In small-fiber neuropathy there is preferential involvement of the small unmyelinated nerve fibers that mediate pain, temperature sensation, and autonomic function. In the largest prospective series, 81% of neuropathy patients with IGT had exclusively sensory complaints and 92% recognized neuropathic pain as a dominant symptom of their neuropathy. Examination usually reveals normal strength and mild impairment of sensation distally with reflexes often being normal.

Clinical findings include allodynia, deep aching pain, sympathetic vasomotor changes, pallor alternating with rubor, cyanosis, and mottling. “Small fiber” neuropathy is characterized by superficial burning pain in the feet. Singleton MD, in Neurobiology of Disease, 2007 B. Computer-assisted sensory examination for small fiber function is sometimes helpful. QSART shows normal sweat volume in the forearm and anhidrosis in the lower extremities, maximal distally. Most patients with DSFN will have QSART impairment in the feet. An epidermal biopsy to quantitate epidermal fiber density can also be useful. The most sensitive diagnostic test is quantitative sudomotor axon reflex test (QSART) or TST showing distal anhidrosis. Occasionally, the medial plantar sensory action potential is reduced, or minimal motor unit changes or occasional fibrillation potentials are seen. Electromyography and nerve conduction studies are unremarkable. Sensation may be mildly impaired, especially for sharp–dull discrimination and temperature perception. The neurological examination is usually unremarkable. However, a majority of cases of DSFN are idiopathic and run a benign course. Sudomotor dysfunction, commonly manifested as excessive sweating or as anhidrosis, is also common.ĭSFN may occur with diabetes and inherited and immune-mediated neuropathies. Occasionally, rubor, cyanosis, and mottling are present. Sympathetic dysfunction manifests as vasomotor changes, usually pallor. Troublesome allodynia, in which light touch or firm pressure, as with weight bearing, causes pain, is common. The pain is most common in the sole and toe-pads with later involvement of the dorsum. Symptoms include superficial burning and a deeper aching pain. Postganglionic sympathetic impairment occurs without significant somatic neuropathy. Low, in Encyclopedia of the Neurological Sciences (Second Edition), 2014 Distal Small Fiber NeuropathyĭSFN is characterized by distal pain and dysesthesias.

Small pain fiber nerve conduction study