[Small fiber dysfunction in peripheral neuropathies]

Disfunction of thin myelinated and unmyelinated fibers may appear isolated or in association with large-myelinated fibers lesion. Small-fiber neuropathy includes autonomic and sensory symptoms, most prominent of them thermo-algesic deficits.

In some acute neuropathies, small-fiber lesion is relatively pure, as in pandysautonomia, but it also appears in disorders with prominent somatic involvement, such as the Guillain-Barre syndrome, in which case autonomic symptoms worsens the prognosis. Small-fiber dysfunction is important in certain diseases that involve different components of the nervous system, like paraneoplastic syndromes and porphyria. Some drugs and toxic substances may damage thin myelinated and unmyelinated fibers. Nowadays, chronic idiopathic small-fiber neuropathy is diagnosed more frequently, because of the recent development of techniques that selectively evaluate this peripheral nerve component. Hereditary sensory and autonomic neuropathies can also be studied. Small-fiber dysfunction is very prominent in some diseases, e.g. diabetes mellitus and amyloidosis. In the pure autonomic failure, only the peripheral component of the autonomic nervous system is affected, and this feature is the key to make diagnosis versus multisystem atrophy. There are situations in which there is no clear deviation from normality, namely old age autonomic failure and orthostatic intolerance syndrome in which autonomic evaluation is mandatory.