The Invention of Acne...

A copy of his work [source]

...was a typographical error.

The word "acne" does not come from a classical language root; that is, not in the way we usually derive our modern medical terms. It was described by a Greek physician and then mis-transcribed in a later volume of his work.

Aetius of Amida was a contemporary of Theodoric the Great (454 - 526; mentioned here in connection with Grammar). He was known for the breadth of his learning; his writings show a great knowledge of those who came before him as well as personal skill. He came out of Mesopotamia and learned medicine at Alexandria, known for its medical school.

His famous work was Sixteen Books on Medicine, in which he compiles knowledge from Galen and others of whom we would otherwise have little information: the surgeons Rufus of Ephesus and Leonidas, and the obstetricians and gynecologists Soranus of Ephesus and Philumenus. He is not completely derivative, however. He includes original treatments for eyes, ears, nose and throat, as well as goiter and rabies and others. He also addresses surgical procedures such as for a fistula or tonsilitis.

Although a Christian, he was not immune to the cures that came from non-Christian sources. He relates spells and charms popular in Egypt at the time. Also, in explaining how to help a person suffering from a bone stuck in the throat, he makes the earliest reference to St. Blaise.

As for the condition in which the skin is covered with small eruptions or peaks, he used the Greek word ἀκμή ["acme"; point]. Unfortunately, a scribal error in a later copy turned this into ἀκνή ["acne"]. The popularity of his text made this the common name for the affliction, and so it remains.

Hysteria

from a Latin copy of Gynæcology by Soranus of Ephesus

Hysteria describes two different states: exaggerated or uncontrollable emotion or excitement, and as a psychological disorder in which psychological stress can manifest physical symptoms. The word is derived from the Greek word for uterus, ὑστέρα [hystera]. Hysteria was once assumed to be solely a female medical problem.

It seems to have started with Hippocrates (c.460-c.370 BCE), who maintained that men and women had entirely different bodies: men's humors were hot and dry by nature, women's were wet and cold. Women also had different processes, such as menstruation. Hippocrates did not pass judgment on these differences; they merely needed to be addressed by the practitioner of medicine.

Aristotle (384-322 BCE), however, had other ideas. He postulated that processes like menstruation could be harmful to men, who should avoid women during that time. He also felt men's bodies were perfect and women's were flawed. Women were irrational and unbalanced—literally "unbalanced," because he believed that the uterus "wandered" in the body.

By the time medieval medicine came along, the authority of Aristotle made it clear: over-emotional women were suffering from being unbalanced because of their womb. Hysteria could be treated by removing the source of the unbalance, and the hysterectomy was "born." (Sorry.) Unfortunately, as summarized in this abstract:

The procedure was performed by Soranus of Ephesus 120 years after the birth of Christ, and the many reports of its use in the middle ages were nearly always for the extirpation of an inverted uterus and the patients rarely survived. [source]

The procedure wasn't considered remotely safe until antiseptic techniques began in the 19th century. Even so, it wasn't until the 20th century that diagnoses of hysteria declined, possibly because the general public came to understand that "hysteria" was too easily used as a label for anxiety.