Paraneoplastic antineuronal antibodies in patients with systemic autoimmune diseases.
Sera from 71 patients with primary Sjögren's syndrome (PSS) and from 102 patients with systemic lupus erythematosus (SLE) were tested by immuno-dot blotting against HuD, Ri, Yo and amphiphysin recombinant proteins. For Ri, Yo and amphiphysin antigens, no immunoreactivity was found in the 173 sera tested. One PSS patient with a clinical picture of subacute sensory neuronopathy had high titers of anti-Hu antibodies. An extensive search for an underlying tumor was initially negative but a small cell lung cancer was eventually discovered three years later. Another patient with SLE and a clinical picture of demyelinating polyradiculoneuropathy had anti-Hu antibodies. Repeated search for an underlying tumor remains negative after five years follow-up in this young non-smoking patient. In addition, the neuropathy progressively improved and the anti-Hu antibodies titer slowly decreased from 1:8000 to 1:2000, making the diagnosis of paraneoplastic syndrome unlikely in this patient. This study indicates that the detection of anti-Hu antibodies in patients with known symptomatic systemic autoimmune diseases such as PSS or SLE should induce the same work-up than the detection of these antibodies in the absence of other immune diseases, i.e. repeated search for occult cancer during several years. As illustrated by our first patient, this strategy may be fruitful. Nevertheless, the clinician should know that anti-Hu antibodies may exceptionally (0.6% in this series) occur in systemic autoimmune disorders with neurological complications, in the absence of an underlying neoplastic disease.