Paraneoplastic neurologic syndromes (PNS) are rare disorders associated with the remote outcomes of cancer, arising independently of tumor invasion, metastasis or treatment-related consequences. PNS are caused by an autoimmune response, producing onconeural antibodies against neural antigens expressed by multiple distinct tumors, associated with several neurologic syndromes. Anti-Ma2 is an onconeural antibody found in PNS patients with testicular tumors among others, most often presenting with limbic, brain stem and/or hypothalamic encephalitis.

Case:

 A 40-year-old male presented with testicular swelling associated with progressive paresthesia on  hands and feet, lower extremity weakness, worsening gait, and diplopia. Ultrasound and orchiectomy confirmed a mixed germ cell testicular tumor (50% embryonal carcinoma, 50% teratoma) while brain and spinal magnetic resonance imaging (MRI) revealed findings consistent with limbic encephalitis and myelitis. Cerebrospinal fluid (CSF) analysis showed positivity for anti-Ma2 antibodies, elevated protein (122 mg/dL) and lymphocyte count (99 cells/µL) with a negative culture and gram stain, supporting the diagnosis of paraneoplastic neurologic syndrome secondary to the testicular tumor. Management was immunotherapy with intravenous immunoglobulin (IVIG) and methylprednisolone; however, progressive hyporeflexia, weakness and gait disturbance persisted leading to the suspicion of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), confirmed via electromyography (EMG). Treatment with cyclophosphamide led to temporary improvement but with further deterioration, IVIG, steroids, and mycophenolate mofetil were initiated, stabilizing his condition. Despite improvements in MRI, significant motor and sensory deficits persist.

While CIDP shares immunological features with PNS, there are no documented cases of Anti-Ma2-associated limbic encephalitis, myelitis, and CIDP in a patient with mixed germ cell testicular tumor, emphasizing the need for further study into a potential relationship between CIDP and anti-Ma2, or the central and peripheral nervous system involvement in anti-Ma2-associated PNS.