Anti-Ri-associated paraneoplastic brainstem cerebellar syndrome with coexisting limbic encephalitis in a patient with mixed large cell neuroendocrine lung carcinoma.

Paraneoplastic neurologic syndromes (PNS) can be the first manifestations of occult malignancies. If left untreated, PNS often lead to significant morbidity and mortality. Anti-Ri (anti-neuronal nuclear antibody type 2 [ANNA-2]) autoantibodies are commonly associated with breast and small cell lung cancers. Cases of anti-Ri paraneoplastic cerebellar degeneration are reported, but few describe severe nausea and coexisting limbic encephalitis as the major presenting features. We report a 75-year-old woman with medically-intractable emesis, encephalopathy, diplopia, vertigo, and gait ataxia for 3 months. Examination revealed rotary nystagmus, ocular skew deviation, limb dysmetria, and gait ataxia. After two courses of intravenous immunoglobulin, there was minimal improvement. Anti-Ri antibodies were positive in serum only. CT scan identified a 2.0 cm left lung mass, and histopathology revealed large cell neuroendocrine carcinoma with admixed adenocarcinoma non-small cell lung carcinoma (NCSLC). Though the patient achieved nearly complete clinical recovery after tumor resection, anti-Ri levels remained high at 20 months post-resection. To our knowledge this is the first report of a paraneoplastic brainstem cerebellar syndrome with coexisting limbic encephalitis involving anti-Ri positivity and associated mixed neuroendocrine/NSCLC of the lung with marked improvement after tumor resection.