Why was the bone-cyst (Hadyavran) considered such an extraordinary malady in the story of the doctor's nephew?

In Chapter 34, the nephew's bone-cyst, or Hadyavran, was considered an extraordinary and most difficult malady because it was completely unresponsive to any known medical intervention of the time. The text explicitly states that no medicine could cure it and it showed no improvement whatsoever. Expert and intelligent surgeons felt exhausted and helpless after their attempts, including surgery, failed. All native and foreign treatments were tried to no avail. This complete failure of conventional and expert medical science is what marked the disease as exceptional and led the family to seek a spiritual remedy from Sai Baba.