Detection of small-fiber neuropathy by sudomotor testing

Victoria A. Low, Paola Sandroni, Robert D. Fealey, Phillip A. Low

Research output: Contribution to journalArticlepeer-review

175 Scopus citations


The symptoms of burning sensation affecting the feet, thought to be due to a distal small-fiber neuropathy (DSFN) affecting somatic unmyelinated fibers, are usually accompanied by vasomotor or sudomotor changes suggestive of involvement of autonomic fibers. We therefore examined the relationship between pattern of anhidrosis and DSFN and its etiology, comparing patients with "pure" DSFN (with normal nerve conduction) to those with clinical DSFN (minor conduction abnormalities). We reviewed 125 cases with a clinical phenotype of DSFN. These patients had distal burning discomfort, variable sensory deficits, and intact motor function. All had undergone assessment with thermoregulatory sweat test (TST), autonomic reflex screen (ARS), and nerve conduction studies and electromyography (NCS/EMG). TST showed a distal pattern of anhidrosis in 74%. The quantitative sudomotor axon reflex test (QSART) was abnormal in 74%, with 80% of those having a length-dependent pattern of anhidrosis/hypohidrosis. In total, 93% of patients had a distal pattern of abnormality on QSART or TST. The Composite Autonomic Severity Score (CASS) was used to quantify the severity and distribution of autonomic deficits: 98% had CASS abnormality (sudomotor, 98%; adrenergic, 43%; cardiovagal, 35%). EMG was normal or showed unrelated abnormalities in 75%. The most common etiologies of DSFN were idiopathic (73%), presumed hereditary (18%), and diabetes (10%). Sudomotor examination is thus a highly sensitive detection tool in DSFN. Autonomic involvement is mainly distal, and additionally may involve adrenergic and the long cardiovagal fibers.

Original languageEnglish (US)
Pages (from-to)57-61
Number of pages5
JournalMuscle and Nerve
Issue number1
StatePublished - Jul 2006


  • Anhidrosis
  • Composite Autonomic Severity Score (CASS)
  • Distal small-fiber neuropathy (DSFN)
  • Quantitative sudomotor axon reflex test (QSART)
  • Thermoregulatory sweat test (TST)

ASJC Scopus subject areas

  • Physiology
  • Clinical Neurology
  • Cellular and Molecular Neuroscience
  • Physiology (medical)


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