Indeterminate cell histiocytosis in a patient with systemic lupus erythematosus and antiphospholipid antibody syndrome: an unusual association.

Indeterminate cell histiocytosis (ICH) is an extremely rare clonal proliferative disorder of dendritic cells which presents with skin lesions in the majority of cases. Although extra-cutaneous manifestations are very rare, ICH may involve the mucosa, cornea, and conjunctiva as well as the visceral organs. Since the clinical appearance of cutaneous lesions of ICH is not distinctive, it is diagnosed with histopathological and immunohistochemical findings after clinical suspicion. Herein, we report a 27-year-old man with a two-year history of asymptomatic reddish papules and papulonecrotic lesions on his face, arms and buttocks. He was previously diagnosed with systemic lupus erythematosus (SLE) and antiphospholipid antibody syndrome (APS), and he had been treated with hydroxychloroquine and low-dose aspirin. Diffuse dermal infiltration of a mixture of histiocytes and lymphocytes accompanied with multinuclear giant cells, the positive CD68 and Factor XIIIa and negative Langerin immunoreactions, along with the positive staining with CD1a and S100, led us to the diagnosis of ICH. To the best of our knowledge, this is the first case of ICH associated with SLE and APS.