Disease is a noumenal construct; that is, it is the basic reality behind all sensory experience in medical science. According to Kant [3], noumena are not knowable because they cannot be perceived. They must be thinkable, however, because scientific investigation cannot proceed without the assumption that they exist. One might go so far as to say that there are no diseases in everyday practice, only ill people, each of whom responds to some noxious stimulus in his or her own way. Furthermore, Engel [4] discussed folk wisdom, a repository of things medical that are not phrased in the profession's official jargon. When a disorder is neglected, its memory may be kept alive for long periods-even hundreds of years-in the popular sphere, where it can be found in historical accounts, fiction, and even newspapers.

I discuss the peregrinations of phantom limb, from its earliest known description through more than three centuries of neglect by the medical literature to its resurrection and, finally, the present day, when it is still the subject of animated debate.

History

In 1871, Silas Weir Mitchell [5] gave the first modern report of what he evocatively referred to as a postamputation sensory "ghost." Gallinek [6] compared the phenomenon to a hallucination, whereas Kolb [7] called it a disturbance of the body image. After more than a century of investigation, it remains uncertain whether phantom limb originates centrally or peripherally [8]. The experience of phantom limb is considered the rule rather than the exception after amputation and, according to Riddoch [9], is probably more common than is recognized. In phantom limb, the patient experiences a kind of cognitive dissonance, knowing that the sensation has no physical basis but perceiving it nonetheless [9]. Moreover, the amputee may fear that others may consider the phenomenon an indication of insanity or malingering [9].

The first known description of phantom limb was given by Ambroise Pare, the great 16th-century military surgeon whose many contributions to medicine are contained in a monumental 10-volume work. There is no mistaking what he had in mind when, in 1551, he wrote [10]: "For the patients, long after the amputation is made, say they still feel pain in the amputated part. Of this they complain strongly, a thing worthy of wonder and almost incredible to people who have not experienced this." The question of why Pare's description lay buried for more than 300 years and was resurrected only toward the end of the nineteenth century is a moot one.

The many historical and literary references to phantom limb indicate that the phenomenon remained in the popular mind during its period of medical eclipse. Riddoch [9], without giving a source, stated that the phantom fingers of Admiral Lord Nelson's amputated arm gave him "... a direct proof of the existence of the soul." As an amputee, Captain Ahab, the chief among the dramatis personae of Moby Dick (1851), would be expected to have first-hand knowledge of phantom limb. Indeed, the following exchange occurs between Ahab and the ship's carpenter, who is making him a new artificial limb [11]:

"Look ye, carpenter, I dare say thou callest thyself a right good workmanlike workman, eh? Well, then, will it speak thoroughly well for thy work, if, when I come to mount this leg thou makest, I shall nevertheless feel another leg in the same identical place with it; that is, carpenter, my old lost leg; the flesh and blood one, I mean. Canst thou not drive that old Adam away?" "Truly, sir, I begin to understand somewhat now. Yes, I have heard something curious on that score, sir; how that a dismasted man never entirely loses the feeling of his old spar, but it will still be pricking him at times. May I humbly ask if it really be so, sir?"

Despite the personal and popular knowledge of phantom limb evinced by Melville's interlocutors, medicine continued to ignore it for two more decades. Romberg's textbook of neurology [12], published in English translation in 1853, makes no mention of the subject.

In July 1866, an anonymously authored short story, "The Case of George Dedlow," was printed in the Atlantic Monthly [13]. It tells of a young man with medical training who is severely injured in both legs in the battle of Chickamauga during the U.S. Civil War. He has surgery and, after awakening, is unaware that his legs have been amputated. He asks an orderly to massage his left calf, where he perceives a cramp; when the orderly draws the covers back, the amputation is revealed.

In the last scene, Dedlow attends a seance. When his turn comes to conjure up a spirit, he fixes on his lost legs. Contact with them is duly established and our hero suddenly finds himself able to walk a few steps. However, as he proceeds, the legs grow shorter until he is once again walking on his stumps. The peculiar occurrence of an amputee attempting to step off on the side of the phantom limb has been described in the medical literature, as has the sense that the limb shortens over the years [5]. By the time that Mitchell published his classic paper on the sensory ghost, it had become apparent that he was also the author of "The Case of George Dedlow."

Henry Head [14], whose textbook of neurology appeared in 1920, discussed the ability of human beings to extend their sense of self outside of the body, a matter he considers relevant to phantom limb:

"It is to the existence of ..."schemata" (in the brain) that we owe the power of projecting our recognition of posture, movement and locality beyond the limits of our own bodies to the end of some instrument held in the hand. Without them we could not probe with a stick, nor use a spoon unless our eyes were fixed upon the plate. Anything which participates in the conscious movement of our bodies is added to the model of ourselves and becomes part of these schemata ... ."

