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Non‐paraneoplastic ataxia in a patient with contactin‐associated protein‐2 antibodies and benign course

A 76-year-old man came to our attention reporting an 8-month history of acute onset gait unsteadiness, dysarthria and painless lower limb paresthesias. Disturbances were initially associated with a feeling of lightheadedness on sudden standing and episodes of excessive sweating without other dysautonomic symptoms. Family members reported personality changes, apathy and attention difficulties during long conversations whereas the patient reported only a sensation of ‘fluctuating mental confusion’ during the day. Feelings of lightheadedness improved during the first months of the disease whilst gait and language disturbances worsened during the 2 months before admission. His family history was unremarkable; he was a heavy smoker, with chronic obstructive pulmonary disease and hypertension. Five months before his presentation to our clinic he had successfully undergone surgery for a low grade papillary renal neoplasm. On admission, neurological examination revealed dysarthria, slow saccades, slight limb dysmetria, lower limb hypopallaesthesia and altered joint position sense, positive Romberg sign and gait ataxia. Brain magnetic resonance revealed a slight cortical and cerebellar atrophy with signs of vascular encephalopathy. A nerve conduction study and electromyography disclosed a slight peripheral sensory-motor neuropathy with no evidence of peripheral nerve hyperexcitability whilst somatosensory evoked potentials disclosed dorsal column involvement (Tables 1 and 2). Skin biopsy showed a somatic and autonomic small fiber neuropathy. Cerebrospinal fluid analysis and study of cardiovascular reflexes were unremarkable. Neuropsychological assessment revealed a mild multiple cognitive domain impairment affecting visual memory, constructional apraxia and phonemic verbal fluency. Whilst waiting for serological screening, presuming a diagnosis of autoimmune ataxia due to the concomitant appearance of gait unsteadiness, mild dysautonomic, cognitive and neuropathic symptoms, the patient was discharged on oral steroid therapy (prednisone 50 mg/ day) with an initial disappearance of ‘mental confusion’ and a later improvement of dysarthria and ataxia but without complete remission. The patient signed informed consent for participation in the study. Serological screening for vitamin E, vitamin B12, antibodies anti-GAD, P-ANCA, C-ANCA, ANA, anti-Ro, anti-La, anti-dsDNA, anti-Sm and antiphospholipid, anti-thyroid, anti-SSA/ SSB, anti-tissue transglutaminase, antideamidated gliadin peptide, anti-Hu, anti-Yo, anti-Ri, anti-Tr, anti-GAD, anti-amphyiphysin, anti-CV2/CRMP5, anti-LGI1 and P/Q type voltage-gated calcium-channel antibodies was negative. In contrast, serum testing with radioimmunoprecipitation assay for voltage-gated potassium-channel (VGKC) complex antibodies was positive (241 pmol/l; normal range <100 pmol/l) as were the cell-based assays for contactin-associated protein-2 antibodies (CASPR2).