The most common and most likely answer to this crossword clue is the 8 letter word AGRAPHIA
A
G
R
A
P
H
I
A
More clues leading to the result AGRAPHIA
Buddy explains!

The straight part
We know that "Problem for patient with brain lesion" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case problem for patient with brain lesion = agraphia.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does AGRAPHIA mean?
AGRAPHIA noun- A loss of the ability to write (usually resulting from a brain injury).
- The inability to write.