aphasia vs brain disease

aphasia and brain disease both are nouns.

Word	Noun	Adjective	Verb	Adverb
aphasia	Yes	No	No	No
brain disease	Yes	No	No	No

As nouns, brain disease is a hypernym of aphasia; that is, brain disease is a word with a broader meaning than aphasia:

aphasia: inability to use or understand language (spoken or written) because of a brain lesion
brain disease: any disorder or disease of the brain

Other hypernyms of aphasia include brain disorder, encephalopathy.

aphasia (noun)	brain disease (noun)
inability to use or understand language (spoken or written) because of a brain lesion	any disorder or disease of the brain