At the start of the 20th century, physicians thought low back pain was caused by inflammation of or damage to the nerves, with neuralgia and neuritis frequently mentioned by them in the medical literature of the time. The popularity of such proposed causes decreased during the 20th century. In the early 20th century, American neurosurgeon Harvey Williams Cushing increased the acceptance of surgical treatments for low back pain. In the 1920s and 1930s, new theories of the cause arose, with physicians proposing a combination of nervous system and psychological disorders such as nerve weakness (neurasthenia) and female hysteria. Muscular rheumatism (now called fibromyalgia) was also cited with increasing frequency.