Low Bone Mass in Probable CD1a-negative Langerhans Cell Histiocytosis: A Diagnostic Challenge

Langerhans cell histiocytosis (LCH) is a rare disease characterized by CD1a/CD207-positive dendritic cells. This report presents a probable CD1a-negative LCH case in a 21-year-old man with chronic neck pain, low bone mass, and vertebra plana at the C6 level. Over 2 years, his symptoms progressed to severe vertebral collapse. Imaging and biopsy excluded malignancy and infection. Histopathology revealed a mixed immune infiltrate without CD1a expression, complicating diagnosis. LCH was confirmed through clinicoradiological correlation and exclusion of other disorders. Management included surgical stabilization and bisphosphonate therapy. This is the fourth reported CD1a-negative LCH case and the first associated with early-onset low bone mass for age. This case highlights diagnostic challenges and the importance of a multidisciplinary approach.