Over the years, since the first accounts of the disorder, there has been disagreement over the underlying nature of the disorder. Some have proposed that CAS is linguistic in nature; others have proposed that it is motoric and some have put forth the tenet that it is BOTH linguistic and motoric in nature. However, currently nearly all sources describe the key presenting impairment involved with CAS as some degree of disrupted speech motor control. The reason for this difficulty is still under investigation by speech scientists.
Weakness, paresis, or paralysis of the speech musculature does not account for the impaired speech motor skills in CAS. Differences in various theories of speech motor control notwithstanding, it is believed that the level of impairment in the speech processing system occurs somewhere between phonological encoding and the motor execution phase, such as a disruption in motor planning and/or programming. Some believe that children with CAS have difficulty accurately storing or volitionally accessing speech motor plans and programs and the spatial-temporal specifications within them. To some degree or another, these impairments result in difficulty rapidly and accurately moving between sequences of articulatory configurations that are required for continuous and intelligible speech production. Some researchers posit that children with CAS additionally have disordered sensory-motor related features such as reduced or aberrant proprioception and thus an inability to realize the relationship and spatial position of the articulatory structures to one another. For some of the most severely affected children, even initiating speech movement gestures may prove extraordinarily difficult.
While CAS shares some features with adult acquired Apraxia of Speech, there are also key differences. Perhaps the biggest challenge of all is to understand the presumed effects of faulty motor speech control processes on the child’s developing speech processing system. In adult AOS, an assumption exists that the individual has an intact speech processing system. Exactly how CAS affects the developing speech processing system of affected youngsters remains to be seen. Presumably, however, there are reverberations and consequences throughout the system because of the speech motor deficits.
There appears to be some consensus and research evidence that children who display these sorts of speech motor impairments also typically have problems in certain aspects of expressive and/or receptive language, even if subtle. Reportedly, “pure” apraxia of speech in children is rare. There is currently no agreement as to whether these linguistic impairments are central to the disorder or are separate issues that co-occur or are co-morbid. Some individuals have described CAS as a disorder that changes and unfolds over time.
Again, research is lacking in providing us with information regarding both incidence and prevalence figures. The estimates of some sources indicate that CAS is low incidence with perhaps 1 – 10 in 1000 children affected or 3 – 5 % of speech-impaired preschoolers. In addition, some believe that the incidence of CAS may have increased in recent years. However, there are no published scientific data to support this general sense of increased incidence.