Chaddock Sign
Charles Gilbert Chaddock
In 1899, the same year that Collier introduced the extensor toe sign to British readers in Brain, the 38-year-old American Charles Gilbert Chaddock introduced U.S. physicians to the Babinski sign. He later provided a full translation of Babinski's work on reflexes in the Interstate Medical Journal.
At this time, like Babinski, Chaddock was particularly interested in developing the neurological examination and identifying signs that helped to separate neurological from psychiatric illnesses (Fig. 5). Chaddock visited Babinski in Paris and returned with his own interest in delineating signs that related specifically to pyramidal tract lesions. On May 20, 1911, before the St. Louis Neurological Association, he read his paper "A Preliminary Communication Concerning a New Diagnostic Nervous Sign" (Fig. 6):
I have found the extension of one or more or all of the toes with or without fanning of them when the external inframalleolar skin is irritated in cases of organic disease is a spinal cortical reflex path. I shall call it the external malleolar sign.
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Figure 5.
Charles G. Chaddock, line drawn portrait, adapted from a photograph.
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Figure 6.
Chaddock sign. Photographs from Chaddock's original descriptions.
Chaddock was cautious to introduce a new sign and defended his observation:
In order to justify such an assumption as my title indicates it is necessary to show that what I call a new sign has not been described to my knowledge; that it is an independent manifestation, elicited in a definite way, and capable of affording diagnostic evidence of importance; that it does not occur in health or in a haphazard fashion in disease; that for practical purposes it does not require a technique too complicated for routine application; and that its manifestation is clear enough for reliable interpretation.
He carefully delineated his method, emphasizing proper relaxation of the leg, clear visibility of the foot and toes for easy detection of the sign, and the use of a dull steel point (a nail file, preferably). In his publications, he took advantage of the evolving field of medical photography and demonstrated testing techniques and different nuances of his sign. The entities in which he found the sign included skull fractures and unilateral and bilateral brain lesions, as well as spinal cord disorders. He did not find it in neuropathies or tabes dorsalis.
Chaddock found that his reflex had some advantages over the Babinski sign and that the two in combination could be particularly useful. He found that the scraping of the bottom of the foot was often confounded by withdrawal reactions that compromised confident interpretation. Withdrawal reactions were much less frequent with his reflex. In addition, he found that his sign often, in fact usually, occurred bilaterally even with a unilateral Babinski sign. To his interpretation, the sign therefore unveiled objective evidence of pyramidal dysfunction without the lateralized specificity of the Babinski sign. He suggested that crossed and uncrossed fibers occurred to innervate the lateral portion of the foot. Furthermore, his sign could appear before a Babinski sign developed and linger after a Babinski sign resolved as late evidence of a prior lesion. In some cases, it appeared even when a Babinski sign never occurred. He also described a comparable sign in the upper extremity. To stretching stimuli on the ulnar side of the palmaris longus and the flexor carpi radialis, the normal contraction of the hypothenar muscles gave way to wrist flexion with finger spreading in cases of pyramidal tract disease. In the spirit of an early rating scale, Chaddock used "slight," "marked," and "very marked" to describe his signs, though the anchoring description for each rating was not specifically delineated.
Chaddock, the Man
Chaddock was born in 1861 in Jonesville, Michigan. He completed his medical education in 1885, the same year that Babinski joined Charcot at the Salpêtrière. At this time, Chaddock took a post at the little known North Michigan Asylum in Traverse City. As a reflection of his work environment, his early writings concerned psychiatric topics. In the tradition of most aspiring American neurologists of the late 19th century, Chaddock spent a year studying in Europe (1888 to 1889). In 1892, he became Professor of Neurology and Psychiatry at the Marion-Sims College, which later became the Medical Department of St. Louis University. With this post, his writing shifted to more neurological topics, and he became increasingly interested in differentiating psychiatric from neurological clinical syndromes. His St. Louis neurological colleagues included C.H. Hughes, founder of the journal Alienst and Neurologist; Malcolm Bliss; Frank Fry; and Sidney Schwab. He traveled in Europe again from 1897 to 1899 and spent most of this time in Paris as an assistant to Babinski. Later, he frequently returned to Europe for long summer stays in France. Besides Babinski, his other main European colleague was Ramón y Cajal. Chaddock was a tall man of aristocratic bearing, well read and interested in poetry and history. His well-known Epicurean tastes may have been cultivated by his close contacts with Henri Babinski.
Context and Significance
Chaddock was highly invested in Babinski's review of his work and sent descriptions of his studies to Paris. Babinski's brother, Henri, replied that his brother found the reflex of particular interest:
My brother asked me to let you know that he has verified your observation on the reflexes. He finds your works very interesting and would be delighted to discuss them when you visit Paris again.
The letter also contains a request by Henri Babinski for Chaddock to help in marketing his cookbook in America. Whereas this letter suggests that Babinski favored the reflex, there is no mention of Chaddock's reflex in Babinski's later works.
Although attributed to Chaddock, the external maleolus sign was discovered before him and reported by the Japanese physician Yoshimura (1879 to 1945):
The extension of the big toe may be obtained by stimulating the dorsal lateral aspect of the foot from the posterior portion of the skin beneath the external malleolis anteriorly along the external edge of the foot. . . . In examining for Babinski's phenomenon, the stimulation of the dorsum should never be forgotten even if the stimulation of the sole provokes the flexion of the big toe.
The Chaddock sign is described in many standard textbooks of neurology, but it never displaced the Babinski response for the detection of pyramidal tract lesions. Nonetheless, Chaddock's original observations of his sign's presence in pyramidal tract lesions even when the Babinski sign could not be elicited remains confirmed. In modern times, Tashiro examined 13 patients and found that the Babinski response was present in 79%, whereas a positive Chaddock sign occurred in all. Early neurologists did not wrestle with the statistical issues of sensitivity and specificity but were clearly conscious of the complementary nature of different neurological signs that composed the thorough neurological examination. Some investigators have suggested that lesions involving the motor cortex (Brodmann Area 4) and its descending pathways are followed by both a Babinski toe extensor and Chaddock signs, whereas lesions of the premotor cortex (Brodmann Area 6) and its descending fibers provoke the Babinski fanning response without a Chaddock sign, but instead a Hoffman sign and forced grasping reflexes. These distinctions, however, are not consistent enough to be reliable indicators of anatomical localization; therefore, both Babinski and Chaddock signs should be considered as complementary indices of pyramidal tract impairment.