A common presentation - turning out as an uncommon diagnosis: From hip pain to Langerhans cell histiocytosis.

Langerhans cell histiocytosis (LCH) is an uncommon clonal proliferation of myeloid progenitor cells, it is especially rare in adults. We present a case of multi-system LCH in a 53-year-old woman, the sole symptom of which was prolonged, non-resolving hip pain for 18 months prior to the diagnosis. Initial evaluation included imaging studies aimed at identifying a presumed local etiology. X-ray demonstrated non-specific arthritic changes on the left femur. Computed tomography (CT) and magnetic resonance imaging (MRI) scans identified a lytic lesion at the same location, warranting a systemic workup. After non-invasive investigations failed to reveal the underlying etiology, a biopsy was performed, revealing cores of Langerhans cells that stained positive for both CD1a and langerin. These findings verified the surprising, uncommon diagnosis of LCH. A comprehensive workup was conducted in order to determine the extent of the disease and its molecular nature - revealing a BRAFV600E-positive, high-risk, multi-system LCH with skeletal, lung and liver involvement.