Anaplastic lymphoma kinase-positive histiocytosis with multisystem involvement: A case report.

Anaplastic lymphoma kinase (ALK)-positive histiocytosis is a rare disease that usually occurs in infants and young children and is characterized by ALK-positive histiocytes infiltrating organs. We present a case of multisystem involvement of ALK-positive histiocytosis in a female infant with skin nodules as the initial presentation. Despite multiorgan involvement, most tumors had spontaneously regressed, and all bones were partially healed after 40 months of regular follow-up without treatment. However, gait abnormalities persisted, indicating that early treatment may have greater impact in maintaining a child's quality of life when the disease involves the brain or the critical period of bone development.