Horner's Syndrome:
A Medical Discovery from the American Civil War

Gary E Cordingley, MD, PhD
William Keen, M.D., diagnosed and described a case of "Horner's syndrome"
-- a cause of unequal pupils -- in an injured Civil War soldier five years before
Johann Friedrich Horner rediscovered the condition that has been known by
his name ever since.
Unequally sized pupils in combination with a drooping eyelid on the side of the smaller pupil and decreased
sweating on the same side of the face is known as Horner's syndrome, named for Johann Friedrich Horner, a
Swiss ophthalmologist who wrote up a case in 1869. When present, Horner's syndrome indicates interruption of
the sympathetic nervous system on that side of the body and is still a valuable tool in modern diagnosis.

The sympathetic nervous system helps govern various functions outside conscious control, like pulse, blood
pressure, sweating, etc. The portion of the sympathetic pathway influencing the eyes and face follows a
convoluted pathway that starts in the brain and flows down through the brainstem to the spinal cord. At the base
of the neck, the pathway passes outward from the spinal cord and through the top of the lung. From there it rises
through the neck again and into the head where it finally reaches the eye and face. A pair of otherwise identical
sympathetic pathways serves each side of the head.

While Horner's observations were valid and the syndrome has been known by his name ever since, he was not
the first to recognize this condition. Instead, an American physician by the name of William Keen first diagnosed a
case of "Horner's syndrome" in an injured Union soldier during the American Civil War. The soldier, Edward
Mooney, had been shot through the right side of his neck at the battle of Chancellorsville.

In 1864, along with fellow physicians, Silas Weir Mitchell and George Morehouse, Keen published a small book,
"Gunshot Wounds and Other Injuries of the Nerves," that included Mooney's case report under the title "Wound of
the Sympathetic Nerve." Fresh out of medical school when he entered military service, Keen made the diagnosis
upon recognizing the similarities between the soldier's face and that of a cat illustrated in a textbook of physiology.

In 1905, near the end of Keen's career as a pioneering neurosurgeon, the College of Physicians of Philadelphia
published his reminiscences about the case:

"The first nervous case that I remember was a very remarkable one, and the first of its kind ever recorded. It
occurred while I was executive officer at the Satterlee Hospital, West Philadelphia. As executive officer it was my
duty to assign new patients to the wards, and also to transfer the cases in the specialties, such as the eye,
nervous diseases, and injuries, etc., to the special hospitals. One morning, as I sat at my desk, a soldier applied
for assignment. On looking up at him I said to myself: 'You are Dalton's cat.'

"Those familiar with Dalton's good old textbook of physiology will remember a cat whose right cervical sympathetic
nerve [the portion in the neck] had been severed. The left pupil is very large, the right one very small, and the
moment I looked at this man I was struck by the similar condition of his pupils. I quickly asked him, 'Where are you
wounded?' and when he pointed to his neck I said to myself again, 'That ball destroyed the sympathetic nerve.'

"In the autumn of 1864 I took a copy of [our] book to Claude Bernard, in Paris, [a legendary physiologist and] the
discoverer of the function of the cervical sympathetic and the effect of its division [cutting] upon the pupil and the
blood vessels. He exhibited true Gallic enthusiasm when I showed him the first recorded case in the human
subject, which confirmed his brilliant researches."

"Dalton's cat" was a drawing in John Call Dalton's "A Treatise on Human Physiology." Keen attended Jefferson
Medical College in Philadelphia between 1860 and 1862, and may have seen the drawing in either the first edition
(1859) or second edition (1862). At a time when medicine was struggling to gain a scientific footing, Dalton's
writings were notable for being based on experimental observations. Dalton was one of America's first
physiologists and had studied with Claude Bernard after graduating from Harvard Medical School in 1847.

(C) 2006 by Gary Cordingley