At the age of 32 Sigmund Freud developed a new problem. Pricking and other unpleasant sensations had overtaken the skin on the outer side of his right thigh. Walking made his symptoms worse. The affected skin was exquisitely sensitive to touch and even the usual rubbing of his underclothes irritated the area.
Seven years later in 1895, when Freud wrote up his self-observations for a German medical journal, the abnormal sensations were still present, but had migrated. At first, the area of disturbance had been more noticeable near the top of the thigh, but gradually the abnormal sensations moved downward to a palm-sized area a hands breadth above the side of his knee.
When Freud squeezed a fold of skin in this area, it hurt more than it did in his left thigh. Although he could feel a pinprick as such, it also burned. Even so, individual spots within the zone of abnormal skin were insensitive to ordinarily painful maneuvers. He also noticed that temperature sense was impaired. Warm objects placed against the affected skin felt cooler than in unaffected areas. And although the original pricking sensations improved over time, his outer thigh had become generally...