The main cause of erythroderma is trauma to the sciatic nerve in the area of the pear muscle.
When the pear muscle is injured for various reasons, it can cause a local inflammatory reaction with congestion, edema and spasm, and the sciatic nerve mostly exits the pelvis from the lower edge of the pear muscle, so the aforementioned lesion of the pear muscle may compress and stimulate the sciatic nerve at the exiting pelvic area, leading to the occurrence of sciatica and causing pear muscle syndrome.