Cluttering (also called tachyphemia) is a communication disorder characterized by speech that is difficult for listeners to understand due to rapid speaking rate, erratic rhythm, poor syntax or grammar, and words unrelated to the sentence. One description is speech with “sudden impulsive bursts that are filled with misarticulations and disfluencies.”  The person with cluttering may experience a short attention span, poor concentration, poorly organized thinking, inability to listen, and a lack of awareness that his or her speech is unintelligible.
Stuttering is a speech disorder and cluttering is language disorder. A stutterer knows what he or she wants to say, but can’t say it; in contrast, a clutterer can say what he or she is thinking, but his or her thinking becomes disorganized during speaking.
Stutterers are usually disfluent on initial sounds, when beginning to speak, and become more fluent towards the ends of utterances. In contrast, clutterers are most clear at the start of utterances, but their speaking rate increases and intelligibility decreases towards the end of utterances.
Stuttering is characterized by struggle behavior, such as overtense speech production muscles. Cluttering, in contrast, is effortless.
Cluttering is also characterized by slurred speech, especially dropped or distorted /r/ and /l/ sounds; and monotone speech that starts loud and trails off into a murmur.
Clutterers often also have reading and writing disorders, especially sprawling, disorderly handwriting, which poorly integrate ideas and space.
A clutterer described the feeling associated with a clutter as:
It feels like 1) about twenty thoughts explode on my mind all at once, and I need to express them all, 2) that when I’m trying to make a point, that I just remembered something that I was supposed to say, so the person can understand, and I need to interrupt myself to say something that I should have said before, and 3) that I need to constantly revise the sentences that I’m working on, to get it out right. 
Another clutterer wrote on an Internet support group:
I just seem to rush through the words, and often slur words together and/or mumble—and as a result I often have to slow down, concentrate, and repeat myself.
Because clutterers have poor awareness of their disorder, they may be indifferent to speech therapy. Treatment for cluttering usually takes longer than stuttering treatment. Delayed auditory feedback is usually used to produce a more deliberate, exaggerated oral-motor response pattern. Other treatment components include improving narrative structure with story-telling picture books, turn-taking practice, pausing practice, and language therapy.
Strokes, head injuries, brain tumors, neurological diseases, or medications or drugs can stuttering. Neurogenic stuttering can result from lack of muscle control, such as Parkinson’s disease; or lack of motor planning (apraxia); or disfluencies as an aphasic individual searches for words. 
Neurogenic stuttering can have a wider array of symptoms than developmental stuttering, for example, whole word and phrase repetitions. Neurogenic stuttering typically sounds different from developmental stuttering and an experienced speech-language pathologist can immediately recognize the differences. Also, compared to developmental stutterers, neurogenic stutterers usually lack the struggle behavior and speech-related fears and anxieties. Developmental stutterers can speak certain words or phrases fluently or speak fluently in certain situation, but neurogenic stutterers generally are disfluent on everything.
Rarely, a period of stress or a traumatic experience causes a person to start stuttering. Some cases include struggle behavior, including struggle behaviors even when the person isn’t stuttering.  However, the only case of psychogenic stuttering I’ve seen had no struggle behavior, but instead was characterized by rapid-fire, effortless repetitions of initial sounds, for example, “b-b-b-b-b-b-b-b-b-b-b-baseball.” This person had the worst self-esteem I’ve ever seen, referring to herself in vulgar racial stereotypes. She was intelligent, attractive, and had a degree from a good university; yet had a low-level job and complained about the men she dated. She’d started stuttering her last semester before graduating from college. She seemed to have been given everything she needed to succeed yet was grasping for some way to fail.
This speech disorder is characterized by sudden involuntary movements of the vocal folds during speech. Some individuals have involuntary tightening of their vocal folds; others have involuntary relaxation; and still others have both. The resulting speech sounds either strained and strangled, or weak and breathy. The disorder typically affects middle-aged persons, and affects more women than men.
Hypokinetic dysarthria is the speech disorder associated with Parkinson’s disease. Please see our iParkinsons webpage.
 Guitar, Barry. Stuttering: An Integrated Approach to Its Nature and Treatment (3rd Edition) (2005, ISBN 978-0-7817-3920-7), page 445.
 Reyes-Alami, C., “Interview with a Person who Clutters,” 2004 March 3, http://www.mnsu.edu/comdis/kuster/cluttering/camil.html.
 Guitar, Barry. Stuttering: An Integrated Approach to Its Nature and Treatment (3rd Edition) (2005, ISBN 978-0-7817-3920-7), page 436.
 Guitar, Barry. Stuttering: An Integrated Approach to Its Nature and Treatment (3rd Edition) (2005, ISBN 978-0-7817-3920-7), page 444.
Very good information about cluttering. Thanks. However, I am stuck at your comment about the university girl. Maybe she has no interest in success. Maybe she can see other areas of the living experience, you say she was intelligent. Maybe it is the pressure in society to succeed, and the pressure for competition which puts her into this disorder. You’ll never know. Even psychologists and psychiatrists cannot explain everything. Experts know only what is known so far; not everything. So I think it is best to accept everybody as they are, so that everybody will feel free to evolve and heal themselves. I am sure you channeled her to a psychiatrist, maybe she was in depression, which can have a long period of precipitation. I think people go to help by an expert for a cry of help and an expert’s first job must be to channel people to other professionals, not to stigmatize.