Monday, June 8, 2015

The Babinski confession

On December 5, 2012, I had written:

I cannot remember when I last incorporated Babinski testing as a component of my standard neurological examination. When a Babinski sign is present in isolation, its significance is often obscure; when a Babinski sign is present together with hyperreflexia, hypertonicity, etc., it generally is superfluous. I do keep it in my back pocket for those times when the more informative findings of hyperreflexia, hypertonicity, etc., are ambiguous.

I also may pull it out of my back pocket when there is suspicion of Friedreich's ataxia. In any event, it has remained firmly in my back pocket for many years.

Not unexpectedly, this elicited a rather brusque response from my mentor, hereafter Dr. Mentor, of many years ago:
Its very troublesome to hear that some are not testing the plantar response as it is one of the more reliable signs in clinical neurology. Perhaps we do not rely on our skills as much with the over use of imaging and other techniques but like any other single component and more than most components the Plantar response is a useful part of the neurological examination and we "skip" it at our peril.
Another distinguished pediatric neurologist replied:
I can't recall an instance in which I have ever disagreed with an observation made by Dr. Mentor and have never been in more agreement than with his observations concerning the Babinski sign ("...the most important in clinical neurology"). I would add that this elegant part of the examination must be done properly, particularly in the neonate.
My reply:
I would like to acknowledge Dr. Mentor as someone instrumental in fostering my interest in and knowledge of pediatric neurology when I was a medical student and he was junior faculty. This, of course, does not mean that Dr. Mentor is in any way responsible for the deviancies of his acolyte. No matter how eloquently the Babinski sign is elicited, how much neurological showmanship goes into its demonstration, my question is its utility in the assessment and management of patients. As regards showmanship, I remember during my adult neurology training the chief resident repeatedly stroking a foot until on the tenth attempt or so, the toe extended. The chief resident looked at us significantly and said, "Any upgoing toe is significant!" I will do penance in this regard, if and when I can be convinced that my modus operandi has in any way impaired my diagnostic acumen, impeded the care and management of my patients or imperiled any patient. Certainly, I do not believe that I have ever generated a serendipitous Babinski sign and then told a parent with serious mien that there is evidence of brain damage in their child.


  1. Others who rushed in where angels feared to tread:

    Miller TM, Johnston SC. Should the Babinski sign be part of the routine
    neurologic examination? Neurology. 2005 Oct 25;65(8):1165-8.
    The Babinski sign is a well-known sign of upper motor neuron dysfunction that is widely considered an essential element of a complete neurologic examination. Little is known about reliability and validity of this sign. A less well-known sign of upper motor neuron dysfunction, decreased speed of foot tapping, also has not been carefully evaluated. Scientific evaluation of findings of the physical examination is crucial in directing busy clinicians.
    Ten physicians (five neurologists and five non-specialists) examined each foot of 10 subjects, 8 of whom had known unilateral upper motor neuron weakness, 1 had bilateral leg weakness secondary to ALS, and 1 had no known neurologic deficits. Our main outcome measures were inter-rater reliability (kappa values) and accuracy (agreement with known upper motor neuron weakness).
    The reliability of the Babinski sign was fair (kappa 0.30) and was substantial for foot tapping (kappa 0.73). Agreement with known weakness was 56% for Babinski sign and 85% for foot tapping. Reliability and accuracy for both tests were similar for neurologists and non-specialists.
    The interobserver reliability and validity of the Babinski sign for identifying upper motor neuron weakness are limited. Slowness of foot tapping may be a more useful sign.

    The response:

    Landau WM. Plantar reflex amusement: misuse, ruse, disuse, and abuse.
    Neurology. 2005 Oct 25;65(8):1150-1.

    Every century-old truism of clinical neurology is worthy of critical review. But not every critical review is worthy. Miller and Johnston’s 1 kappa statistical demise of the Babinski sign invites the prescription of C.R.A.P. (Circular Reasoning or Anti-intellectual Pomposity) detectors.2 In regard to upper motor neuron impairment (UMNI), they test the competitive reliability in the neurologic examination between elicitation of a hyperactive spinal reflex and impaired performance of a voluntary motor task. Validation is by correlation with the gold standard deficient performance of another voluntary task. The three phenomena are 1) extensor plantar reflex (Babinski sign), 2) slowed foot tapping, and 3) leg weakness.

  2. Miller and Johnston's response to their critics:

    Relying on aphorisms from legendary neurologists or on expectations based on pathophysiologic arguments is unscientific. In the end, any test should withstand rigorous empirical testing...

    We agree with Dr. Brenner that the Babinski sign should remain an important tool for expert neurologists, especially in patients who are unable to participate in the examination, where the sign may serve as a “red flag.” However, our study suggests that busy clinicians (especially non-neurologists) might do better to focus on other aspects of the neurologic examination, such as speed of foot tapping.

    In clinical practice, how often is the plantar response retested until it agrees with the expectation in a particular patient? Why is the sign so difficult to teach our residents and students? Why do we tolerate equivocal responses and create complex rules to differentiate withdrawal from a true Babinski sign? Bias is everywhere.

    See: Khatri BO. Should the Babinski sign be part of the routine neurologic
    examination? Neurology. 2006 May 23;66(10):1607-9; author reply 1607-9.

  3. In spite of its hallowed status, is there validity to criticism that the Babinski sign may lack diagnostic accuracy? In the cohort study by Jaramillo et al. presented in this issue, a broad spectrum of patients with suspected pyramidal tract dysfunction was evaluated employing a sensible composite independent reference standard. Incorporation bias was avoided by excluding consideration of the Babinski sign in the reference standard. Investigators performed and interpreted both the index test and the reference standards in a masked fashion. Not surprisingly, the Babinski sign was confirmed to have a very high specificity for pyramidal tract dysfunction. When present, it was a highly accurate “rule-in” finding, justifying its value in the clinical examination. By contrast, its sensitivity was modest indicating that its absence did not rule out PTD and where suspected, further assessment is indicated. The confidence traditionally placed by clinicians on this simple test is justified; albeit, with the preceding caveat.

