Do you screen for paraneoplastic antibodies in patients with suspected ALS?

I do not screen ALS patients routinely for PNP antibodies because I do not believe true paraneoplastic ALS exists as a disease entity. The few rare paraneoplastic motor neuron syndromes I am aware of are very different from typical ALS- either a purely UMN syndrome resembling PLS which has been described with breast Ca or purely LMN syndrome which is rarely seen with some lymphomas. Anti Hu can sometimes show prominent motor neuropathy but it is almost never isolated; most patients have concomitant cerebellar ataxia or sensory neuropathy or encephalitis etc. therefore if I see a patient with typical progressive asymmetric limb or bulbar weakness and unequivocal combined UMN and LMN signs at the same level, I will not order those antibodies ...

A 2015 article in research gate described testing 316 patients with MND of which 44% had Mayo paraneoplastic antibody panel done. 13 of the 138 patients tested (9%) had at least 1 paraneoplastic antibody. A 2022 article in Brain Science described a patient with MND with anti SOX1 and anti Gad65 antibodies. No improvement with IVIg. 2 other case had no PNP antibodies but had tumors. The authors suggest screening ALS patients because they might improve or stabilize after immunotherapy. The question is "What % of ALS patients have PNP antibodies and what % of those have a better course (i.e., improvement) with immunotherapy?"! Screening would be the only way to find out. Cost/benefit analysis for screening is needed.