Can dyslexia be caused by an illness or a brain injury?
The information on this website is focused on developmental dyslexia — the type of dyslexia that is genetically influences and becomes apparent in early childhood.
When dyslexia develops later in life tied to brain illness or injury, it is called “acquired dyslexia” — the symptoms may very well be the same, but the underlying cause is different. Developmental (childhood) dyslexia is tied very closely to the process of brain development — the symptoms or the skills that are impaired do not develop in typical ways. The brain has developed normally, but in a way that makes it more difficult for the child to acquire skills such as learning to read in the same way as most other children.
In acquired dyslexia, the person’s brain had developed the ability to function in a typical way, but some sort of event, such as an illness or head injury, has caused damage to the brain that impairs that function. The exact type of impairment and prognosis for recovery is variable because there is an essentially unlimited number of ways and levels of severity that brains can be damaged.
It is of course possible for a person to have both. For example, a person with a childhood history of dyslexia might experience an illness or injury that makes things worse. This situation is fairly common with head injuries such as a concussion.