Speech and Language Disorders
Mayo Clinic speech–language pathologists are involved in clinical research aimed at answering questions about a variety of congenital, developmental, and acquired disorders that affect speech and language abilities. Their goal is to improve clinical understanding, diagnosis, prognosis and management of speech disorders. With their broad expertise spanning speech and language pathology; linguistics; phonetics and psychology; and speech–language disorders, Mayo Clinic speech pathologists use a multidisciplinary approach to conduct their research.
The Division of Speech Pathology has a long history of significant contributions to the description, diagnosis, and understanding of neurologic communication disorders, particularly motor speech disorders (e.g., the dysarthrias and apraxia of speech).
In the late 1960s, several seminal publications by speech–language pathologists Fredrick L. Darley, Arnold E. Aronson and neurologist Joe R. Brown described the distinctive speech characteristics associated with dysarthria, resulting from neurologic diseases affecting various components of the motor system. This work established a system for classifying the dysarthrias now used throughout the world.
Drs. Darley, Aronson, and Brown, in collaboration with numerous speech pathology fellows and other Mayo neurologists, subsequently published numerous papers that contributed importantly to our understanding of apraxia of speech and the speech characteristics associated with dysarthrias associated with a variety of neurologic diseases (e.g., stroke, multiple sclerosis, motor neuron disease, Wilson’s disease, Shy–Drager syndrome, Parkinson’s disease).
In recent years, Drs. Joseph R. Duffy and Edythe Strand (speech pathologists), in collaboration with speech pathology fellows and neurology consultants, have published numerous additional papers addressing the speech deficits associated with a variety of other disorders (e.g., progressive supranuclear palsy, corticobasal degeneration, paraneoplastic cerebellar degeneration, primary progressive aphasia, progressive apraxia of speech, and childhood apraxia of speech). This work, conducted over many decades, continues and has had a strong influence on the classification and understanding of neurologic motor speech disorders.
Today, the system used for classifying the dysarthrias in many parts of the world, is often referred to as the "Mayo classification system."
Major areas of research
Mayo Clinic speech–language pathology researchers are active in studying:
Joseph R. Duffy, Ph.D., researches motor speech disorders (the dysarthrias and apraxia of speech), acquired aphasia, and acquired psychogenic speech disturbances. The primary focus of his research is on defining distinguishing clinical characteristics, establishing neurologic correlates, and refining differential diagnosis.
Edythe A. Strand, Ph.D., engages in research in neurologic speech and language disorders in children and adults. Her primary interests concern the language and speech changes associated with degenerative disease and the acquisition of speech in children with motor speech disorders. She has examined the relationship of perceptual to acoustic; and physiologic measures of speech and voice in patients with amyotrophic lateral sclerosis. Her goal is to better understand disease progression and facilitate clinical intervention with progressive dysarthria in degenerative disease. As part of the clinical ALS team at Mayo, Dr. Strand studies changes in speech as they relate to changes in respiratory status and swallowing in order to enhance the ability of the clinician to predict the rate of progression of this disorder in order to determine when interventions for may be necessary.
Recent research advances
Dr. Duffy retrospectively reviewed 80 patients with apraxia of speech (AOS) as a predominant or only sign/symptom of a neurodegenerative disease. (Aphasiology, 2006 20 (6), 511–527.) The study established that patients whose communication difficulties reflected a predominant AOS tended to eventually receive clinical neurologic diagnoses characterized by predominant motor as opposed to cognitive deficits (e.g., corticobasal degeneration, progressive supranuclear palsy, motor neuron disease). In a follow–up study in which Dr. Strand also participated, the history, presenting complaints, neurological findings, and speech–language findings of seven patients with motor neuron disease (MND) and AOS were described. The findings establish that AOS can occur in MND, typically also with dysarthria, but not invariably with aphasia or other cognitive deficits. Thus, a diagnosis of MND does not preclude the presence of AOS. More important, MND should be a diagnostic consideration when AOS is a prominent sign of degenerative disease. (American Journal of Speech Language Pathology, 2007 Aug;16 (3):198–208.)
Dr. Duffy and Dr. Strand have worked with other Mayo colleagues to determine whether clinical subtype of aphasia and AOS are associated with certain pathological diagnoses and specific biochemical and anatomical structural abnormalities. Voxel–based morphometry revealed the premotor and supplemental motor cortices to be the main cortical regions associated with AOS, while the anterior peri–sylvian region was associated with non–fluent aphasia. The results suggest that refining the classification of the degenerative aphasias and AOS may improve our understanding of the relationships among behavioral, pathological, and imaging correlations (Brain, 2006 Jun;129(Pt 6):1385–98. Epub 2006 Apr 13.)
In another study, Dr. Duffy worked with Mayo colleagues to investigate the pathology causing primary progressive aphasia (PPA). They compared clinicopathologic and MRI features of subjects with PPA and AD pathology to subjects with aphasia and frontotemporal dementia with ubiquitin inclusions (FTLD–U) pathology and subjects with typical AD. They concluded that a temporoparietal pattern of atrophy on MRI in patients with progressive fluent aphasia and relatively preserved processing speed is suggestive of underlying Alzheimer disease pathology rather than frontotemporal lobar degeneration with ubiquitin–only immunoreactive changes. (Neurology, 2008 Jan 1;70(1):25–34.)
Dr. Strand is engaged in the development of a treatment program for childhood apraxia of speech, a speech disorder due to deficits in planning and programming speech movement gestures. The treatment is designed to facilitate acquisition of speech motor control in younger children or children with severe apraxia of speech. She is studying the efficacy of the treatment, known as Dynamic Temporal and Tactile Cueing for Speech Motor Skill (DTTC). Studies to date have shown a positive effect for most children treated with this method. (Journal of Medical Speech Pathology, 2006, 14: 297–307; Journal of Medical Speech Pathology, 2000, 14: 297–307; Journal of Medical Speech–Language Pathology, 2008, 16: 180–190.)
Dr. Strand is developing a speech examination that improves the differential diagnoses of speech sound disorders in young children. This examination procedure is known as the Dynamic Assessment of Motor Speech Skill (DEMSS). She has demonstrated the construct validity and reliability of the DEMSS (Strand & McCauley, 2008; Strand, McCauley, & Stoeckel, 2006) She completed an item analysis that will permit the test to be streamlined and will establish the construct validity and reliability of the revised version. Her research will eventually provide normative data so that the DEMSS can be used clinically to aid in differential diagnosis of motor speech disorders in children.
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