Neurological Disorders: Small Fiber Neuropathy

Introduction

Small Fiber Neuropathy, as the name implies is a type of neuropathy where the small diameter nerve fibers are affected by disease processes.

Neuropathy means diseases or damage to peripheral nerves. These nerves are made of two types of nerve fibers; large and small diameter fibers. Please click on Neuropathy for additional details on this condition.

The small nerve fibers are non myelinated or scantily myelinated and conduct nerve impulses slowly. Pain, temperature and autonomic nerve impulses are carried by these small fibers, so autonomic neuropathy is also a type of small fiber neuropathy.

Clinical Presentation

The following manifestations are common;

• Pain
• Burning sensation
• Loss of pain and/or temperature sensation over the skin or mucosal membrane
• Autonomic changes like abnormal heart rate blood pressure, orthostatic hypotension, skin changes, impotence, bladder and or bowel incontinence or retention etc

What are the causes?

The following are some of the common causes;

• Diabetes
• Porphyria
• Fabry disease
• Paraneoplastic conditions
• Connective tissue disorders(autoimmune disorders)
• Amyloidosis etc

Please note that both small & large fiber neuropathies may coexist, and in fact several conditions trigger both types of neuropathies together because both small & large fibers are damaged.

Diagnosis

The routine EMG/NCS (electromyography/nerve conduction studies) will not pick up this condition, it only picks up large diameter neuropathy. Special tests are available for detection of small fiber-neuropathy that includes skin punch biopsy and estimation of epidermal small diameter fiber density, autonomic neuropathy tests (indirect way of diagnosing).

Once this type of neuropathy is diagnosed then investigations are done to look for what caused it. Such tests include blood sugar, workup for connective tissue disorders, tumor work up, tests to look for porphyrias, amyloidsis etc.

Management

If a treatable cause is identified then it is treated accordingly. Although whatever damage has happened cannot be always reverted, however if treatment is initiated early further damage can be prevented.

Pills like duloxetne, gabapentin etc help symptomatically by alleviating the nerve pain.

Autonomic dysfunction is treated appropriately.

A neurologist is commonly involved in the care of patients with this type of neuropathy.

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