First reports on the association of lung cancer, cerebellar degeneration and myasthenic symptoms date back to the 1970s [
111]. A role of antibodies to VGCC in patients with PCD was first suggested by Clouston et al., who reported three PCD patients with SCLC, small-cell prostate cancer or non-Hodgkin lymphoma, respectively, two of whom had in addition LEMS [
112]. Shortly after, Lennon et al. reported both P/Q- and N-type VGCC antibodies in an independent cohort [
113]; however, no detailed data on the frequency among the various underlying tumours were provided, and almost all of the PCD patients included (
n = 34) had additional anti-neuronal antibodies. In a third study, which comprised only patients with small-cell lung cancer (SCLC) and PCD, anti-P/Q-type VGCC autoantibodies were detected in 12/50 cases (24 %) using a
125I-ω-conotoxin MVIIC-based assay, including all patients with signs or symptoms of LEMS but also five PCD patients without LEMS [
114]. By contrast, only 1 of 49 control patients with SCLC but no paraneoplastic CNS syndrome had P/Q-type VGCC antibodies. Similarly, antibodies to N-type VGCC were detected in the same study using a
125I-ω-conotoxin GVIA-based radioimmunoprecipitation assay (RIA) in 9/50 samples from SCLC-PCD patients, six of whom (66 %) had no LEMS at the time of testing. Voltz et al. [
115] used a commercial RIA based on
125I-ω-conotoxin MVIIC to detect anti-VGCC in eight out of 66 patients with SCLC and anti-Hu syndrome. Of these eight patients, two had PCD without LEMS and two PCD with LEMS. Of note, none of 27 patients with PCD and tumours other than SCLC was positive for P/Q-type VGCC antibodies. By contrast, P/Q VGCC antibodies were absent in a smaller series of anti-Yo-positive patients with gynaecological tumours [
116]. Graus et al. examined PCD patients with lung cancer with or without anti-Hu antibodies (23 %) but with no symptoms beyond the cerebellum for anti-P/Q-type VGCC, again using a
125I-ω-conotoxin MVIIC assay, and detected raised levels in 16 (41 %) of 39 patients with positive PCD, 9 of whom did not have clinical or subclinical LEMS (56 %) and 14 of whom were negative for anti-Hu [
109]. The median time between onset of PCD and tumour diagnosis was 3 months. The most frequent lung tumour diagnosis was SCLC; only two patients had NSCLC. Except for the prevalence of LEMS, no relevant differences were observed between PCD patients with and without VGCC antibodies. The authors concluded that anti-P/Q-type VGCC could be a more sensitive marker for PCD than anti-Hu and in general a useful marker for lung cancer-associated PCD.
However, anti-VGCC autoantibodies are not always associated with cancer in patients with cerebellar ataxia. Clouston et al., in their original series on anti-VGCC in ataxia patients, reported two non-paraneoplastic cases [
112], and Bürk et al. found P/Q-type VGCC-specific antibodies in 8/67 (12 %) of patients with non-paraneoplastic chronic cerebellar degeneration; by contrast, sera from 117 control patients were negative in the latter study [
110].