Primary progressive apraxia of speech a distinct neurodegenerative syndrome
Apraxia of speech (AOS) is a disorder of speech motor planning or programming that affects the sequencing of sounds in syllables and words. It often results from left-hemisphere stroke where it rarely progresses and may even improve over time. But AOS can also occur in neurodegenerative diseases — commonly in conjunction with aphasia. Then it is associated with slow onset and progressive loss of speech production, with some patients eventually becoming mute.
AOS can be difficult to distinguish from aphasia — a syndrome characterized by a problem with the use of words rather than their formation — and is often overlooked or ignored in patients who receive an aphasia diagnosis. AOS can also be confused with dysarthria, which arises from a disruption of the neuromuscular control of speech rather than the inability to generate motor programs for speech movement.
Despite similarities among the various disorders, Mayo Clinic researchers have shown that AOS is a distinct syndrome — called primary progressive apraxia of speech (PPAOS). It differs from primary progressive aphasia and can be the sole presenting sign of neurodegenerative disease. Their findings appeared in the May 2012 issue of Brain.
Features of apraxia of speech*
- Slow overall speech rate†
- Lengthened intersegment durations between sounds, syllables, words or phrases; possibly filled, including intrusive schwa†
- Increased sound distortions or distorted sound substitutions with increased utterance length or increased syllable and word articulatory complexity
- Syllable segmentation within words greater than one syllable†
- Sound distortions†
- Syllable segmentation across words in phrases and sentences†
- Audible or visible articulatory groping; speech initiation difficulty; false starts and restarts‡
- Lengthened vowel or consonant segments or both†
- Distorted sound substitutions
- Deliberate, slowly sequenced, segmented or distorted (including distorted substitutions) speech sequential motion rates in comparison with speech alternating motion rates‡
- Increased sound distortions or distorted sound substitutions with increased speech rate
- Distorted sound additions (not including intrusive schwa)
- Sound or syllable repetitions
- Sound prolongations beyond lengthened segments‡
- Inaccurate (off-target in place or manner) speech alternating motion rates, as in rapid repetition of "puh puh puh"‡
Reduced words per speech breath group relative to maximum vowel duration
*Features are ordered from most to least prevalent among the subjects in this study. Features one through five were present in all 12 subjects. All features were present in at least one subject. Note that both prosodic and articulatory abnormalities are captured in several of the listed features.
†Can also be present in spastic dysarthria (only two subjects had unequivocal spastic dysarthria)
‡Can also be present in aphasia, but none of the 12 subjects was otherwise aphasic
For the study, investigators recruited 37 patients presenting at Mayo Clinic's campus in Rochester, Minnesota, with a neurodegenerative speech and language disorder between 2010 and 2011. All underwent speech and language, neurological, and neuropsychological evaluations as well as neuroimaging analysis, including head magnetic resonance imaging and fluorodeoxyglucose positron emission tomography scanning.
Based solely on speech and language tests, 12 patients were found to have AOS without aphasia — the main criterion for PPAOS. The consensus diagnosis was made by two doctoral-level speech language pathologists.
Although the patients had no other neurological deficits in common, all showed gray and white matter volume loss in the premotor cortex and supplementary motor area, and some also showed hypometabolism in those regions.
Mary M. Machulda, Ph.D., L.P., a neuropsychologist at Mayo Clinic's campus in Rochester, Minnesota, stresses the importance of a multidisciplinary research group in understanding the different aspects of neurodegenerative speech and language disorders.
"Unfortunately, there are no treatments or disease-modifying agents for these disorders, most of which will eventually contribute to decline. But to develop therapies, we must understand the underlying pathology," she explains. "Furthermore, once we have an educated diagnosis, we can take steps to plan accordingly and develop creative strategies for working around speech loss. Speech and language disorders can be devastating; people can become mute. But once the problem is identified, there is often relief. It doesn't change the outlook, but patients find it somehow empowering to know what's wrong, especially if they have been misdiagnosed elsewhere."
For more information
Josephs KA, et al. Characterizing a neurodegenerative syndrome: Primary progessive apraxia of speech. Brain. 2012;135:1522.