Timely Neuropathy Testing

A TRIBUTE TO SIDNEY WEINSTEIN Ph.D.

What is the origin of the Semmes-Weinstein Monofilaments? 

Many have asked about the origins of the Semmes-Weinstein Monofilaments. Today what is published in the literature is not always accurate. We owe the modern Nylon threshold test to the vision and foresight of Sidney Weinstein, a neuropsychologist who was one of the first, if not the first, of the neuropsychologists.  For many years in the 1950's Sidney Weinstein worked at Albert Einstein University Hospital in New York. Sidney Weinstein collaborated with Dr. Josephine Semmes, a neurophysiologist at the National Institutes of Health. They used the monofilaments to map cortical areas of the brain in monkeys. The initial publication of normative thresholds in human subjects is found in the now classic book, Somatosensory Changes After Penetrating Brain Wounds in Man (see references).  In personal communication, Dr. Weinstein has explained that his father was interested in materials. Weinstein shared his interests in the discovery of new materials. When DuPoint first invented “Nylon” it was a fascinating unexplored substance. Weinstein recognized its viscoelastic properties as a superior replacement for the progressively sized diameter horsehairs he had been using in sensory threshold testing. Nylon has little humidity absorption, and hair has a lot, a criticism of the horsehair test first described by von Frey in the 1980’s. Sidney Weinstein replaced horsehairs in the von Frey test with Nylon in available diameter sizes, and the test was born. He did not seek to patent his original handle design. He recognized the value of the progressively increasing threshold test in determining normal and abnormal sensory threshold, and wanted this to be able to be shared. Many scholars were interested in sensory testing during this period. Careful examiners from many fields were attempting to gain a better understanding of human sensory physiology. As a point of interest he says he kept the first kits he constructed in a cigar box.

If Sidney Weinstein developed the test, why is it called the Semmes-Weinstein Monofilament test? 

Josephine Semmes was a well-known neurophysiologist working at National Institutes of Health when the monofilament thresholds were first used in landmark studies and published in the book “Somatosensory Changes After Penetrating Brain Wounds In Man” (long out of print but available through the Library of Congress). They did a lot of this work together, and according to Weinstein, he wanted to  honor Semmes by putting her name first on the test in recognition of how much he held her in esteem.

Did Sidney Weinstein only look at threshold testing with the monofilaments?

Sidney Weinstein produced many remarkable works using the nylon monofilaments in testing human subjects. Not only did he determine normal and abnormal detection threshold with the Nylon monofilaments for males and females, right and left handedness, and all over the body, he compared and found this form of testing superior to popular forms of testing such as 2 point discrimination, and point localization. His life’s work can best summed up by the title of one of his best papers “Intensive and Extensive Aspects of Tactile Sensitivity As A Function of Body part, Sex, And Laterality” (Active Touch, chapter 10). Remarkably there is no part of this chapter and his other work that is out of date today, and no investigator can boast of more extensive or careful research. The researcher into sensibility today has much to learn learn much by obtaining Weinstein's extensive original papers, and articles. He attempted to leave no stone unturned. His work has been that of life-long significant contributions; not just the Nylon monofilaments. He determined monofilament-testing superior to 2-point discrimination testing based on his studies mapping cortical areas of the brain. He found that recognition of 2-point discrimination could be extinguished by stimulating areas of the brain as an area of the hand was tested, while recognition of threshold could not. He understood this meant that our perception of 2-point discrimination is then cortically mediated, while threshold recognition is physiologic.  His argument for using threshold testing over 2-point discrimination is that the optimal and valid test needs to be physiologic.

What is Sidney Weinstein like as a man? 

A careful observer, Sidney Weinstein is a philosopher as well as a researcher. He has the “good” attributes of being obsessive compulsive. As one might expect from someone so inventive, he has a multifaceted personality and will fluently quote Shakespeare to illustrate his points. When asked if he recognized the significance of his invention of the nylon threshold test early on, he quotes the well known words of Shakespeare “In the lives of men, there is a tide…” He believes himself fortunate enough to have caught and ridden the tide in his work. He also is a talented in sculpture. His creations in wood are as artful as the man, and he could have made a life in art, as well as in science.

Those who think Sidney Weinstein looked only at monofilament threshold testing do him a disservice and not give him due credit for all of his other research. He sometimes gets too involved in his work to even think of lunch.  He is down to earth enough to enjoy a backyard feast while in Louisiana. In a world where marriage is often taken for granted, he recognizes one the best events in his life is his great fortune in marrying his wife and partner in life Margaret, joyously relating how they met. He is practical, but also a humanitarian, truly wanting to help and assist those unfortunate enough to be struck with life changing and challenging nerve problems. He is proud of his contribution of the Nylon monofilaments, and deservedly so.

