Commentary: Paraneoplastic Syndrome Associated with Kelch‐Like Protein 11 Antibodies Presenting with Progressive Ataxia and Tremor

With the exception of ocular involvement, the case shows the typical features of a pancerebellar syndrome with dysmetria, vertigo, and axial ataxia (scanned speech and impaired tandem gait).1 In this context, tremor can be classified as “intention” type, according to the recent classification. The occurrence of lip tremor is, however, uncommon, while the head tremor (not visible in the video) can represent a yes-yes type called “titubation.” The positive but unspecific effect of alcohol and the therapeutic attempt with propranolol might indicate a possible diagnosis of essential tremor (ET)-plus. However, ET is an axis-1 diagnosis, which should be reconsidered as soon as an etiology is found. More important, although subtle cerebellar features are possible in ET, cerebellar speech is not characteristic. A confounding aspect is patient's longstanding clumsiness, possibly related to a likely congenital small arachnoid cyst of the posterior fossa.1 The lack of family history of ataxia, the presence of oligoclonal bands, and the progressive atrophy of the cerebellum over a short timeframe are important diagnostic clues, raising autoimmunity, possibly paraneoplastic (given the history of seminoma), as the most probable cause. Several antibodies associate with a pure cerebellar syndrome (eg, anti-GAD65, VGCC, mGluR1, DNER, Sox1, Zic4) including some detected in testicular cancer, although rarely (Ma2). Recently, Kelch-like protein-11 antibodies have been discovered in young men with seminoma, who—interestingly—also featured vertigo as 1 of the presenting signs in roughly 60%.2, 3 Numerous (often >8) unmatched oligoclonal bands may be another pointer to the diagnosis.2, 3 We can only speculate why the neurological syndrome developed several years afterward without evidence of seminoma recurrence. It may be that the immunological response eliminated the tumor or that the immune reaction has become independent of the initial trigger, possibly precipitated by other mechanisms. As in this case, the response to immunotherapy is mixed.2, 3 (1) Research Project: A. Conception, B. Organization, C. Execution; (2) Manuscript Preparation: A. Writing of the First Draft, B. Review and Critique. A.F.: 1A, 1B, 1C, 2A P.P.: 2B I.O.B.: 2B B.B.: 1A, 1B, 1C, 2B The authors confirm that neither informed patient consent nor the approval of an institutional review board was necessary for this work. We confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this work is consistent with those guidelines. No IRB approval was required for this work. There was no specific funding received for this work. The authors declare that there are no conflicts of interest relevant to this work. A.F. is a consultant for Abbott, Inbrain, Ceregate, Medtronic, Boston Scientific, Sunovion, Ipsen, and AbbVie. He has received research support from Abbvie, Medtronic, Boston Scientific, University of Toronto, The Michael J. Fox Foundation for Parkinson's Research, and honoraria for serving as a speaker from UCB, Medtronic, Boston Scientific, AbbVie, Sunovion, and Ipsen. I.O.B. is on the advisory boards of Biogen Inc., Boston Scientific, Accorda, and Amneal Pharmaceuticals and is a consultant for LEK Consulting, Ideo Inc., and Humancraft. P.P. and B.B. have no disclosures.

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