Diabetic peripheral neuropathy: How reliable is a homemade 1-g monofilament for screening?

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Original Research

Diabetic peripheral neuropathy: How reliable is a homemade 1-g monofilament for screening?

J Fam Pract. 2006 June;55(6):505-508

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References

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Conclusions

The 10-g monofilament is not as sensitive as the 1-g filament, VDT, or the fully quantitative pressure threshold for detecting neuropathy. It is, however, highly specific (99.3%). The 1-g monofilament has nearly the same specificity (96.3%), but has about 10% higher sensitivity at 52.4%. These results support the notion that the 1-g monofilament offers a more sensitive screening tool for diabetic neuropathy than the 10-g filament, without sacrificing specificity.

The use of single monofilaments tested at a single site yielded similar results as a number of other studies that examined multiple testing sites. Studies found that combination tests (2 sites combined) yielded a PPV of only 84%,¹⁵ whereas our results with the same 10-g filament at a single site yielded a PPV of 98%, and the 1-gram filament further improved sensitivity with a PPV of 94%.

FAST TRACK

Be sure to measure and confirm the buckling force of homemade filaments

Some methodological issues are potential sources of error in this study. We constructed filaments with readily available materials and a standardized method. Therefore, we were able to produce large quantities of inexpensive and disposable monofilaments. Studies have shown that the actual buckling force of commercially supplied filaments can vary considerably.¹⁶ Therefore, especially with fishing line, be sure to measure and confirm buckling force. Using our technique, we were able to consistently validate the buckling force of each filament.

Furthermore, monofilaments age and lose their compressible strength with repeated use. Our method eliminated this drawback by creating disposable, single-use monofilaments.

In addition, the experience of Litzelman and colleagues¹⁷ indicates that giving patients monofilaments encourages self examination, engenders behavioral change, and reduces ulcer rate by almost 60%.

FAST TRACK

Patient self-examination with monofilaments reduces ulcer rate by nearly 60%

In summary, we found that a single homemade monofilament using fishing line has considerable clinical utility. It is an economical, quick, and simple test to perform at the bedside or even in the field. The 1-g filament is considerably more sensitive than the commonly used 10-g version without sacrificing specificity. Both can be constructed from 25-lb fishing line cut to 8- or 4-cm, respectively. For these reasons we recommend its use as a screening tool for physicians, health care providers, and patients in detecting diabetic neuropathy. We do not, however, recommend that the monofilament be used as a substitute for quantitative tests for vibration and pressure,^18,19 both of which are sensitive to early and milder changes in sensory function.

CORRESPONDENCE
Aaron I. Vinik, MD, PhD, Eastern Virginia Medical School, Strelitz Diabetes Institutes 855 W. Brambleton Avenue, Norfolk, VA 23510. E-mail: vinikai@evms.edu