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Small fibre neuropathy (SFN) is a neuropathy selectively involving the small diameter myelinated and unmelinated nerve fibres (Group C nerve fiber). It is also called small fiber neuropathy (American), small fibre peripheral neuropathy, small fiber sensory neuropathy (SFSN), and C fiber neuropathy. Aetiology of SFN includes most frequently diabetes or pre-diabetes status and immune-mediated diseases though it remains frequently unknown (referred to as idiopathic SFN). The diagnostic criteria have not been fully defined but as of 2008 a new "Gold-Standard" for clinical practice and research has been proposed. The basis of this standard relies on a skin biopsy which requires taking a small punch of skin at both the calf and thigh under local anesthetic. Previously most diagnosis were based on the elimination of all other options. Unless an identifiable cause is found (and treated) the management of SFN usually centres upon symptomatic treatment of neuropathic pain and fatigue. Treatment options are limited. In idiopathic SFN spontaneous remission of neuropathic pain is possible but is the exception rather than the rule (10% at 2 year follow up)

Clinical Features & Presentation
SFN usually manifests as a length dependent process with the feet initially affected. If the condition worsens the symptoms spread proximally as shorter axons become affected. The hands become symptomatic at about the same time as leg symptoms ascend to mid calf. This is the text book presentation known as "Stocking and Glove Distribution". However a multitude of presentations have been noted. As shorter fibres become damaged symptoms can affect the face and head.

SFN is categorized based on the function of the nerve fibres involved. and based on the size of the fibres and velocity at which they conduct nerve signals.

Nerves can be broken into three groups depending on the functions they perform;

1. nerves with motor function including contracting and relaxing muscles and performing certain specified functions 2. nerves with sensory function including sensations for touch, vibration, temperature and pain. 3. nerves with autonomic function including sweating, bowel movements, penile functions, blood pressure and heart rate variability.

Based on size and conduction velocity three types of nerve fibre can be distinguished, large diameter myelinated (Aß-), small diameter myelinated (Ad-) and unmyelinated (C-) nerve fibers can be distinguished. Aß-fibers carry motor functions as well as vibration sense and touch. Ad-fibers carry cold sensation and C-fibers carry warmth sensation. Pain and autonomic functions are mixed Ad- and C-fiber functions.

Based on size and conduction velocity, large diameter myelinated (Aß-) nerve fibres (Type_II_sensory_fiber), which carry motor functions as well as vibration sense and touch, small diameter myelinated (Ad-) nerve fibres which carry cold sensation and unmyelinated (C-) nerve fibers which carry warmth sensation.

Pain and autonomic functions are mixed Ad- and C-fiber functions. Small fiber neuropathies (SFN) preferentially affect small-diameter myelinated and unmyelinated fibers, leaving the larger myelinated fibers relatively unaffected. (i.e. Motor functions and deep tendon reflexs are not affected)

Affected patients typically present with spontaneous neuropathic pain and reduced thermal and pain sensitivity but with normal strength, propioception, and reflexes.

1,2 SFN has been primarily considered as a type of somatic neuropathy, but thin myelinated and unmyelinated fibers are responsible not only for temperature and pain perception but also for autonomic function.3 Therefore, beside the neuropathic pain, patients with SFN may complain of symptoms related to autonomic dysfunction.

Small fiber neuropathies (SFN) preferentially affect small-calibre myelinated and unmyelinated fibers, leaving the larger myelinated fibers relatively unaffected. Affected patients typically present with spontaneous neuropathic pain and reduced thermal and pain sensitivity but with normal strength, propioception, and reflexes.1,2 SFN has been primarily considered as a type of somatic neuropathy, but thin myelinated and unmyelinated fibers are responsible not only for temperature and pain perception but also for autonomic function.3 Therefore, beside the neuropathic pain, patients with SFN may complain of symptoms related to autonomic dysfunction.