techniques to treat individuals diagnosed with dysarthria. Thus, this paper will specifically discuss the prominent characteristic of weakness sometimes found in oro-motor structures of individuals with dysarthria, investigate its effects on speech intelligibility, and briefly consider research supported therapy techniques specific to oro-motor weakness.
Speech intelligibility is the degree in which a speaker can be understood. In order for a speaker to be considered intelligible, he/she needs to produce adequate speech sounds, form sentences in the correct syntax, display prosody, demonstrate topic maintenance, and have the physical skills required to produce fluent sentences (Flipsen, 2010). SLPs determine the level of speech intelligibility of an individual during evaluations. Often times an individual will have higher intelligibility when speaking to a familiar listener such as a parent or caregiver or when there is a shared understanding of the conversational topic between the speaker and the listener (Eadie, Otero, Bolt, Kapsner-Smith, & Sullivan, 2016). Regardless, the degree of speech intelligibility is measured by the percentage of time in which the speaker is understood (Eadie et al., 2016). Low speech intelligibility is present when there is a disruption in one or more areas of speech or language including lip and jaw movements for articulation, syllable repetitions during alternating motion rates (AMRs), nasal emission, maximum phonation time (MPT), and number of speech breaks/pauses as a result of breath support (Rong et al., 2016). Therefore, low speech intelligibility may be a result of weakness within the oro-motor structures affecting articulation.
To begin to understand the relationship between weakness and decreased speech intelligibility, it is essential to first define weakness and understand it’s underlying neuropathology. According to Ramdharry (2010), weakness is defined as “a reduction of strength in a muscle that is unable to produce sufficient force for a desired task or motion”(p. 338). This lack of adequate force is caused by damage, as a result of injury or disease, to the lower motor neurons specifically within the anterior horn, the peripheral nerves, the cranial nerves, the neuromuscular junction, and/or the muscle itself (Ramdharry, 2010). Damage to one or more of these areas results in the inactivation or reduction of the lower motor neurons’ muscle input, thus exacerbating the muscles’ contract-constrict sequence resulting in varied degrees of weakness or complete paralysis of the muscle (Duffy, 2013, p.96). In addition, weakness is commonly paired with atrophy, the wasting away of muscle tissues, and increased levels of fatigue, which may be caused by the excessive overworking of muscles in an attempt to compensate for lost strength beyond the muscles reserve (Ramdharry, 2010). Hence, increased levels of fatigue, also known as fatigability, are typically found when individuals with weakness as a result of lower motor neuron disease or injury, continuously activate the weakened muscles to perform a necessary or desired activity (Ramdharry, 2010).
Due to the strong correspondence between weakness and motor neuron damage, professionals evaluating individuals who have suffered from injury, illness, or disease affecting the neurological system, frequently examine and describe the type and degree of weakness to assist in differential diagnosis (Statland, Barohn, McVey, Katz, & Dimachkie, 2015).
When examining weakness, professionals may choose to complete subjective measures, objective measures, or a combination of the two in order to thoroughly describe weakness and its characteristics to assist in the diagnostic and treatment planning process. One way of subjectively describing weakness that is commonly part of speech-language evaluations is an oral mechanism examination. There are a variety of oral mechanism examinations that an SLP can complete, ranging from informal measures such as checklists, to formal measures such as the Oral Speech Mechanism Screening Examination (OSMSE). Regardless of the method used, all oral mechanism examinations evaluate the oral structure, non-speech oral motor function, and speech motor functions, which are essential when describing the location, degree, and impact of weakness on the oral structure and motor functioning (McCauley & Strand, 2008). Professionals may also use objective measures to describe weakness by analyzing specific patterns of weakness and defining them according to 10 different patterns described by Statland et al. (2015). Statland et al. (2015) stated that when …show more content…
analyzing weakness patterns, one must first determine which parts of the motor system is affected (e.g. motor, sensory), where the weakness is located, if the weakness is distal/proximal or symmetric/asymmetric, time since onset, and motor involvement. Once this information about weakness has been determined, professionals on health care teams can then categorize weakness within one of 10 patterns to determine the location of the lesion that is causing weakness (Statland et al. 2015). Hence, when evaluating weakness, it can be beneficial to use a combination of both subjective and objective measures to allow for a comprehensive assessment to further assist in differential diagnosis.