Writing in 1941, Riddoch [9] seconded Head's idea of extensibility but maintained that it originated with Samuel Butler who, in Erewhon (1872), referred to tools as detachable limbs and said that the capacity to use them in this manner is one of the major characteristics that distinguishes man from the lower animals [9]. Butler's book came out a few months after Mitchell's report; in effect, Butler offered a partial explanation for a phenomenon of which he may never have heard. Finally, John Hughlings Jackson [15], an eminent British neurologist like Head, mentioned phantom limb by its present name in a paper published in 1884 and gave Mitchell full credit for its delineation.

In the past 15 years, several theories have been propounded to explain phantom limb, but none has received universal acceptance. Jensen and coworkers [16] suggest that when pain is associated with phantom limb, the mechanism is a "reminiscence" of what the limb experienced before amputation. Phantom limb could, then, be due to the establishment of a nociceptive engram in certain cerebral structures. Sherman and colleagues [17] hold that phantom limb pain is not a single syndrome but rather has many causes. For example, according to Katz [18], pain may arise through involvement of the sympathetic nervous system by activation of sensitized nociceptors in the spinal cord. Nikolajsen and associates [19] thought that the disorder had a central neuropathic component maintained by peripheral input. C-fibers that originate in the stump are constantly stimulated and, in turn, keep certain dorsal horn neurons in a state of hyperexcitability that is mediated by N-methyl-D-aspartate receptors. Nikolajsen and associates have shown that ketamine, which blocks these receptors, relieves pain in some instances.

Investigation of all of these possible subclasses of phantom limb, which derive from Mitchell's original concept of a peripheral nerve injury, requires a high degree of technologic sophistication. A further avenue of research might follow the lines of what Oliver Sacks [20] called "romantic science." Here, an attempt is made to understand the patient as a person living with his or her physical diminishment; such empathic inquiry can shed considerable light on the neurology of the self.

Crossings

The term folk wisdom seems particularly appropriate when applied to the historical and literary allusions to phantom limb. In Moby Dick [11], we have not only Ahab's testimony about an amputee's experience but also some knowledge of it on the part of the carpenter, who is not "dismasted." This suggests that the condition was widely known and that Melville mentioned phantom limb not because he was enormously erudite but because even the man on the street was aware of it.

Some hold that Mitchell published his description of phantom limb anonymously in a nonmedical magazine to test the public's reaction to a phenomenon that Pare, more than three centuries earlier, had reported as tyring the limits of human credulity [21]. When Mitchell [5] finally gave his observations a scientific shape in 1871; they differed only in degree from the fictive original.

Admiral Lord Nelson experienced phantom limb as an emanation of the soul-that is, as a positive phenomenon. Henderson and Smyth [22], who worked with hundreds of amputees at a hospital in Germany just after World War II, observed that some of them reported that the tingling sensation of phantom limb was pleasurable. Clearly, one must distinguish between the phantom limb phenomenon, which can be regarded as physiologic, and phantom limb pain, a potentially devastating condition that sometimes leads the amputee to thoughts of suicide.

Thus, after the death of Ambroise Pare, phantom limb crossed from the medical to the popular sphere. After 320 years, it came again within medicine's purview. Of course, one can never be certain that a given condition was completely forgotten for long periods, even in the present age of MEDLINE. As Strong [23] once wrote, "If you look hard enough, you will find that what you have just discovered has already been reported in the early German literature." Nevertheless, consensus establishes priority, and most authorities agree that Mitchell, who quoted Pare in his own work, was the first modern investigator to discuss the phantom limb phenomenon. Similar crossings have been described for other disorders, such as the restless legs syndrome and sleep paralysis; description of the latter is also credited to Mitchell [24].

It is difficult to understand why phantom limb was buried, medically speaking, for so long. Its resurrection is easily grasped, for it contains just that mixture of astuteness and serendipity that marks so many discoveries and rediscoveries in medicine. In this instance, Mitchell, a brilliant neurologist who was unable to serve on the battlefield for family reasons [25], was assigned to duty at a hospital for men with nerve injuries. By chance, this hospital was established in his own city during the U.S. Civil War, a cataclysm of unprecedented scope. The observation and careful note-taking that arose from this conjuncture became an important chapter in the history of medicine.

Joseph Herman, MD

Assia Community Health Centre

Netivot 80200, Israel