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The first step when you see a medical professional will be to receive a detailed clinical exam. Your doctor will assess your ability to read and to understand language, as well as your ability to speak and to effectively articulate your thoughts.  In addition to examining your language and communication abilities, your doctor will do a full mental and neurological exam to assess for any other cognitive or brain-related abnormalities. Your doctor will ask you questions about how you are functioning in day-to-day life, and areas of your life that have been impacted by your condition. The reason that your doctor will ask so many questions and perform such a detailed exam is mainly to rule out the possibility of other conditions. If other areas of your life are affected, and if you show other signs of mental deterioration, you may have another condition such as Alzheimer's disease which has more widespread manifestations than simply affecting language and communication.  Alzheimer's disease is the main disease that is confused diagnostically with progressive aphasia.  The main difference between the two is that Alzheimer's disease is a widespread form of dementia that will negatively impact many areas of your life, such as memory, language and communication, knowing appropriate social behaviour, and being able to perform tasks required for day-to-day life. Progressive aphasia, on the other hand, presents as a decline only in language and communication abilities (it is only this area of the brain that is damaged, which differs from a more widespread form of dementia). Therefore, declines in function will ALL be related to language and communication issues, with little to no memory problems or other concerns. As part of the diagnostic process, you will most likely receive either a head CT scan or an MRI. This is because, in addition to ruling out other mental conditions, your doctor will want to rule out potential signs of a stroke or traumatic brain injury. This is best done with the combination of a neurological exam and imaging techniques (either CT or MRI).  If your CT or MRI is consistent with the possibility of progressive aphasia, and your clinical exam supports this as well (i.e. your clinical exam shows mental deterioration associated with language and communication only, and affecting no other areas of your life), your doctor will assign you a diagnosis of progressive aphasia. It is key to understand that progressive aphasia cannot officially be diagnosed (i.e. proven) until the time of autopsy (that is, following death when doctors look at your brain and evaluate the specific areas of brain damage).  Similarly, other forms of dementia such as Alzheimer's Disease also cannot be officially diagnosed until after death, at the time of autopsy. They are all "clinical diagnoses," meaning that your doctor will evaluate the imaging results (from CT or MRI) combined with your clinical signs and symptoms and assign you the best possible diagnosis that accounts for everything, as far as he or she can tell. This is also why regular follow-up exams are important, to see if any of your signs or symptoms change. For instance, if you initially presented to your doctor with only language and communication deficits, and subsequently begin experiencing significant memory loss and other cognitive problems, your diagnosis may be changed in light of the new symptoms you are experiencing.
Receive a detailed clinical exam. Rule out other conditions that may present similarly. Have a head CT or MRI.