Has Sidney Weinstein been recognized for his work?

Like all inventors he probably has not been recognized enough for his contributions, and his Nylon test has been copied without giving him credit. But should be acknowledged as the inventor, and we owe him that. Years ago he was given a metal by his colleagues for being one of the first of the neuropsychologists. For many years was not in direct contact with surgeons and therapists and aware of how much impact and contribution his invention of the Nylon monofilaments had made to surgeons and therapists doing peripheral nerve testing and treatment until communication was reestablished with him in the 1990’s.  He was never lost at all.  Weinstein has for decades been the editor of the International Journal of Neuroscience. In the 1990’s Weinstein was recognized for his role in developing the monofilament test at a "Biomechanics of the Hand " Seminar held at the former United States Public Health Service Hospital, in Carville, LA, and given the “Golden Monofilament Award” designed specifically for him in recognition of his contribution of the monofilament test. Following this he received the personal thanks of C. Everett Koop, the then USPHS Surgeon General. He was invited to address the Hand Rehabilitation Foundation Meeting, in Philadelphia, and to present his work at the American Society of Hand Therapists Annual Meeting. As part of his presentation he wrote a paper on “Fifty Years in the Study of Somatosensation” published in the Journal of Hand Therapy. About this time he was also knighted as Sir Sidney Weinstein by the Order of Malta for his sensory testing and other humanitarian contributions.

What has changed in the monofilament testing from the original?

Sidney Weinstein made further improvements to the original design when he rounded the tops of the Nylons, in what he has patented as the WEST (Weinstein Enhanced Sensory Test). This he certifies for calibration, and he reports it has better tip control. Sidney Weinstein continued for years to use the monofilaments and other threshold tests for the eye and dermatological applications, and again added to developments in peripheral nerve testing instrument design when he developed a treatment to round the Nylon monofilament tip for the WEST instrument. This version of the monofilament test (patented) is available today through his website and in some patient care catalogs as a Hand Set, Foot Set, and an additional set using the lightest monofilaments for Normative testing.

The original Semmes-Weinstein design is still useful and available to a large variety of clinics that need to do sensibility testing. There is nothing wrong with the original design so long as it is calibrated correctly. It has been found to sensitively and repeatedly screen and map peripheral nerve sensory changes. Nylon has the same properties today it did originally if it is pure (with no additives that can change the physical properties).

With instrumentation technology advances there is better ability to measure more precisely the dynamic force stimulus produced by each Nylon monofilament from the tiniest to the largest diameter size. Each monofilament of a specific diameter and 38 mm length produces a specific and repeatable “force of application”. Some of the Nylon sizes today when made to specifications have been found to measure slightly differently from that originally calculated and reported. Bell Krotoski's and Buford's measurement research objective was not to change the forces of application to match the calculated forces, but to identify exactly what that force of application is for each monofilament when monofilaments correctly meet their specified 38 mm length and diameter size. These measurements have been reported in studies (see references The Force versus Time Relationship of Clinically used Sensory Testing Instruments, and Repeatability of the Semmes-Weinstein Monofilaments). On Scales of Interpretation the forces are rounded in force for general understanding of changes in magnitude from a few milligrams to several hundred grams as the monofilaments increase in diameter size. The length and diameter sizes have been the consistently standard in over 30 years of clinical testing and research in using the monofilaments to screen and map peripheral nerve abnormality. If the forces of application are changed from that used in normative and other studies, years of results can no longer be used and applied to previous clinical testing. Weinstein does adjust the monofilament length slightly in his WEST to achieve his intended force of application. While he has the a physicist son with skill and measurement equipment to do this, it is not recommended that others producing the monofilaments cut off the lengths of the monofilaments due to the inherent inaccuracies found when measuring with top loading balance type measurement scales designed to measure weight and not Nylon elasticity. There is a need for specially designed equipment to measure the dynamic force produced by the visco-elastic properties of the Nylon monofilament (physical properties giving it its specific bend and recovery).

Weinstein’s original thresholds of recognition for “normal” using specified diameter and length monofilaments all over the body have been repeatedly reconfirmed in the 1950's, and with later studies using modern nylon material to consistent specifications (see references). This holds true even though Weinstein initially used an ascending and descending protocol for determining threshold, and later testing simplified the test to only used an ascending.

