ALK-positive anaplastic large cell lymphoma initially diagnosed as neurosarcoidosis in a 12-year-old girl.

We present a rare case of optic neuropathy due to anaplastic lymphoma kinase-positive (ALK+) anaplastic large cell lymphoma (ALCL) with optic nerve infiltration in a 12-year-old girl who presented with acute unilateral vision loss, diplopia, and headache after two prior hospitalizations at an outside facility for disk edema. She had a presumptive diagnosis of neurosarcoidosis and empiric treatment had been initiated with high-dose corticosteroids. Ongoing worsening of vision prompted presentation at our facility. Histopathological examination from a cervical lymph node biopsy revealed ALK+ ALCL with central nervous system involvement. The patient's vision returned after initiation of chemotherapy. This case highlights the importance of considering malignancy in the differential for optic neuritis.