Auditory verbal agnosia : Causes and treatment
Auditory verbal agnosia (AVA), also known as pure word deafness, is the inability to comprehend speech. Individuals with this disorder lose the ability to understand language, repeat words, and write from dictation. Some patients with AVA describe hearing spoken language as meaningless noise, often as though the person speaking was doing so in a foreign language. However, spontaneous speaking, reading, and writing are preserved. The maintenance of the ability to process non-speech auditory information, including music, also remains relatively more intact than spoken language comprehension.Individuals who exhibit pure word deafness are also still able to recognize non-verbal sounds.The ability to interpret language via lip reading, hand gestures, and context clues is preserved as well. Sometimes, this agnosia is preceded by cortical deafness; however, this is not always the case. Researchers have documented that in most patients exhibiting auditory verbal agnosia, the discrimination of consonants is more difficult than that of vowels, but as with most neurological disorders, there is variation among patients.
Auditory verbal agnosia has been shown to form as a result of tumor formation, especially in the posterior third ventricle, trauma, lesions, cerebral infarction, encephalitis as a result of herpes simplex, and Landaui-Kleffner syndrome. The exact location of damage which results in pure word deafness is still under debate, but the planum temporale, posterior STG, and white matter damage to the acoustic radiations (AR) have all been implicated.
Auditory verbal agnosia is rarely diagnosed in its pure form. Auditory verbal agnosia can both present as the result of acute damage or as chronic, progressive degeneration over time. Cases have been documented that result from severe acute head trauma resulting in bilateral temporal lobe damage. In contrast, auditory verbal agnosia has also been documented to present progressively over several years. In one such case, the patient exhibited progressive word deafness over a 9-year period but did not exhibit any other cognitive of mental deterioration. MRIs showed cortical atrophy in the left superior temporal lobe region.
In childhood, auditory verbal agnosia can also be caused by Landau-Kleffner syndrome, also called acquired epileptic aphasia. It is often the first symptom of this disease. A review of 45 cases suggested a relationship between prognosis and age of onset with poorer prognosis for those with earlier onset. In extremely rare cases, auditory verbal agnosia has been known to present as a symptom of neurodegenerative disease, such as Alzheimer's disease. In such cases auditory verbal agnosia is a symptom that is typically followed by more severe neurological symptoms typical of Alzheimer's disease.
Sign language therapy
Sign language therapy has been identified as one of the top five most common treatments for auditory verbal agnosia. This type of therapy is most useful because, unlike other treatment methods, it does not rely on fixing the damaged areas of the brain. This is particularly important with AVA cases because it has been so hard to identify the causes of the agnosia in the first place, much less treat those areas directly. Sign language therapy, then, allows the person to cope and work around the disability, much in the same way it helps deaf people. In the beginning of therapy, most will work on identifying key objects and establishing an initial core vocabulary of signs. After this, the patient graduates to expand the vocabulary to intangible items or items that are not in view or present. Later, the patient learns single signs and then sentences consisting of two or more signs. In different cases, the sentences are first written down and then the patient is asked to sign them and speak them simultaneously Because different AVA patients vary in the level of speech or comprehension they have, sign language therapy learning order and techniques are very specific to the individual's needs.
In incidents where tumors and their pressure effects are the cause of pure word deafness, removal of the tumor has been shown to allow for the return of most auditory verbal comprehension.