The belief that new reading problems appearing later in life must be dyslexia stems from a common misunderstanding about this learning difficulty. Dyslexia is typically associated with childhood struggles, but true developmental dyslexia is a lifelong condition that does not suddenly appear in adulthood. A separate, distinct form of acquired reading difficulty, however, can manifest later in life due to specific neurological events.
Understanding Developmental Dyslexia
Developmental dyslexia is a specific learning difference that is neurobiological in origin, stemming from differences in the brain’s structure and function from birth or early development. It is characterized by persistent difficulties with accurate and fluent word recognition, spelling, and decoding abilities, despite having average intelligence. Brain imaging shows that individuals with developmental dyslexia exhibit differences in activation patterns in the left hemisphere regions associated with language processing.
This neurobiological profile suggests that developmental dyslexia is a constitutional condition, present throughout a person’s life, even if a diagnosis is not made until adulthood. While adults with this condition may have developed sophisticated coping mechanisms to mask their struggles, the underlying difficulty with phonological processing—the ability to segment and manipulate the sounds of speech—remains. Therefore, this form of dyslexia is a lifelong difference that simply may have been previously undiagnosed or compensated for.
The Difference Between Developmental and Acquired Reading Impairment
True developmental dyslexia, rooted in early neurological development, cannot be acquired in adulthood. When adults experience a sudden loss or impairment of their established reading skills, the condition is medically referred to as acquired dyslexia or, more commonly, alexia. The fundamental difference lies in the timing and cause of the difficulty.
Developmental dyslexia affects the acquisition of literacy during the initial stages of learning to read. Acquired dyslexia, or alexia, involves the loss of a skill that was previously fully established, appearing suddenly after neurological damage. This distinction is based on the etiology: one is an inherent neurodevelopmental difference, and the other is a consequence of a specific brain injury.
Causes and Manifestations of Acquired Dyslexia (Alexia)
Acquired dyslexia (alexia) results from damage to the specific brain regions that support the complex process of reading. The most frequent causes are acute neurological events, such as a stroke or a traumatic brain injury (TBI). Progressive neurological diseases, including certain forms of dementia or brain tumors, can also gradually lead to alexia over time.
The specific reading difficulty experienced depends entirely on the location and extent of the brain damage.
Types of Alexia
- Pure alexia (or alexia without agraphia) results from damage to the left occipital lobe and the splenium of the corpus callosum. The individual can write normally but has a severe inability to read, often forcing them to read letter-by-letter.
- Phonological alexia results from damage that impairs the ability to sound out unfamiliar words or non-words, suggesting a deficit in the brain’s sound-to-letter mapping system.
- Surface alexia makes reading irregularly spelled words difficult, causing the person to read by applying standard sound rules even to words like “yacht.”
- Deep alexia often involves semantic errors, where the person might read the word “dog” but say “cat,” indicating damage that disrupts the connection between the visual word form and its meaning.
Acquired reading impairment is a direct result of physical damage to the intricate neural networks governing literacy.
Diagnosis and Management for Adult Reading Difficulties
The diagnostic process for an adult experiencing sudden reading difficulty begins with a neurological evaluation, often including brain imaging like MRI or CT scans, to identify the cause and location of any structural damage. Once a neurological event like a stroke or TBI is confirmed, specialized cognitive and language testing is performed to precisely characterize the reading deficit. These assessments evaluate distinct reading components, such as the ability to process sounds (phonological awareness) and the ability to recognize whole words instantly (lexical route).
Management for acquired dyslexia typically falls under the scope of speech and language therapy, focusing on rehabilitation tailored to the specific type of alexia. For instance, someone with pure alexia may be taught compensatory strategies, such as tracing letters or using their preserved writing ability to help recognize words. Technology also plays a significant role, with tools like text-to-speech software and audiobooks helping to circumvent the reading difficulty for daily tasks. Unlike developmental dyslexia, which involves learning lifelong coping strategies, the rehabilitation for alexia aims to retrain or rebuild the damaged reading pathways, with recovery potential varying based on the injury’s severity and the intensity of therapy.