In 1976 definition and description was added for recognizable, repeatable, descriptive abnormal functional “levels” of sensibility worsening and recovery according to the monofilament size. This includes in particular a level for “loss of protective sensation” critical for recognizing those persons at risk of damaging their insensitive hands or feet if they do not use compensatory protective skills. Weinstein did not describe the descriptive levels of sensibility and color-coding from cool to warm according to degree of change used today. These were described in a comparison study using the monofilaments in over 200 subjects with other sensory tests published in 1978 (Bell, now Bell-Krotoski see references). Results of monofilament testing were compared in a 2 hour battery with all known sensory tests including graphesthesia, texture discrimination, 2 point discrimination, stereognosis, temperature, proprioception, pin prick, and nerve conduction velocity. It became obvious that results from the monofilaments predict relative performance on the other tests. This work can be found in the first edition of the (American) Rehabilitation of the Hand, Hunter, Schneider, Mackin, and Bell, and all subsequent editions. The Scale of Interpretation developed for the monofilaments has become standard in clinical testing. This investigation and testing was independently conducted, but before initial publication was found to have similarities with early Nylon monofilament interpretation scales developed by Kilulu von Prince, and Werner and Omer. Kilulu von Prince should be credited with first identifying and naming a “level of protective sensation” in her work finding that "protective sensation" (her terminology) was not adequately determined by presence or absence of 2 point discrimination, but by threshold detection. Many today incorrectly reference where the concept of "Protective Sensation" first developed, and like the Nylon monofilaments, it can be found credited to later investigators.

That independent examiners attempting to develop a scale of interpretation for the monofilaments found similarities in results when predicting sensibility functional recognition confirms that there exists some degree of repeatability in physical functional threshold levels of the peripheral nerves according to the level of monofilament threshold detection. Results in the earliest works were partially masked by the examiner’s changing the monofilaments thresholds recorded according to results of 2 point discrimination,  examiners requiring point localization as part of the test, and  no consistent color-coding. The 1978 study was different in that it did not change the level of monofilament threshold detected according to results from the other tests (these were separated and treated as separate tests) and mapping of peripheral nerve abnormality thus became precise and repeatable.

The color-coding scale from cool to warm colors that is now in standard use, developed in the 1978 study, was patterned after Paul W Brand FRCS’s color-coding for degrees of temperature. Consistent color-coding for level of sensory detection enabled a clear differential mapping of normal versus abnormal threshold detection and functional discrimination from a slight diminution to loss of protective sensation. This consistent color-coding greatly aided clinical and surgical treatment of patients with peripheral nerve involvement in sensitive monitoring of changes from treatment, predicting timing of return in neural function, and signaling when treatment intervention is critical to prevent permanent loss. Later first screening for areas of abnormally, and then concentrating threshold testing only on abnormal areas for degree of threshold recognition of absence shortened the test.

In the early 1980’s a mini set for the hand and body (requiring only 10 minutes) developed from the need to shorten the test and the Scale of Interpretation developed in the 1978 clinical testing. In 1984, Based on sites specific to each nerve, screen sites were determined to screen for and monitor each nerve, further shortening the test initial screen testing. The first reduced set for a Hand Screen consisted of the 5 monofilaments most often used as important for determining functional sensibility levels out of the original 20 monofilaments. (See Bell-Krotoski Hand Set, or Hand/ Body Set).

While the foot was successfully mapped in the same way as the rest of the body in the early 1980's, screen testing of feet in a Foot Set later followed by other researchers and added to the practicality and usefulness of the monofilament test.

Bell-Krotoski and others found the original monofilament instrument design repeatable within a small standard deviation if calibrated correctly. Many other handle designs have been made and even patented, but essential monofilament element in the threshold test maintained - with Nylon that bends when an intended force of application is delivered, its elastic properties absorbing some of the vibration of the examiner’s hand, producing a controlled instrument for sensory testing.

After meeting Sidney Weinstein in person and collaborating on notes and developments in clinical testing Bell-Krotoski with Sidney Weinstein, and son Curt Weinstein wrote a combined paper.  "Testing Sensibility, Including Touch-pressure, Two-point Discrimination, Point Localization, and Vibration" published in the Journal of Hand Therapy in 1993, provides shared knowledge and collective history of the monofilament testing compared with other forms of sensibility evaluation (see references). The Nylon monofilament threshold  test for determining cutaneous sensory detection remains one of the most objective tests, if not the most objective test available to clinicians evaluating and monitoring peripheral function..

The Nylon monofilament form of patient threshold detection testing is a gift to those attempting early detection of peripheral nerve abnormality, detection of protective sensation, and sensitively monitoring changes in peripheral nerve status with treatment. Despite claims that can be found in the literature by those with intent to discredit the monofilament threshold test and champion another form of testing, if compared in a fair protocol, results from the monofilament testing are unsurpassed in the sensitivity and validity, and sheer amount of information that can be derived for a person with peripheral abnormality. Even results from abbreviated testing protocols are superior and effective as commonly used in treatment of patients with various etiology peripheral nerve damage and disease, from Hansen’s disease, carpal tunnel syndrome, to diabetes.

The next time you use the Semmes-Weinstein Monofilaments, consider all has gone into their development.

J Bell Krotoski, 2008