHLetterer-SiweHand-Schuller-ChristianHashimoto-Pritzker (Congenital Self-Healing Reticulohistiocytosis)Eosinophilic GranulomaSymptomsAcutely disseminated lesions affecting the skin, bone, and internal organsFeverBone painTriad of diabetes insipidus, osteolytic bone lesions (cranium), and exophthalmosSkin lesions that crust and resolves spontaneouslySolitary indolent bone lesions (cranium most common) with spontaneous bone fracturesPhysical examPink papules, pustules, vesicles, petechiae, purpura, and erosions on the scalp, flexural surfaces, and trunkSecondary impetiginization commonSkin findings similar to Letterer-SiweMultipe red to brown papulonodules, some with erosionsTenderness at site of bone lesions Other symptoms login to view 6 more bullets Imaging Bone radiograph login to view 4 more bullets Chest radiograph login to view 2 more bullets Studies Serum studies login to view 3 more bullets Urine studies login to view 1 more bullet Pulmonary function test login to view 1 more bullet Histology login to view 2 more bullets Electron microscopy login to view 1 more bullet Differential Multiple myeloma login to view 3 more bullets Treatment Medical login to view 17 more bullets Surgical login to view 3 more bullets Complications Bone fractures Hypercalcemia (from lytic bone lesions) Spontaneous pneumothorax Infections Hearing impairment Prognosis Worse with BRAF V600E mutation Worse if there is failure to respond to 6 weeks of treatment