Enigmatic Case of Adult-Onset Langerhans Cell Histiocytosis with Aggressive Bony Involvement.

Langerhans cell histiocytosis (LCH) is a rare hematologic neoplasm predominantly affecting children, with adult-onset cases being exceedingly uncommon. Neurological presentations, including spinal cord compression and cranial neuropathies, represent atypical manifestations that often lead to diagnostic delays. We present a 20-year-old previously healthy female who presented with progressive back pain, bilateral lower extremity weakness, and left-sided hearing loss. Imaging revealed a thoracic epidural mass causing severe spinal stenosis with additional diffuse osteolytic lesions. Initial biopsies showed nonspecific lymphoplasmacytic infiltrates. The patient subsequently developed cranial nerve palsies and dysphagia over several months. Definitive diagnosis required three biopsies, with the final petrous bone specimen demonstrating characteristic LCH histology and positive immunostaining for CD1a, S100, and Langerin. Treatment with zoledronic acid failed; subsequent therapy with cytarabine followed by cladribine plus hydroxyurea achieved partial radiographic and clinical improvement, though complicated by treatment-related sepsis. This case highlights the diagnostic and therapeutic challenges of adult LCH, given its rarity, variable presentation, and limited treatment guidelines. Multiple tissue samples with appropriate immunohistochemical staining may be required for diagnosis. Adult LCH treatment remains empirical, often extrapolated from pediatric data, with systemic therapies carrying significant toxicity risks. Greater awareness and adult-specific clinical trials are urgently needed.