Definition of aphasia and its most important types

1. Big picture

Aphasia is one of the most important cortical signs in neurology because it immediately tells you that the lesion involves the dominant hemisphere language network, usually the left hemisphere. In the exam, aphasia is not just “speech difficulty.” It is a disturbance of language processing: speaking, understanding, naming, repeating, reading, or writing.

The key exam idea is:

Aphasia = dominant hemisphere language disturbance. It is different from dysarthria, dysphonia, confusion, dementia, or peripheral cranial nerve weakness.

A patient with aphasia may have normal tongue movement, normal voice, and normal consciousness, but cannot use or understand language properly because the cortical language system or its connections are damaged.