Recombinant immunoblot for assessment of intrathecally synthesised paraneoplastic antineuronal antibodies in cerebrospinal fluid from patients with paraneoplastic neurological syndromes

Background: Beside of pathophysiological interest, estimation of intrathecal synthesis (IS) of paraneoplastic antineuronal antibodies may increase the diagnostic sensitivity in rare cases of patients with clinically suggestive paraneoplastic neurological syndromes (PNS) and negative or uncertain results in serum. Detection of antigen-specific oligoclonal bands (OCB) in CSF seems to be the most sensitive marker of IS. However, this technique is not suitable for routine laboratory testing.

Patients and methods: This study evaluates the suitability of a commercial immunoblot (ravo PNS-blot) employing recombinant paraneoplastic antigens for estimation of a specific IS of antineuronal antibodies. The immunoblot was evaluated in comparison with the semi-quantitative antigen-specific antibody index (AI) provided by an in-house ELISA.

19 paired cerebrospinal fluid (CSF) and serum samples from patients with different PNS harbouring a variety of antineuronal antibodies (5 anti-HuD, 5 Yo, 4 Ri, 3 CV2/CRMP5, 1 amphiphysin and 1 PNMA2/Ma2) were adjusted to equal concentrations of total IgG and investigated non-quantitatively for specific IS. We compared the results of the immunoblot with the presence of antigen-specific OCB, which were available from 12/19 patients.

Results: Results of the ravo PNS-blot and ELISA correspond in 18/19 patients providing a strong agreement of both techniques. IS according to the results of the ravo PNS-blot was present in samples from 13/19 patients and 14/19 patients in the ELISA, respectively.

All patients with evidence of antigen-specific IS in the ravo PNS-blot had also antigen-specific OCB (specific OCB were not available from 1 patient). Interestingly, total IgG OCB/elevated IgG-index (>0.8) were detected only in samples from 9/13 patients, who all presented with antigen-specific IS according the immunoblot.

However, CSF from 2 patients harboured total IgG OCB, while the ravo PNS-blot did not show antigen-specific IS. In one of these patients also low antigen-specific AI as well as stronger antigen-specific OCB in serum compared to CSF argued against specific IS.

Conclusion: Our results suggest a similar ability in detection of IS using the ravo PNS-blot compared to antigen-specific OCB and a higher suitability in comparison with total IgG OCB/IgG-index provided by routine laboratory testing. Thus, the ravo PNS-blot seems to be suitable for non-quantitative estimation of IS of specific paraneoplastic antineuronal antibodies in PNS.