What Is the Difference Between Aphasia and Dysarthria?

Aphasia is a broad term that refers to a partial or total loss of the ability to speak and understand language. While aphasia affects a person's ability to communicate effectively, dysarthria impacts a person's ability to speak due to damage to the parts of the brain that control the muscles of the lips, tongue, and throat, and those used for breathing.

The physiology of the brain and the science of treating brain injuries is complicated. When the language center to the brain is damaged, there are many different conditions that can result, including aphasia and dysarthria. These two conditions impact a person's ability to communicate, but there are key differences when it comes to aphasia vs. dysarthria.

Aphasia is a broad term that refers to a partial or total loss of the ability to speak and understand language. It's caused by damage to the language center of the brain, either through illness or injury. 

Stroke, which causes a lack of blood flow to part of the brain, is the most common cause of aphasia. An estimated 25% to 40% of stroke survivors will develop aphasia. 

An estimated two million people in the United States are diagnosed with aphasia, more than muscular dystrophy, Parkinson's disease, or cerebral palsy.

Aphasia symptoms can vary widely, based on the location and severity of the original brain injury. Most medical providers classify aphasia based on how the person repeats words back, if they can speak fluently, and if they can understand what is being said.

Aphasia has many subcategories and medical providers have varying opinions on which terms they prefer to use. There are three main categories of aphasia, including:

Wernicke’s aphasia. Also known as fluent or comprehensive aphasia, Wernicke's aphasia is often a result of damage to the side portion of the left hemisphere of the brain. The person will usually have trouble understanding what other people are saying but can speak in long sentences that often don’t make sense. They're often unaware that they aren't communicating effectively.

Broca’s aphasia. Also known as non-fluent or expressive aphasia, Broca's aphasia is often a result of damage to the front portion of the left hemisphere of the brain. The person usually understands what others are communicating but has difficulty choosing and saying words. They are often frustrated that they can't communicate effectively.

Global aphasia. In this more serious condition, the person has trouble understanding and expressing speech. It's usually a result of severe brain injury or disease and often comes with other conditions, such as blindness or paralysis.

No, aphasia doesn't affect your intelligence. It involves difficulty communicating ideas and thoughts through speech, not in having the ideas and thoughts themselves. However, severe brain damage — or damage to other parts of the brain besides the language center — can cause additional symptoms including cognitive problems. 

If a person has an injury or symptoms that suggest aphasia, a doctor will order tests to determine the cause, prognosis, and treatment plan. These will often include:

• Routine blood tests and X-rays
• Detailed imaging of the brain, usually with an MRI or a CT scan
• Tests for function of nerves, hearing, and vision, along with genetic tests
• Interviews with qualified doctors and speech-language pathologists to determine memory, reading, writing, speech, repetition, and other cognitive and communication skills

The prognosis, or projected outcome, of aphasia is largely dependent on the original brain injury. Many people are able to completely regain their communication skills if the original injury is minor or the person is able to fully recover. In those with more severe brain damage, recovery may take months to years, and they may never fully recover.

A good medical team and trusted speech-language pathologist will help with recovery. The treatment goals are to keep what communication skills remain, regain what skills were lost, and learn new ways to communicate — usually through pictures, gestures, or electronic communication devices. 

While aphasia affects a person's ability to communicate effectively, dysarthria impacts a person's ability to speak due to damage to the parts of the brain that control the muscles of the lips, tongue, and throat, and those used for breathing.

The symptoms of dysarthria vary widely and depend on what part of the brain was damaged. These can include:

• Difficulty moving your tongue or lips
• Speaking too quickly or too slowly
• Voice sounds weak or breathy
• Words are mumbled, choppy, or robotic

Dysarthria is caused by damage to the part of the brain responsible for the motor aspects of speech. The type of dysarthria is predicted based on the location of injury and can be categorized by the type of abnormal speech pattern:

• Flaccid dysarthria: from damage to lower motor neurons (nerves that connect the brain and spinal cord to muscles)
• Spastic dysarthria: from damage to upper motor neurons (nerves contained within the brain) of the motor cortex
• Ataxic dysarthria: from damage to the connections between cerebellum (area responsible for coordination) and other areas of the brain
• Hyperkinetic and hypokinetic dysarthria: from damage to the part of the brain that controls muscles of the head, neck, and limbs

Treatment for dysarthria largely depends on the original injury or illness. A speech language pathologist (SLP) will help assess what kind of dysarthria you have, how severe it is, and if there are any other impairments, including aphasia. The SLP may provide:

• Exercises to strengthen your speaking muscles
• Practices to say words slowly and more clearly
• Practices to strengthen your breathing muscles
• Tools to learn other ways to communicate, such as pictures, gestures, and electronic devices

Aphasia and dysarthria are both conditions that impair communication. A person with aphasia will have difficulty understanding and processing speech while a person with dysarthria will have difficulty using the muscles to speak. Both of these conditions tend to happen with similar brain injuries and illnesses, so some people can have both conditions: 

Whatever the original brain injury, and whatever resulting conditions occur, the patient’s recovery is likely to be challenging. However, there is still potential for a good quality of life — and, in some cases, full return to function.