The purpose of this study is to determine the prevalence of patients with a polyneuropathy of undetermined etiology based on the normal results of laboratory data (CRP, glucose, electrolytes, urea,transaminases, TSH, immunoglobulins, vitamin B12, RF, ANA, antibodies against Lyme borrelia) no anamnesis for carcinoma, no continuous alcohol consumption; no light-chain-amyloidosis; no anamnesis for heavy metal exposure.