The writer picked up case about one active consequence of malnutrition? (10)
I believe the answer is:
emaciation
'consequence of malnutrition?' is the definition.
'the writer picked up case about one active' is the wordplay.
I cannot really see how this works, but
'writer' could be 'i' (the person who is writing these clues) and 'i' is found in the answer.
'about' could be 'on' and 'on' is present in the answer.
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
'active' could be 'a' (grammatical abbreviation) and 'a' is found in the answer.
This explanation may well be incorrect...
(Another definition for emaciation that I've seen is " Extreme thinness".)