Double Vision? - Give Your Head a Shake

54-year old man with sub-acute progressive cerebellar disease. Clinical testing suggested left vestibulocerebellear dysfunction vs. irritative right brain stem lesion, presenting with a right beating nystagmus, ataxia, and left hypertropia. Enhanced posterior fossa MRI showed an absence of structural lesion. Blood work included B12, vitamin E, and TSH of which all were normal. CSF with cytology normal. Paraneoplastic syndrome was quickly entertained. Auto-antibody testing revealed CRMP-5 positivity. CT chest, abdomen and pelvis normal. A scrotal ultrasound revealed 2 suspicious lesions in the right testicle. Complete orchiectomy was performed and pathology showed characteristic features of a regressed testicular cancer. 4,5, Treated with IVIG with relative disease stability, with mild progression of cerebellar syndrome. Repeat whole body imaging was negative. Over several months, horizontal head shaking nystagmus, although initially right beating, evolved into upbeat nystagmus following horizontal shaking indicative of central cross coupling as part of his peripheral to central progression. Nystagmus well controlled with 4-aminopyridine. Most patients with CRMP-5 paraneoplastic syndromes present with peripheral neuropathy, or movement disorders. Optic neuropathy is the predominant neuro-ophthalmologic presentation; however, has been described in association with PCD. 2 CRMP-5 is most commonly described in association with small cell lung cancer, and thymoma, 2 and one previous report of testicular CA presenting with limbic encephalitis and choreiform dyskinesis. 1 To our knowledge, our case represents the first to report PCD in association with testicular cancer and CRMP-5 autoantibodies. Although precise differentiation between a left fourth nerve palsy and cerebellar-origin skew deviation was difficult due to conflicting clinical findings, objective excyclotorsion of the lower eye and incyclotorsion of the higher eye was documented, making skew more plausible, in particular given the associated vestibulocerebellar findings.