"Peripheral neuropathy is a common problem that often prompts a lengthy and expensive diagnostic evaluation," write A. Gordon Smith, MD, and J. Robinson Singleton, MD, from the University of Utah School of Medicine in Salt Lake City. "A rational, evidence-based diagnostic approach to peripheral neuropathy is desirable.... The goal was to develop a focused diagnostic algorithm that can be easily applied in a general medical setting."

Using a standard diagnostic approach, the authors evaluated 138 patients referred with predominantly sensory symptoms and no previously defined etiology for neuropathy.

Family history was positive in 25% of patients, with at least one first-degree relative with symptoms suggesting neuropathy. The two-hour oral glucose tolerance test (OGTT) had the highest diagnostic yield (61%) of all laboratory tests and was more sensitive than other measures of glucose metabolism. Two patients were diagnosed with vitamin B12 deficiency.

Based on these findings, the authors suggest that patients with sensory-predominant neuropathy should be tested for glucose tolerance and vitamin B12 level, that abnormalities of serum protein electrophoresis and antinuclear antibodies are of uncertain significance, and that other tests should be performed only when the clinical scenario is suggestive.

"Using this approach, only 31% of patients completing the recommended evaluation were found to have an idiopathic neuropathy," the authors write. "Patients with atypical features may benefit from referral to a peripheral neuropathy center."

Since the manuscript was accepted for publication, the American Diabetes Association (ADA) revised its criterion for impaired fasting glucose (IFG) as ranging from 100 to 125 mg/dL (5.6 - 6.9 mmol/L). Of an additional 12 patients with IFG using the new criterion, seven had impaired glucose tolerance (IGT) and two had diabetes on the basis of the two-hour plasma glucose test during an OGTT.

"The revised criterion has not substantially altered the diagnostic yield of the fasting plasma glucose test (either alone or as part of the OGTT) in this patient population," the authors write.

From the results of the study, it was concluded that routine use of OGTT is recommended to screen patients presenting with sensory-predominant neuropathy. Also, routine measurement of vitamin B12 levels is warranted, and those with borderline levels should have serum concentrations of methylmalonic acid and homocysteine measured.