Rho-associated protein kinase 2 (ROCK2): a new target of autoimmunity in paraneoplastic encephalitis.

Onconeural antibodies are associated with cancer and paraneoplastic encephalitis. While their pathogenic role is still largely unknown, their high diagnostic value is undisputed. In this study we describe the discovery of a novel target of autoimmunity in an index case of paraneoplastic encephalitis associated with urogenital cancer.A 75-year-old man with a history of invasive bladder carcinoma 6 years ago with multiple recurrences and a newly discovered renal cell carcinoma presented with seizures and progressive cognitive decline followed by super-refractory status epilepticus. Clinical and ancillary findings including brain biopsy suggested paraneoplastic encephalitis. Immunohistochemistry of the brain biopsy was used to characterize the inflammatory response. Indirect immunofluorescence assay (IFA) was used for autoantibody screening. The autoantigen was identified by histo-immunoprecipitation and mass spectrometry and was validated by expressing the recombinant antigen in HEK293 cells and neutralization tests. Sera from 125 control patients were screened using IFA to test for the novel autoantibodies.IFA analysis of serum revealed a novel autoantibody against brain tissue. An intracellular enzyme, Rho-associated protein kinase 2 (ROCK2), was identified as target-antigen. ROCK2 was expressed in affected brain tissue and archival bladder tumor samples of this patient. Brain histopathology revealed appositions of cytotoxic CD8+ T cells on ROCK2-positive neurons. ROCK2 antibodies were not found in the sera of 20 patients with bladder cancer and 17 with renal cancer, both without neurological symptoms, 49 healthy controls, and 39 patients with other antineuronal autoantibodies. In conclusion, novel onconeural antibodies targeting ROCK2 are associated with paraneoplastic encephalitis and should be screened for when paraneoplastic neurological syndromes, especially in patients with urogenital cancers, occur.

A case of acute paraneoplastic neurological syndrome in BRAF mutant metastatic melanoma.

A 58-year-old man with indolent metastatic BRAF mutant melanoma presented with several days' history of progressive ataxia and dysdiadochokinesia. His PET/computed tomography restaging scan indicated two new fluorine-18-fluorodeoxyglucose-avid mesenteric lymph nodes. Meanwhile, his MRI brain and whole spine were within normal limits. A lumbar puncture indicated an elevated protein level with a normal cell count and negative paraneoplastic antibodies. Because of the lack of an alternative differential, the diagnosis of paraneoplastic syndrome was made. He was started on high-dose corticosteroids as well as dabrafenib and trametinib. Despite this, his neurological symptoms continued to progress. Consequently, he was trialed on a course of intravenous immunoglobulin, which stabilized his symptoms. He continued to improve over several weeks, with near-complete resolution of all his neurological symptoms, and showed a complete radiological response of his disease. To our knowledge, this is the first reported case of paraneoplastic neurological syndrome with mixed neurology associated with BRAF mutant cutaneous melanoma that responded to BRAF targeted therapy.