eNeuro

Data reveal the best screening tests for polyneuropathy

Tracy Sax, M.D.

General neurologist, peripheral nerve disorders
Providence Portland Medical Center
The Oregon Clinic

Peripheral neuropathy, or chronic distal symmetric polyneuropathy, is a common disorder encountered by neurologists and primary care physicians. The prevalence of polyneuropathy in the general population is estimated to be 2 to 7 percent, with prevalence approaching 8 percent in people 55 and older.

The disorder can be caused by many potentially treatable etiologies; however, up to one-third of patients may have normal laboratory testing and are ultimately diagnosed with idiopathic neuropathy.

Prior to the practice parameter jointly published by the American Academy of Neurology, American Association of Neuromuscular and Electrodiagnostic Medicine, and the American Academy of Physical Medicine and Rehabilitation in January 2009, there were no recent, evidenced-based guidelines for laboratory testing for the evaluation of polyneuropathy.

In our practice within The Oregon Clinic, there were great variations in the number of blood tests performed for this diagnosis, and no clear selection of tests ordered.

We received feedback from the primary care community that our group ordered many blood tests for the workup of polyneuropathy that had low diagnostic yield. I submitted a grant to the Interhospital Physicians Association to review this systematically.

How the study was conducted

Charts, lab data and electrophysiologic tests from patients presenting to The Oregon Clinic neurology with a diagnosis of idiopathic polyneuropathy were reviewed from Jan. 1, 2007, to June 30, 2008.

The diagnosis code of 356.4 (idiopathic neuropathy) was used to identify these patients. Providence Medicare patients were selected for this study based on easier identification of blood testing through Providence Portal.

All blood testing pertaining to the time period of the initial evaluation of patients by members of our group for this diagnosis code was analyzed and recorded. Between Jan. 1, 2007, and June 30, 2008, a total of 120 Providence Medicare patients with the diagnosis of idiopathic polyneuropathy were seen in our outpatient neurology clinic. All patients had laboratory testing performed at the time of the visit or prior to the consultation.

Of the patients reviewed in this study, 48 percent had normal blood tests and were diagnosed with idiopathic neuropathy. Yet the study also found that:

• Fourteen patients (12 percent) were felt to have a diabetic neuropathy.
• Eight patients (7 percent) were diagnosed with glucose intolerance as a cause for their neuropathy.
• Twelve patients (10.5 percent) were diagnosed with monoclonal gammopathy of uncertain significance, or MGUS.
• Fifteen patients (13 percent) were felt to have a toxic neuropathy from medication, chemotherapy or heavy alcohol use.
• Thirteen patients (11 percent) had abnormal thyroid tests. Based on chart review, however, this was not necessarily felt to be the cause of their neuropathy.
• Three patients (2.6 percent) were identified with a probable hereditary neuropathy based on nerve test data, history and examination.
• Three patients (2.6 percent) were diagnosed with B12 deficiency as a cause for their neuropathy, based on abnormal methylmalonic acid levels. No patient had an abnormal B12 level.
• An inflammatory cause was found in four patients (4 percent, one with presumed Sjogren’s disease and the others with chronic inflammatory demyelinating neuropathy, or CIDP).
• Five (4 percent) were diagnosed with either post-polio syndrome or amyotrophic lateral sclerosis.

Results and recommendations

This study found a low diagnostic yield for many laboratory investigations in the diagnosis of chronic polyneuropathy. The most common laboratory abnormality in this study related to glucose metabolism.

The data from this study also confirm that glucose tolerance testing is associated with the highest diagnostic yield, but was tested in only 28 patients (25 percent). Many tests that had been routinely ordered in the past – ANA, RPR and heavy-metal screens – are no longer routinely recommended by the AAN, AANEM and AAPMR in the initial screening evaluation of chronic polyneuropathy.

In accordance with the recently published practice guideline, I would recommend checking CMP, CBC, glucose tolerance test, TSH, MMA, SPEP/UPEP and IFE as initial screening tests. Further laboratory studies may be warranted in specific situations based on nerve conduction study results or patient history, but should not be routinely ordered.