Adolescent-and-Young-Adult-Onset Multisystem Langerhans Cell Histiocytosis With Central Nervous System Involvement: A Case Report.

Langerhans cell histiocytosis (LCH) is a proliferative disorder causing normally immune-responsive Langerhans cells to abnormally accumulate in various tissues and organs. Most available data on LCH is derived from pediatric populations, with limited literature focusing on adult LCH, which is rarer. Multisystem involvement in LCH, including central nervous system (CNS) involvement, is often higher risk and poorer prognosis. Standardized treatment recommendations remain limited, particularly in adolescent and young adult (AYA) populations. Discussed below is a case of AYA-onset multisystem LCH with CNS and skeletal system involvement, which was successfully treated with cladribine therapy. An 18-year-old male with no significant past medical history presented with left orbital pain and swelling. Laboratory, imaging, and biopsy results were consistent with a diagnosis of multisystem LCH. The patient was started on cladribine at 0.1 mg/kg/day for 7 days, along with Pneumocystis pneumonia prophylaxis and symptomatic management of facial pain and headaches. After four cycles of cladribine therapy, the patient exhibited symptomatic resolution and complete response of CNS and skeletal lesions. This highlights one potential therapeutic approach yielding a favorable outcome in a borderline case of AYA-onset LCH without targetable mutations on tissue next-generation sequencing (NGS). It also underscores the need for systemic therapy in patients with CNS involvement to avoid future long-term neurodegenerative complications. Further prospective studies and clinical trials are warranted to yield standardized treatment regimens for adult patients with LCH, particularly with multisystem involvement, including CNS.