Apraxia of speech and cerebellar mutism syndrome: a case report

Abstract

BackgroundCerebellar mutism syndrome (CMS) or posterior fossa syndrome (PFS) consists of a constellation of neuropsychiatric, neuropsychological and neurogenic speech and language deficits. It is most commonly observed in children after posterior fossa tumor surgery. The most prominent feature of CMS is mutism, which generally starts after a few days after the operation, has a limited duration and is typically followed by motor speech deficits. However, the core speech disorder subserving CMS is still unclear.Case presentationThis study investigates the speech and language symptoms following posterior fossa medulloblastoma surgery in a 12-year-old right-handed boy. An extensive battery of formal speech (DIAS = Diagnostic Instrument Apraxia of Speech) and language tests were administered during a follow-up of 6 weeks after surgery. Although the neurological and neuropsychological (affective, cognitive) symptoms of this patient are consistent with Schmahmann’s syndrome, the speech and language symptoms were markedly different from what is typically described in the literature. In-depth analyses of speech production revealed features consistent with a diagnosis of apraxia of speech (AoS) while ataxic dysarthria was completely absent. In addition, language assessments showed genuine aphasic deficits as reflected by distorted language production and perception, wordfinding difficulties, grammatical disturbances and verbal fluency deficits.ConclusionTo the best of our knowledge this case might be the first example that clearly demonstrates that a higher level motor planning disorder (apraxia) may be the origin of disrupted speech in CMS. In addition, identification of non-motor linguistic disturbances during follow-up add to the view that the cerebellum not only plays a crucial role in the planning and execution of speech but also in linguistic processing. Whether the cerebellum has a direct or indirect role in motor speech planning needs to be further investigated.

Evidence for Reciprocal Structural Network Interactions Between Bilateral Crus Lobes and Broca’s Complex

“…In addition to cerebellar internal models related to language mainly stored in the right posterolateral cerebellum as mentioned above, many recent studies demonstrated a division of labor for phonological, syntactic, and semantic planning in Broca's complex (Flinker et al, 2015;Glasser et al, 2016;Long et al, 2016;Belyk et al, 2017;Giahi Saravani et al, 2019;Klaus and Hartwigsen, 2019). If verified, the existence of reciprocal structural connections between bilateral Crus lobes and Broca's complex would (1) give credible evidence to support a direct role of the bilateral cerebellums in motor speech planning and (2) explain why AoS can occur in patients with etiologically heterogeneous cerebellar disorders (Marien et al, 2006;De Smet et al, 2007;Marien and Verhoeven, 2007) and after pediatric MB surgery (De Witte et al, 2017). In the latter case, damage of efferent cerebellar pathways, such as part of the Crus-Broca tracts, would give rise to AoS due to defect of output of cerebellar internal models predicting and consequently optimizing phonological planning and execution (Marien and Manto, 2018).…”

“…The clinical imaging of patients with cerebellar disorders has revealed a broad range of motor speech impairments in terms of both execution and planning (Marien et al, 2006;De Smet et al, 2007;Marien and Verhoeven, 2007;Korah et al, 2010;Di Rocco et al, 2011;De Smet et al, 2013;De Witte et al, 2017). Several studies have found that cerebellar internal models, mainly in the right posterolateral cerebellum, transmit predictions on coming 'non-motor' information in several linguistic processes of phonology, semantics, syntax, and others (Miall et al, 2016;Runnqvist et al, 2016;D'Mello et al, 2017;Lesage et al, 2017).…”

“…Although residual speech dysfunction after CMS is frequently defined as ataxic dysarthria, there is no consensus on the exact nature of the motor speech pathology underlying CMS (Korah et al, 2010;De Witte et al, 2017). In addition to deficits in motor speech execution, a variety of concomitant motor speech planning disturbances may manifest after alleviation of mutism, such as impaired verbal initiation, agrammatism, disrupted language dynamics, comprehension deficits, and reading and writing disorders (Di Rocco et al, 2011;De Smet et al, 2013).…”

“…In addition to deficits in motor speech execution, a variety of concomitant motor speech planning disturbances may manifest after alleviation of mutism, such as impaired verbal initiation, agrammatism, disrupted language dynamics, comprehension deficits, and reading and writing disorders (Di Rocco et al, 2011;De Smet et al, 2013). De Witte et al (2017) reported only apraxia of speech (AoS) rather than ataxic dysarthria after pediatric MB surgery. AoS, which is defined as a dysfunction of both motor speech planning and programming, not only arises from injury to cerebral languagedominant motor speech regions (e.g., Broca's area) (Dronkers, 1996;Hillis et al, 2004;Ottomeyer et al, 2009;Chang et al, 2015) but has also been observed in a number of cases of etiologically heterogeneous cerebellar disorders (Marien et al, 2006;De Smet et al, 2007;Marien and Verhoeven, 2007).…”

Right cerebral motor areas that support accurate speech production following damage to cerebellar speech areas

“…For example, an epidemiological study of cerebellar stroke found that around 40% of patients with cerebellar damage showed signs of dysarthria upon examination early after stroke, suggesting the involvement of the cerebellum in articulation ( Tohgi et al, 1993 ). There is also evidence that cerebellar damage can cause apraxia of speech ( De Witte et al, 2017 , Mariën et al, 2015 ), which according to Mariën et al (2015) might have similar underlying motor planning difficulties as ataxic dysarthria. A key observation, first noted by Holmes (1917) more than a hundred years ago and endorsed by others ( Schmahmann and Sherman, 1998 ), is that a large proportion of patients with cerebellar stroke have speech production impairments that recover completely within the first few months after insult.…”