    Sumner AJ. The Babinski sign. J Neurol Sci. 2014 Aug 15;343(1-2)

    Isaza Jaramillo SP, Uribe Uribe CS, García Jimenez FA, Cornejo-Ochoa W,
    Alvarez Restrepo JF, Román GC. Accuracy of the Babinski sign in the
    identification of pyramidal tract dysfunction. J Neurol Sci. 2014 Aug


    The extensor plantar response described by Joseph Babinski (1896) indicates pyramidal tract dysfunction (PTD) but has significant inter-observer variability and inconsistent accuracy. The goal of this study was to determine the accuracy of the Babinski sign in subjects with verified PTD.
    We studied 107 adult hospitalized and outpatient subjects evaluated by neurology. The reference standard was the blinded and independent diagnosis of an expert neurologist based on anamnesis, physical examination, imaging and complementary tests. Two neurologists elicited the Babinski sign in each patient independently, blindly and in a standardized manner to measure inter-observer variability; each examination was filmed to quantify intra-observer variability.
    Compared with the reference standard, the Babinski sign had low sensitivity (50.8%, 95%CI 41.5-60.1) but high specificity (99%, 95%CI 97.7-100) in identifying PTD with a positive likelihood ratio of 51.8 (95%CI 16.6-161.2) and a calculated inter-observer variability of 0.73 (95%CI 0.598-0.858). The intraevaluator reliability was 0.571 (95%CI 0.270-0.873) and 0.467 (95%, CI 0.019-0.914) respectively, for each examiner.
    The presence of the Babinski sign obtained by a neurologist provides valid and reliable evidence of PTD; due to its low sensitivity, absence of the Babinski sign still requires additional patient evaluation if PTD is suspected.

  4. From an eminence grise:

    I would add that this elegant part of the examination must be done properly, particularly in the neonate. The neonatal foot is especially sensitive to stimuli that are nociceptive or involve the tickle phenomenon and a positive response may be inhibited when the foot is cold or the knee is excessively flexed. The errors in interpretation are reliably alleviated if the observations of Babinski (in every way one of the truly remarkable figures in neurology, a gentlemanly and clear thinker who was able to set several of the subjects on which Charcot chose the route of showmanship over clinical science science) are remembered. Other than his refinements of positioning necessary to elicit "his" reflex It is of greater importance still to recall that the abnormal form of the "phenomene des orteils" (great toe dorsiflexion) entails the signe de l'eventail." (fanning of the four lateral toes with comparatively little dorsiflexion. Neonatal dorsiflexion/withdrawal of all toes is not an abnormal sign while upgoing great toe with the signe l'eventail is (not only in my opinion) nearly always abnormal in the full-term neonate—especially if the examiner's non-stroking had is placed under the thigh where it may appreciate the associatedly abnormal Brissaud reflex. The reflex is enhanced by head turning in either direction from the midline.

    Confusion on this point—the importance, examination method, and nature of the Babinski sign--has generated the many incorrect observations in print that the positive Babinski sign is acceptable in the full-term neonate. These persistently incorrect assertions can only be made by individuals ignorant of the fine four-decade+ old papers by Gwen Hogan and by Joe Volpe on this subject. Finding a true Babinski sign in the full-term neonate is a very valuable demonstration of pyramidal injury. Nice to mention Gwen Hogan (UVA nursing grad 1948, fifth woman to graduate from UVA med (1955)/4th graduate of our neurology residency neurology residency in 1961 (both undertaken by this very determined nurse because Drs. "didn't know anything about the nervous systems of neonates"). The conjunction of these two names underline Gwen Hogan's greatest contribution to neurology—she interested the future greatest neonatal neurologist, medical student/developmental neurochemist Joe Volpe, in undertaking the study of the newborn. Given the space limit we can't now consider the Mayor, Riddoch, Oppenheim, and so many other pyramidal signs or effects of head positional on other reflexes or for that matter such additional contributions of Dr. Hogan, such as the regional entity she termed "familial biscuit poisoning." I'd welcome any list folks sending me other observations on Gwen Hogan—I am fixing to put her up yet again for the "Outstanding woman graduate in medicine" award of UVA. (continued)

  5. From an eminence grise (continued):

    It is indeed the case that a positive Babinski sign may be found in Friedreich ataxia, but fixed and non-fixed toe dorsiflexion in that condition render determination of the difference between false and positive responses equivocal. That however is a condition in which there are many other important signs, perhaps the most important of which early in the course of illness is the partial loss of vibratory apprehension (pallanaesthesia). This is a test that is sometimes done poorly and often overlooked. To assess the early partial loss a 128 C tuning fork must be struck particularly hard (rendering about 21 seconds of appreciable vibration) with the examiner determining normal persistence of apprehension by placing her/his finger on the other side of the distal joint of the great toe. Early in Friedreich the usual partial pallanaesthesia is 5-7 seconds, with young men tending *possibly* to have a greater degree of loss than young women. Of course, the diagnosis is suspected because of the hammer toe changes and the quite characteristic peculiarity of gait involving the quite characteristic dyscoordination during walking of the with the three vertical body segments (legs/trunk/head)--I think that Wilson pointed this out but will have to check. A recent post concerning what to do with Wilson's two-volume text should have generated the response "hang on to it at all costs--it is one of the greatest treasures in neurology.

  6. A Fishmanism: I really wish Babinski had gone into architecture.