The search for the elusive Bing sign

An extensor toe response can be elicited by a number of maneuvers, each of which has its own eponym. One of them is the Bing sign, which is intuitively appealing as we practice it by poking the dorsum of the great toe with a pin to see if the toe will extend into the pin rather than flexing away. Performing the reflex in this manner seemingly confirms that an upgoing toe is not just a sensitive patient's withdrawal response, as a voluntary withdrawal would not move towards the noxious stimulus. Given our enthusiasm for the Bing sign, we wondered what its reliability and validity would be. Interestingly, as opposed to the Babinski,^1–4 Chaddock,^1,2,4 Oppenheim,^1,2,4 and Gordon,^1,4 which have been subject to published studies of reliability and validity, the Bing does not have any published validity studies. More surprisingly, some articles do not even include the Bing sign among the list of such maneuvers, and in DeJong's The Neurologic Examination, it is listed among the minor extensor toe signs and demoted along with other techniques to the category of “clinical parlor tricks.”⁵ None of the articles that include the Bing sign provides a reference. Because the specific technique to elicit the Bing sign in recent texts is disputed^5–10 (table), and standard neurologic examination sources in the intervening period do not include such information,^11–18 we sought to clarify what Dr. Bing actually described.