Dyslexia is often understood as a learning difficulty that emerges in childhood, affecting how individuals process written language. However, the ability to read, which is typically acquired and stable in adulthood, can sometimes be disrupted later in life. This acquired difficulty with reading presents a different scenario than developmental forms of the condition, prompting questions about its causes and manifestations in adults.
Acquired vs. Developmental Dyslexia
Dyslexia encompasses two distinct categories: developmental and acquired. Developmental dyslexia originates in childhood, often becoming apparent when a child begins formal schooling. It is a neurodevelopmental disorder with a strong genetic component, and its underlying mechanisms stem from differences in the brain’s language processing centers from birth. This form is a lifelong condition, though its impact can be managed with appropriate interventions.
Acquired dyslexia, also known as alexia, differs fundamentally. It arises from neurological damage or disease that occurs after an individual has already learned to read. While the symptoms of acquired dyslexia might appear similar to those of developmental dyslexia, their origins are distinct. Acquired dyslexia results from specific brain injuries or conditions that disrupt the neural pathways involved in reading, affecting previously intact reading abilities.
Common Causes of Acquired Dyslexia
Acquired dyslexia typically results from a sudden neurological event or a progressive neurological condition. Stroke is a frequent cause, particularly when it affects the left hemisphere of the brain, crucial for language processing. Damage to specific areas like the angular gyrus in the left parietal lobe can lead to significant reading impairments. Traumatic brain injury (TBI) can also cause acquired dyslexia, as the physical impact can damage brain regions responsible for reading.
Neurodegenerative diseases represent another category of causes. Conditions such as Alzheimer’s disease, Parkinson’s disease, and primary progressive aphasia can gradually impair reading ability. Brain tumors, depending on their location, can also induce reading difficulties. In some instances, brain infections or complications from surgical procedures might inadvertently cause damage to critical brain tissue, leading to acquired dyslexia.
Recognizing the Signs of Acquired Dyslexia
The symptoms of acquired dyslexia involve a sudden or progressive decline in reading ability. Individuals may struggle to read words they previously knew well. Reading comprehension can be significantly impaired, even if vision remains clear. Problems often extend beyond reading to include difficulties with spelling and writing, a condition known as agraphia, which frequently co-occurs with alexia.
Some individuals might experience “pure alexia,” where they can write normally but struggle severely with reading, often resorting to a laborious letter-by-letter reading strategy. This specific type is typically linked to damage in the left occipital lobe, particularly the visual word form area. Other manifestations include difficulty recognizing letters or numbers, or a noticeable decrease in reading fluency. These reading changes are distinct from general age-related cognitive shifts, as they are typically abrupt in onset or show a clear pattern of decline.
Diagnosis and Support in Adulthood
If an adult suspects they have developed reading difficulties, seeking a professional medical evaluation is crucial. A neurologist can assess the brain’s health, while a neuropsychologist can conduct detailed cognitive assessments. Speech-language pathologists also play a significant role, specializing in the diagnosis and rehabilitation of language and reading disorders.
The diagnostic process often involves neurological examinations, comprehensive cognitive tests to evaluate reading, writing, and other language functions, and imaging studies. Techniques like Magnetic Resonance Imaging (MRI) or Computed Tomography (CT) scans can help identify the underlying brain damage or pathology responsible for the acquired dyslexia. Support strategies and interventions focus on addressing the underlying cause and rehabilitating lost skills. Speech-language therapy can help individuals re-learn reading strategies, sometimes through methods like multiple oral re-reading, where passages are read repeatedly to improve fluency and accuracy. Compensatory strategies and adaptive tools, such as text-to-speech programs, can also provide valuable support.