Doctor issued cause of atrophy (6)
I believe the answer is:
disuse
'cause of atrophy' is the definition.
(I've seen this in another clue)
'doctor issued' is the wordplay.
'doctor' indicates an anagram.
'issued' anagrammed gives 'DISUSE'.
(Other definitions for disuse that I've seen before include "Neglect; abandonment" , "Issued (anag)" , "Neglect; desuetude" , "Fall into this state to be unemplyed? (6)." , "State of not being employed" .)