He has a neurological illness and needs treatment.
Tips
usage
神经病 has two uses: the medical term for neurological/mental illness, and a common insult meaning 'crazy' or 'lunatic'. Context makes the meaning clear.
mistakes
Don't confuse 神经病 (shénjīngbìng, neuropathy/crazy) with 精神病 (jīngshénbìng, psychiatric illness). As an insult, 神经病 is more common and slightly less offensive.