The diagnostic challenge of small fibre neuropathy: clinical presentations, evaluations, and causes.

Small fibre neuropathies are a heterogeneous group of disorders affecting thinly myelinated Aδ-fibres and unmyelinated C-fibres. Although multiple causes of small nerve fibre degeneration have been reported, including via genetic mutations, the cause of small fibre neuropathy remains unknown in up to 50% of cases. The typical clinical presentation of small fibre neuropathy is that of a symmetrical, length-dependent polyneuropathy associated with sensory or autonomic symptoms. More rarely, the clinical presentation is characterised by non-length-dependent, focal, or multifocal symptoms. The diagnostic tests to identify small fibre neuropathy include skin biopsy, quantitative sensory, and autonomic testing. Additional tests, such as those measuring small fibre-related evoked potentials and corneal confocal microscopy, might contribute to a better understanding of these neuropathies. Biochemical markers can also help in screening patients for the presence of small fibre neuropathy and to assess disease progression.