Back trouble initially left untreated by doctor in the past (7)
I believe the answer is:
lumbago
'back trouble' is the definition.
'initially left untreated by doctor in the past' is the wordplay.
'initially' says to take the initial letters.
'by doctor' becomes 'mb' (Bachelor of Medicine, Medicinae Baccalaureus. I am not sure about the 'by' bit.**).
'in the past' becomes 'ago' ('ago' can be a synonym of 'in the past').
The first letters of 'left untreated' is 'lu'.
'lu'+'mb'+'ago'='LUMBAGO'
Can you help me to learn more?
(Other definitions for lumbago that I've seen before include "Back complaint" , "Rheumatism of lower back" , "Lower back ache" , "Rheumatic backache" , "Rheumatic pain in the small of the back" .)