What Causes Severe Pain In The Toe?

Four years ago my husband got a severe pain on the top of his right big toe where the toe contacts the foot. We have been to several specialists to seek a diagnosis and treatment however, it has stumped them all. They have x-rayed and found no spur, arthritus, abnormality or anything and sent him home with $400 foot cream to apply twice a day for pain. Even the foot cream doesn't work to control the pain. Can you help us?