lumbar pain vs lumbago

lumbar pain and lumbago both are nouns.

Word	Noun	Adjective	Verb	Adverb
lumbar pain	Yes	No	No	No
lumbago	Yes	No	No	No

As nouns, lumbar pain and lumbago are synonyms defined as:

lumbar pain and lumbago: backache affecting the lumbar region or lower back; can be caused by muscle strain or arthritis or vascular insufficiency or a ruptured intervertebral disc

lumbar pain (noun)	lumbago (noun)
backache affecting the lumbar region or lower back; can be caused by muscle strain or arthritis or vascular insufficiency or a ruptured intervertebral disc	backache affecting the lumbar region or lower back; can be caused by muscle strain or arthritis or vascular insufficiency or a ruptured intervertebral disc