Speech treatment in nemaline myopathy: A single-subject experimental study

The objective of this work was to verify the efficacy of a treatment based on myofunctional therapy techniques which aimed to improve the tongue strength, precision, and speed of a ten-year-old girl with nemaline myopathy (NM) and the repercussions of this therapy on her speech intelligibility. NM is a rare congenital muscle disorder that causes extreme muscle weakness, especially in the face and neck, as well as severe dysarthria and dysphagia, although this does not affect the nervous system or cognitive development.

This was a single-subject experimental study which used an interrupted pre- and post-treatment time-series design, and which applied autoregressive integrated moving-average predictive models and Holt exponential smoothing. During the treatment phases, the participant's tongue strength and the rate of speech diadochokinesia and voluntary lingual movements were estimated and the repercussions of the intervention in terms of speech intelligibility were ascertained via an experiment with 'naïve' judges.

The treatment produced a sustained and significant increase in the maximum strength of the patient's tongue, which increased from an initial 4 kPa to 11 kPa at the end of the treatment phase. However, this was far from the average 58 kPa for age- and sex-matched normative data. There were no significant changes either in the rates of voluntary lingual mobility or speech diadochokinesia. Speech intelligibility, as assessed by naïve judges, improved from 40 % in the pre-treatment phase to 67 % in the post-treatment phase.

NM and other rare primary muscle disorders allow us to estimate the effects of severe muscle weakness in people with dysarthria without cognitive impairment or alterations in central nervous system, peripheral nervous system or in gap junction. In this case, the treatment did not increase the patient's lingual and articulatory movement speed but did increase her tongue strength from 5 % to 10 % of the levels otherwise expected for her age and significantly improved the intelligibility of her speech and communication.