Once weakness has been identified, the SLP can determine its effects on speech intelligibility and determine the motor speech diagnosis present.
There are many types of motor speech disorders, however, weakness is commonly associated with certain types of dysarthria. Specifically, researchers studying various dysarthria types have found that weakness is strongly associated with the diagnosis of flaccid dysarthria (Boone, McFarlane, Von Berg, & Zraick, 2014). In fact, while researchers Murdoch and Chenery (1990) performed a case study to investigate structural changes in the brain as a result of radiation to reduce brain tumors, they gathered much information to support how weakness in flaccid dysarthria can affect speech intelligibility. In the study, a 39 year-old-woman was evaluated after having radiation and surgery to remove a tumor within the pituitary fossa (Murdoch & Chenery, 1990). After radiation, the family reported deterioration in the woman’s speech as they stated that she had become much harder to understand. Hence, a speech evaluation was conducted in which the researchers discovered that the woman had flaccid dysarthria classified by slow tongue movements, reduced elevation of the velum resulting in hypernasality, poor respiratory support, and imprecise articulation as a result of weakness (Murdoch & Chenery, 1990). These findings were preceded by a neurological evaluation that found damage to the Xth cranial nerve (Murdoch & Chenery, 1990). This
provides neuropathological evidence that weakness as a result of lower motor neuron damage, which includes damage to the cranial nerves, can in fact result in poor speech intelligibility.
In addition to flaccid dysarthria, weakness is also commonly found in individuals with dysarthria attributed to unilateral upper motor neuron (UUMN) damage (Hartman & Abbs, 1992). While there is less information known about UUMN dysarthria in relation to other dysarthria types, researchers have found that weakness is the primary characteristic of the dysarthria as a result of lesions within the pyramidal tract including the motor cortex, the cell bodies, and/or the axons that affect motor movements, most often a result of a cerebral vascular incident (CVA) (Hartman & Abbs, 1992). In fact, researcher Hartman and Abbs (1992) conducted a study on six adults whose CT scans revealed unilateral lesions within the upper motor neurons, as a result of a CVA, and found signs of weakness in all of the participants. Specifically, the researchers reported weakness within structures essential for speech production including the tongue and the face, as well as structures such as limbs, which are important for participating in life activities (Hartman & Abbs, 1992). In addition, researchers Hartman and Abbs (1992) found that all six of the participants had dysarthria characterized by low speech intelligibility ratings when completing diadochokinetic speech samples, verbally producing words in isolation, reading The Grandfather Passage, and describing The Cookie Theft Picture when reading and speaking to unfamiliar listeners. The three SLPs who analyzed the participants’ speech, via a perceptual analysis, an oral mechanism examination, and electromyography, described the participants’ low speech intelligibility readings to be a result imprecise articulation due to reduced tongue, lip, and jaw strength (Hartman & Abbs, 1992). Thus, this information further demonstrates the impact of weakness within the oro-motor structures on speech intelligibility when present in dysarthria.
All things considered, research has supported that when lesions occur within either lower motor neurons or unilaterally within the upper motor neurons, it is likely that dysarthria will occur in conjunction with weakness. This information is specifically important when considering how weakness can affect the oro-motor structures including the lips, jaw, tongue, cheeks, and velum (McCauley & Strand, 2008). Weakness in the lips, tongue, jaw, cheeks, and velum inhibits proper movement needed to articulate speech sounds. Hence, the decreased movement of the oro-motor structures results imprecise articulation, which in turn decreases the individuals speech intelligibility. Therefore, as SLPs treating this population, it is essential to have the knowledge needed for differential diagnosis and to perform individualized treatment to improve or compensate for decreased speech intelligibility.