Clinical and differential diagnosis of polyneuropathies - Etiology determines therapy

Knowledge of the etiology of polyneuropathies is essential for any therapeutical decision. In the first step, the distribution of neuropathic symptoms and signs separates focal from generalized neuropathies. The second diagnostic step involves the discrimination of axonal from demyelinating forms to further narrow the etiological spectrum. The diagnostic contribution from laboratory blood tests is commonly overrated. Tests for diabetes, borreliosis and paraproteinemia are a few exceptions. A spinal tap is warranted to further identify (neuro-)borreliosis by pleocytosis, or inflammatory causes by increased CSF protein. Any progressive neuropathy severely interfering with private or professional activities indicates a nerve biopsy to identify immune neuropathies with or without vasculitis because of their specific therapeutic implications.