Progressive Cranial Polyneuropathy and Myelopathy as the Initial Manifestation of Leucine Zipper 4-Positive Paraneoplastic Syndrome in Previously Undiagnosed Metastatic Testicular Seminoma

A 50-year-old man without a significant medical history developed progressive double vision from a partial right third nerve palsy, as well as right-sided hyperreflexia and decreased temperature sensation in his right hand. Initial contrast MRI of the brain revealed enhancement of the right oculomotor nerve. Cerebrospinal fluid and serologic studies were negative or normal. Over the next 6 weeks, he developed a left sixth nerve palsy and right-sided facial sensory changes, followed by a partial left third nerve palsy and right foot drop. The patient later disclosed a 2-year history of painful right hemiscrotum swelling. Abdominal imaging and testicular biopsy revealed a Stage IIA testicular seminoma and was treated with radical orchiectomy, steroids, intravenous immunoglobulin, and chemotherapy. He continued to deteriorate, with evidence of myelitis on thoracic MRI. Initial paraneoplastic studies were negative, and research-based antibody testing revealed leucine zipper 4 autoantibody positivity, indicating a paraneoplastic syndrome.