The irreversible forms are caused by several diseases, most commonly Alzheimer's, Parkinson's, and repeated strokes. Some treatable causes include depression, drug toxicity and thyroid dysfunction. Language deficits are present in all dementia patients and are proportional to their mental function. These deficits are subtle at first and slowly progress. In the early stages articulation, syntax, and fluency are intact, but descriptions are elaborate with little informational content.
Anomia is present and comprehension is affected by attention and memory deficits.
As dementia progresses anomia and substitutions are more pronounced and patients have difficulty maintaining a topic, saying meaningless and unrelated phrases. Comprehension and memory become significantly impaired along with disorientation to time and place. Some useful tactics are getting eye-contact to make sure you have their attention, avoiding the use of pronouns, being redundant and only talking about one topic at a time, announcing topic changes, using illustrations or visual aids, using orientation and memory aids, and demonstrating instructions. All components of speech can be affected, while comprehension can be normal. Dysarthritic speech can vary depending on the site of the lesion.