Speech disorders are one of the most common manifestations of ALS and a real challenge for both clinicians and researchers . Early dysarthric symptoms occur sporadically and usually come in the form of hoarseness and declined speech at the end of the day. As the disease progresses, the symptoms become more severe - the muscles of the tongue, lips and larynx get weaker and slower, their movement amplitude decreases and speech intelligibility declines .
Some researchers argued that speech impairment in ALS is more prevalent in females . Our study did not confirm the finding. We found that it was the male subjects who were affected by speech deficits more often (60.31%) than women. However, the difference was statistically insignificant and requires further in-depth studies to draw further conclusions.
Tongue dysfunction is commonly considered as one of the typical symptoms of speech deterioration in an early stage of ALS . Other symptoms include a decline in the functionality of the soft palate, larynx and lips [36-37].
Among the participants of our study who presented mild speech impairment established by means of the FDA scale, the most prevalent abnormalities were observed in tongue mobility (63.2%), soft palate (70%) and lips (72.5%). The obtained results correspond with the current state of knowledge on the subject [36-37].
The main measure of communication efficiency in ALS subjects is the extent to which their speech is intelligible. Impaired speech undoubtedly affects quality of life and the severity of communication deficit is a determinant of the treatment option that ought to be applied . Speech intelligibility could be treated as a practical measure used in monitoring the quality of articulation during the course of treatment as well as the assessment of the progression of the disease process .
Yunusova et al. demonstrated the existence of a direct relationship between speech intelligibility and the mobility of the lips and jaw in ALS subjects . Other researchers reported lack of correlation between speech comprehension in ALS and progression of the disease . It has also been found that in the early stages of the disease the reduced mobility of the tongue, lips and jaw does not affect speech intelligibility . A considerable deficit in this respect, though, can be observed with the emergence of signs of critical laryngeal dysfunction .
Our study shows that the ALS patients presenting mild impairment of the articulatory system, measured using the objective FDA scale, do not perceive significant deterioration of speech intelligibility, established by means of the subjective VHI. It is not until the occurrence of a considerable decrease in the articulators efficiency that a substantial decline in speech becomes evident. We found that a speech intelligibility decline coincides with dysfunctions in the length of phonation, pitch and voice volume. Also, the study revealed the existence of a correlation between FDA-based assessment of speech deterioration and the patient’s perception of a decline in the physical and functional aspects of everyday life established by means of the VHI. These findings provide a valuable contribution to the knowledge of ALS progression and its impact on life quality of ALS sufferers.
Existing research does not mention any relationship between a progressive deterioration of motor functions and disorders of emotional nature . Some earlier publications noted ‘the disability paradox’ phenomenon, a term that refers to the alleged lack of relationship between the subjective perception of physical dysfunction reported by ALS patients and a decline in quality of life [43-44]. Others, on the other hand, pointed to a weak or moderate correlation between the disease severity and the emotional condition of the sufferer . The latter pattern was reflected in our study – the participants complained of a depressed mood they experienced in line with the progression of speech deficits.
The progression of speech deterioration in ALS is very rapid, which is reflected by the fact that the median survival for the disease is merely 30 months . It is therefore vital that the process of speech deterioration should be monitored in a clinical setting so that new communication strategies could be devised and introduced in time. However, the range and reliability of currently available instruments for adequate monitoring of the articulatory functions is still insufficient. The limitations mainly concern the number of factors affecting the accuracy of the relevant examinations, their validity and reproducibility. Normalized diagnostic procedures applied for the evaluation of articulation quality and monitoring speech regression in ALS are very scarce . This can be attributed to the logistic difficulty connected with the analysis of bulbar symptoms. Shortages of proper tools for the assessment and monitoring of speech deterioration are commonplace in clinical environment. The procedures in most instances require the employment of sophisticated instruments such as tensometric sensors or air pressure bulbs, whose reliability and precision are yet to be properly documented [39, 47]. One of the earliest predictors of ALS progression is a decline in the movement velocity of the articulatory organs .
The tools that we applied in our study to monitor the efficiency of the articulators and speech intelligibility comprised the FDA and the VHI rating scales. The analysis of the relationship in respect to the entire cohort demonstrated positive moderate correlation in 5 domains and high correlation in another 8 ones. Regarding the relationship between the FDA and the physical subscale of the VHI a very strong positive correlation was found in 9 articulatory domains and high correlation in 4 others. The scores the emotional subscale of the VHI provided showed a very high positive correlation in 6 domains and high correlation in 7 domains, while in the case of the functional component scores the relevant numbers of domains were 7 and 6 respectively. In terms of correlation with the division into groups, group I showed a high positive correlation in 5 articulatory domains and in 7 others the positive correlation was of an average intensity. As for group II, a very high positive correlation was observed in one domain, high in 8 and average in another 3 domains. Summarizing, the extent of a decline in the performance of the articulatory organs established by an experienced researcher corresponded with the patient-reported self-assessment of speech comprehensibility. These findings were substantially different from the outcomes of another study we carried out on the subjective and objective assessment of the extent of articulatory disorders in PD patients . It may be the case that Parkinsonian patients are well-adjusted to the changes in the articulatory system. It needs to be noted that the average duration of Parkinson's disease is 15.8 years  compared to 30 months in the case of ALS . Consequently, a dramatic speech deterioration in ALS is observed within a significantly shorter space of time. The results of this study imply that the VHI could be used as a reliable self-applied instrument for monitoring the course and progression of speech impairment in ALS as well as a prognostic instrument for predicting the progression of speech deterioration, which apart from being an early marker of acute speech exacerbation , is of critical importance in the context of therapeutic procedures for ALS. In the light of the abovementioned facts, it can be assumed that the VHI is a reliable marker of speech decline in ALS and thereby a useful tool for the verification of the onset of the symptoms and their progression, which will ultimately help to introduce proper therapeutic strategies. The application of a regular, cyclical examination of speech function using a self-assessment tool (VHI questionnaire) would have many advantages, i.e. the possibility of self-conducting a home examination, reducing the number of visits to a specialist with cost limitation, rapid screening of patients with deterioration of articulation requiring specialist assessment and treatment.