Difficulty with speech can be the result of problems with the brain or nerves that control the facial muscles, larynx, and vocal cords necessary for speech. Likewise, muscular diseases and conditions that affect the jaws, teeth, and mouth can impair speech. Some conditions that affect speech are present at birth (such as inborn muscular conditions and congenital anatomical abnormalities), while others are the result of metabolic diseases, infections, tumors, or injury. Abnormalities of the vocal cords such as inflammation, polyps, cysts, and tumors can affect the pitch and quality of the voice.

A number of different types of speech impediments can occur, and many terms have been used to qualify speech disorders. Aphasia is the loss of the ability to understand language, whether spoken or written, and occurs due to disturbances in the areas of the brain that are used in language processing. Dysarthria refers to a difficulty in pronouncing certain sounds or words that is usually due to a problem with muscle control. People with dysarthria exhibit slurred speech and may have problems with swallowing. Spasmodic dysphonia is a condition characterized by difficulty speaking because of repetitive or continuous spasms (dystonia) of the muscles that control the vocal cords. Apraxia of speech, also known as verbal apraxia or dyspraxia, is a speech disorder in which a person has trouble saying what he or she wants to say correctly and consistently.

Because of the numerous types of speech difficulty that can arise from various disease processes, the list of conditions that can cause difficulty with speech is very broad.

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