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Tag Archive: 10 gram monofilament

  1. New Study Finds Vibration Testing More Reliable than Monofilament over Plantar Calluses

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    Wynands et al’s recently published “Does plantar skin abrasion affect cutaneous mechanosensation?” brings into focus the importance of plantar callus debridement.  This study measured skin thickness, hardness, monofilament threshold and vibration perception threshold (VPT) in healthy participants over plantar calluses before and after “abrasion” (debridement). The intervention group was compared to a matched control group without callus debridement. Findings included significantly reduced skin thickness and hardness as to be expected after callus debridement. Interestingly, VPTs at 30Hz and 200Hz were not significantly affected by debridement. Monofilament thresholds however were significantly improved after the intervention. This finding led the authors to conclude:

    “Since VPTs are not affected by skin properties, they are likely to be the best choice to analyze sensory deterioration in diabetic feet, where skin property changes could skew data of devices like monofilaments.”

    This recommendation aligns with American Diabetes Association Guidelines for using vibration(large-fiber function) and pinprick/temperature (small-fiber function) testing along with the 10g monofilament when testing for loss of protective sensation (LOPS) in patients with diabetes. Another conclusion drawn from this study is that callus debridement improves light touch perception in healthy study participants. Future studies might evaluate this intervention in patients with varying degrees of diabetic peripheral neuropathy (DPN). Perhaps in addition to reducing pressures on the skin, debridement also will be found to improve skin sensitivity in this at risk group. 

  3. A Week’s Worth of Reasons to Reconsider Monofilament Testing for DPN: Sunday

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    monofilament-sundaySunday: Monofilament testing under ideal conditions assesses light touch by applying pressure to the skin of the foot. Light touch is mediated mostly by large fiber encapsulated nerve receptors and some small nerve fiber mechanoreceptors (see Figure one). For decades, providers have been advised by researchers and expert consensus to accept this as a valid “proxy” test for loss of protective sensation (LOPS)(1). LOPS, more accurately interpreted as a loss of pain sensation, is a small nerve fiber function mediated by specialized free nerve endings known as nociceptors. The obvious question is whether or not a test assessing mostly large fiber nerve function can imply a loss of small fiber nerve function? Although there is thought to be some correlation between the two it is difficult to make a direct comparison. For example, nerve conduction velocity (NCV) testing, acknowledged as the “Gold Standard” for diagnosing neuropathy, tells us nothing about small fiber nerve function.  This lack of direct correlation is heightened in light of recent research demonstrating that small fiber neuropathy (SFN) precedes large fiber neuropathy in the feet of diabetic patients (2).

    Given these facts, the argument can be made that there is an intrinsic flaw in the test itself. Although not commonly discussed in the literature, providers have no doubt seen its impact over the years in the false negatives elicited by the test. The most glaring examples are those patients who will “pass” the monofilament exam while failing to react to a sharp stimulus or complain of pain when presenting with a full-thickness foot ulcer. In these cases, patients most likely are passing the exam with their intact large fiber nerve receptors. Although these may be exceptions, periodic false negatives combined with the errors induced by confounding variables noted in days Monday-Saturday lead one to reconsider the validity of the test as medicine moves into the 21st century. Ultimately providers should consider whether LOPS as diagnosed by the monofilament is effective at further reducing diabetic foot complications.

    nerve-function-graphic2

    Fig. 1. Large and small nerve fiber functions in the skin of the foot. Note that pain perception resides on the small fiber side and light touch is the only shared function.

    1.Boulton, AJ, Armstrong, DG, et al. Comprehensive Foot Examination and Risk Assessment. Diabetes Care 31(8):1679-1685, 2008.

    2. Breiner A, Lovblom LE, Perkins BA, Bril V. Does the prevailing hypothesis that small-fiber dysfunction precedes large-fiber dysfunction apply to type 1diabetic patients? Diabetes Care. 2014 May;37(5):1418-24.

     

  4. A Week’s Worth of Reasons to Reconsider Monofilament Testing for DPN: Saturday

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    monofilament3Saturday: The test provides ambiguous results and poor inter-rater reliability even when done correctly (1). Providers have recently called into question exactly how useful the device is at identifying diabetic patients with LOPS (2).

    1. Collins S, Visscher P, De Vet HC, Zuurmond WW, Perez RS. Reliability of the Semmes Weinstein Monofilaments to measure coetaneous sensibility in the feet of healthy subjects. Disabil Rehabil. 2010;32(24):2019-27.

    2. Dros J, et al: Accuracy of monofilament testing to diagnose peripheral neuropathy:a systematic review. Ann Fam Med 7: 555, 2009.