Long-Term Speech Outcomes in Moderate-to-Severe Childhood Speech Sound Disorder: A Systematic Review

Parents of children with moderate-to-severe speech sound disorder presenting to clinic want to understand prognosis for their child; however, there is unclear evidence as to the specific long-term speech outcomes in this group.

To review long-term speech outcomes in children with moderate-to-severe speech sound disorders.

A systematic review identified 3697 papers; 21 papers containing 15 unique studies (six had overlapping data) met inclusion criteria for moderate-to-severe speech sound disorder with at least one follow-up speech assessment unrelated to intervention outcomes. Studies were appraised for quality.

Overall, 9 cohort studies, and 6 case studies of children aged 2y3m-to-11y9m at initial assessment were included. Most (11/15) had two-to-three follow-up time points, and 80% (12/15) specified speech diagnosis or subtype. The most prominent moderate-to-severe speech diagnosis that reached criteria for inclusion was Childhood Apraxia of Speech. Speech outcomes reported in case studies included word (7/15), syllable (7/15), consonant (11/15), and vowel (5/15) accuracy, phonological patterns (9/15, prosody (2/15), consistency (1/15), and intelligibility (2/15). Case studies revealed reduced error frequency and improved single-word accuracy and intelligibility, but persistent error types over time (e.g. token-to-token inconsistency). Cohort studies mostly reported on overall gross improvement, such as 'resolved' or 'persistent' disorder; however, the severity of the 'persistent' subgroup was not delineated. Study quality was generally good, with limitations mostly related to confounding factors such as influence of therapy, or poor or absent specification of the specific speech subtype at time zero.

While case studies indicated reduced error frequency over time, larger-scale data are needed to confirm findings. In the current context of health service demands for speech therapy, longitudinal speech outcome data, measuring meaningful speech outcomes are critically needed to identify predictors of longer-term outcomes and inform prioritisation for treatment.

What is already known about this subject Despite mounting evidence on the prognosis and history of mild-to-moderate speech and language disorder, longitudinal cohort studies of children with moderate-to-severe speech sound disorders are rare. This gap is notable given emerging data that severe speech sound disorders are more pervasive and pose greater risk to academic achievement and mental health. What this paper adds to existing knowledge There are no larger cohort studies with clear granular data from which to draw conclusions. Longitudinal case studies show reduced error frequency but persistent error type in children and adolescents with childhood apraxia of speech. There are no cohort studies addressing longitudinal data for other severe speech sound disorders, such as dysarthria or fluency disorders. What are the potential or actual clinical implications of this work? Longitudinal prospective data, with a pre-established goal to systematically evaluate speech outcomes over time in a severe speech cohort, are critically needed to identify accurate predictors of longer-term outcomes and inform treatment prioritisation for children with severe speech sound disorders.