Small fiber peripheral neuropathy

Small Fiber Peripheral Neuropathy (SFPN) is a type of peripheral neuropathy, a condition affecting the peripheral nervous system, which is the network of nerves outside the brain and spinal cord. SFPN specifically involves the damage to the small unmyelinated C fibers and thinly myelinated Aδ fibers of the peripheral nervous system. These fibers are responsible for carrying pain and temperature sensations from the skin to the brain, as well as for autonomic functions.

Causes

SFPN can be caused by a variety of factors, including diabetes mellitus, autoimmune diseases (such as Sjögren's syndrome, lupus, and rheumatoid arthritis), infections (like HIV), genetic disorders, and exposure to toxins. In some cases, the cause remains idiopathic, meaning it is unknown.

Symptoms

The symptoms of SFPN include pain, often described as burning, tingling, or stabbing, and abnormalities in temperature sensation. Patients may also experience autonomic symptoms such as changes in sweating, bowel, bladder, or cardiovascular functions. The severity and range of symptoms can vary widely among individuals.

Diagnosis

Diagnosis of SFPN involves a combination of clinical evaluation, patient history, and specific tests. These tests may include skin biopsies to evaluate the density of small fibers in the skin, quantitative sensory testing (QST) to assess the function of sensory nerves, and autonomic testing for those with autonomic symptoms. Electromyography (EMG) and nerve conduction studies (NCS), which are commonly used to diagnose other types of peripheral neuropathy, are typically normal in SFPN because they primarily assess larger myelinated fibers.

Treatment

Treatment of SFPN focuses on managing symptoms and addressing the underlying cause if known. Pain management may involve medications such as anticonvulsants (e.g., gabapentin or pregabalin), antidepressants (e.g., duloxetine or amitriptyline), and topical agents. For patients with autonomic symptoms, specific treatments targeting these symptoms may be necessary. Lifestyle modifications, including regular exercise and maintaining a healthy weight, can also help manage symptoms.

Prognosis

The prognosis for individuals with SFPN varies depending on the underlying cause. In cases where the cause can be treated or managed, symptoms may improve or stabilize. However, in idiopathic cases or when the underlying cause cannot be effectively treated, symptoms may progressively worsen over time.