Monofilament Testing for Diabetic Peripheral Neuropathy

Abstract & Commentary

By Mary Elina Ferris, MD, Clinical Associate Professor, University of Southern California. Dr. Ferris reports no financial relationship to this field of study.

Synopsis: Despite guideline recommendations to utilize monofilaments to detect diabetic peripheral neuropathy, there is a paucity of published literature to support its accuracy.

Source: Dros J, et al. Accuracy of monofilament testing to diagnose peripheral neuropathy: A systematic review. Ann Fam Med 2009;7:555-558.

An extensive medline and embase search without language restrictions was conducted to identify literature support for the diagnostic accuracy of using monofilaments to test for signs of peripheral neuropathy of the feet. Semmes-Weinstein monofilaments are calibrated, single-fiber nylon threads that generate a reproducible buckling stress; different values indicate more stiffness and difficulty in bending. This study focused on the 5.07/10-g monofilament that is the currently recommended filament for use as an indicator for loss of protective sensation in the distal extremities. Of 56 potential articles identified, only 3 survived exclusions for either not using the specified filament, having no reference standard, not being blinded, or being otherwise irrelevant.

The 3 studies included in the final review all involved patients with diabetes, and nerve conduction studies were used as the reference standard to compare accuracy. Sensitivity ranged from 41% to 93%, and specificity from 68% to 100%. The methods for executing the monofilament test were not standardized in the 3 studies. Based on the wide range of results in this review, the authors conclude that monofilament testing should not be used alone to diagnose peripheral neuropathy.

Commentary

It's always interesting to take a step back and question long-accepted beliefs, such as testing for diabetic peripheral neuropathy. In this review, the authors had difficulty even finding standard methods of applying the monofilament and how to interpret the results. Studies where the testers could see visible ulcers or knew the nerve conduction results in advance also had to be rejected for potential bias. Their conclusions about the inaccuracy of monofilament testing confirm other published studies that show poor inter-rater reliability and suggest that a combination of modalities is most effective.1

Ultimately, the best test for peripheral neuropathy is a nerve conduction test, but primary care offices need a reliable screening strategy to identify those who will benefit from this often expensive referral. The American Diabetes Association's 2010 recommendations for comprehensive foot examination include four items: inspection; palpation of dorsalis pedis and posterior tibial pulses; testing for patellar and Achilles reflexes; and determination of proprioception, vibration, and monofilament sensation.2 Clinical judgement is needed to synthesize these results, and the monofilament test alone is insufficient to determine early neuropathy.

References

1. Nather A, et al. Assessment of sensory neuropathy in diabetic patients without diabetic foot problems. J Diabetes Complications 2008;22:126-131.

2. American Diabetes Association. Standards of medical care in diabetes — 2010. Diabetes Care 2010;33(Suppl 1):S11-61.