Double trouble: para-neoplastic anti-PCA-2 and CRMP-5-mediated small fibre neuropathy followed by chorea associated with small cell lung cancer and evolving radiological features

Patients with Purkinje cell cytoplasmic autoantibody type 2 (PCA-2) and collapsin response-mediator protein-5 (CRMP-5) autoantibody can present with multifocal elements of encephalomyeloneuropathy. Except for an anecdotal report, case descriptions of paraneoplastic small fibre neuropathy are lacking. We report paraneoplastic small fibre neuropathy followed by chorea associated with small cell lung cancer. A man aged 57 years with a 35 pack-year smoking history presented with painless subacute paresthesia and weight fluctuation. A non-length-dependent small fibre neuropathy was confirmed by skin biopsy. Further testing revealed positive serum PCA-2 and CRMP-5 autoantibodies, which after positron emission tomography-CT led to histological confirmation of a small cell lung cancer. Initially, abnormal MRI and cerebrospinal fluid studies suggested central nervous system (CNS) involvement which was subclinical; however, 6 months later during antitumour therapy, the patient became symptomatic with choreoathetosis. After combined chemoradiation as well as immunosuppressive and symptomatic therapies, the clinical course stabilised, although residual neurological deficits remained at follow-up a year later. Coexistent PCA-2 and CRMP-5 autoantibodies may occur in the setting of small fibre peripheral neuropathy and choreoathetosis and predict cancer type. Two paraneoplastic syndromes can present successively over months; subclinical CNS involvement with evolving basal ganglia abnormalities can be a paraneoplastic manifestation. In the appropriate clinical setting, paraneoplastic testing should be considered in patients presenting with small fibre neuropathy.