To identify the causes of polyneuritis syndrome, we excluded endocrine diseases [normal indicators of insulin, proinsulin, glycated HbA1c, adrenocorticotropic hormone, thyroid-stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4)], infections (cytomegalovirus, Epstein–Barr virus, herpes, and borreliosis), and dysmetabolic origins (vitamin levels for B1, B6, B12, and homocysteine were normal; and amyloid deposition in the subcutaneous fat was absent). Here, INS is linked to infection.