| Summary: | <p>Abstract</p> <p>Objective</p> <p>The purpose of this paper is to report a patient with otherwise unexplained cerebellar ataxia with serum antibodies against contactin-associated protein-2 (CASPR-2) and provide a detailed description of the composition of cellular infiltrates in the cerebrospinal fluid (CSF) compared to the peripheral blood (PB). CASPR-2 antibodies strongly labeling axons of cerebellar granule neurons have recently been identified in sera from nine patients with otherwise unexplained progressive cerebellar ataxia with mild to severe cerebellar atrophy.</p> <p>Design</p> <p>This is a report of a single case.</p> <p>Methods</p> <p>The study methods used were neurologic examination, magnetic resonance imaging, fluorodeoxyglucose positron emisson tomography, lumbar puncture and multicolor flow-cytometry.</p> <p>Results</p> <p>A 23-year-old Caucasian male presented with a two-year history of a progressive cerebellar and brainstem syndrome. Magnetic resonance imaging (MRI) showed pronounced cerebellar atrophy, especially of the medial parts of the hemispheres and the vermis. Cerebral fluorodeoxyglucose positron emission tomography (FDG-PET) showed pronounced hypometabolism of the whole cerebellum. CASPR-2 antibodies were detected in the serum but not the CSF, and none of the staging and laboratory assessments revealed other causes of progressive cerebellar degeneration. Interestingly, flow-cytometry of the CSF as compared to the PB showed increased fractions of CD138<sup>+</sup> plasma cells as well as human leukocyte antigen (HLA)-DR<sup>+</sup> CD8<sup>+</sup> T cells suggesting that both B cells and CD8<sup>+</sup> T cells were preferentially recruited to and activated within the CSF- (and putatively central nervous system (CNS)-) compartment.</p> <p>Conclusion</p> <p>We confirm the association of CASPR-2 serum antibodies with cerebellar ataxia and provide the first evidence for a combined humoral and cellular immune response in this novel antibody-associated inflammatory CNS disease.</p>
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