Stuttering (Stammering)

Etiology

Stuttering can be broadly conceptualized as having either a developmental or an acquired etiology.[2] 

Developmental Stuttering

This form of speech disfluency is the most prevalent type and occurs in young children during the critical period while they are still developing their speech and language abilities. One theory suggests that developmental stuttering arises when a child's speech and language skills fail to meet their verbal demands. Genetic conditions, such as Prader-Willi syndrome, Down syndrome, and Fragile X syndrome, have also been associated with stuttering, where the stuttering pattern is phonologically similar to the developmental variant.[10] Conversely, acquired stuttering emerges later in life, often stemming from various underlying etiologies.[2] 

Acquired Stuttering

Acquired stuttering can be further categorized into neurogenic, psychogenic, and drug-induced causes. Alternatively, some classification systems distinguish stuttering into psychogenic and organic origins, where the latter category comprises developmental, neurogenic, and drug-induced stuttering. 

Neurogenic stuttering: Neurogenic stuttering arises from damage to specific brain tissue regions due to an insult.[2] Potential causes of such damage or injury include stroke (the most prevalent), significant traumatic brain injury, hypoxic-ischemic encephalopathy, various dementing diseases, Parkinson's disease, sequelae of dialysis, corticobasal ganglionic degeneration, multiple sclerosis, and epilepsy.[2][11][12][13][14][15] Consistent with various injury mechanisms, neurogenic stuttering exhibits variability in its underlying neural substrates and does not distinctly localize to a specific brain region. Commonly affected areas include the bilateral hemispheres, subcortical white matter tracts, the cerebellum, and deep nuclei such as the basal ganglia, thalamus, and brainstem. Notably, the left hemisphere, typically dominant for language, is more commonly affected than the right hemisphere.[16]

Psychogenic stuttering: Psychogenic stuttering is classified as a functional disorder, a modern term for what was previously known as conversion disorder, where psychological symptoms manifest as physical ones. This condition is among the various functional speech and voice disorders.[4] For stuttering to be deemed psychogenic, changes in spoken patterns must be connected to an underlying emotional conflict and lack an identified so-called organic etiology. In addition, psychogenic stuttering usually co-occurs with other mental health issues and lacks a consistent emotional response to stuttering across different situations.[17]

Pharmacological stuttering: Pharmacological stuttering arises as a result of the administration of certain pharmacological agents. Pharmacological mechanisms that can predispose to stuttering include increased dopamine levels, decreased GABA levels, medications with anticholinergic properties, and drugs affecting serotonin levels. Interestingly, while some medications may induce stuttering in certain individuals, they might alleviate it in others. Disproportionately high instances of stuttering have been reported with stimulants such as lisdexamfetamine, dexamphetamine, and methylphenidate, antidepressants such as duloxetine, fluoxetine, dosulepin, and bupropion, anti-seizure medications such as pregabalin, topiramate, brivaracetam, and gabapentin, as well as montelukast, asenapine, and guanfacine.[18]

Genetic factors, particularly in developmental stuttering, have been the subject of research for decades. Until recently, only a few genes have been identified, including GNPTAB, GNPTG, NAGPA, and AP-4. These genes encode proteins related to the lysosomal enzyme-targeting pathway and were initially identified in consanguineous families. While these genes are involved in intracellular trafficking, they collectively account for less than 20% of persistent stuttering in unrelated individuals.[19] Recent whole exome sequencing performed in a family with autosomal dominantly inherited stuttering has revealed a novel missense polymorphism at a proline residue (p.P270S) within a functional domain of the CYP-40 protein encoded by the PPID gene.[20] While further investigation is needed, this variant of CYP-40, integral to the functionally crucial chaperone machinery of heat shock proteins, may yield novel stuttering pathomechanisms associated with this protein and others performing molecular chaperone functions.[21]

Epidemiology

Stuttering is a relatively common condition with a global prevalence of around 80 million and poses a significant challenge for healthcare providers.[18] The incidence of stuttering varies depending on its underlying etiology.

Developmental stuttering: This condition is also referred to as childhood-onset fluency disorder and is the most prevalent form of stuttering. Development stuttering predominantly affects children aged 2 to 6, with an estimated 5% to 10% of preschoolers affected. Although the most consistently reported lifetime incidence is 5%, recent data suggest a higher incidence nearing 10%.[18][22] Many cases of developmental stuttering resolve eventually, but about 1% of adults live with persistent stuttering.[6][23]

Neurogenic stuttering: Epidemiological data on neurogenic stuttering remain incomplete, and the majority of published studies primarily consist of single case reports or small case series.[11][24][25] Although, generally, the incidence of neurological stuttering is generally believed to be low, apparent discrepancies between reported incidences and clinical observations challenge its perceived rarity.[26][27][28] General consensus was obtained that neurogenic stuttering is more frequently observed in adults and disproportionately affects men, with reported gender ratios ranging between 2:1 and 10:1.[29]

Psychogenic stuttering: This condition exhibits a much closer sex ratio parity than neurogenic stuttering, in contrast to organic stuttering, where men significantly outnumber women (3:1, respectively). According to a study, stuttering-like disfluencies were the second most frequently reported functional speech disorder, following only functional dysphonias.[30] Functional speech disorders often co-occur with functional movement disorders, with stuttering being one of the most common functional speech disorders reported in this subset of patients.[31]

Pharmacological stuttering: This form of stuttering is exceptionally rare. An analysis of the World Health Organization's global individual case safety reports database (VigiBase) revealed a cumulative incidence of only 724 cases worldwide as of May 2020.[3]

Pathophysiology

The exact mechanisms underlying developmental stuttering remain incompletely understood. However, a consensus exists that stuttering arises from a complex interplay of linguistic, motoric, and emotional factors, interacting in nonlinear ways.[6] Overall, it is generally believed that stuttering results from defects in the brain regions responsible for speech planning, coordination, and execution, with individual variations in the specific abnormalities observed.[6][23][7][32] The cumulative effect of these impairments, along with environmental and genetic influences, determines the severity and likelihood of recovery.[6] 

Functional neuroanatomical changes observed in individuals who stutter include:

Abnormal integration of sensory and motor functions during speech production: This is characterized by diminished white matter integrity in areas of the dorsal auditory tract, particularly the left arcuate or superior longitudinal fasciculus. This tract is responsible for connecting auditory and speech motor areas such as the ventral premotor cortex, posterior superior temporal gyrus (Wernicke area), ventral motor cortex, and inferior frontal gyrus (Broca area). These regions may exhibit structural and functional differences in people who stutter.[33] 

Abnormal temporal coordination and arrangement of speech sounds: The delicately balanced timing required for fluent speech may be disrupted due to a lack of coordination between cortical and subcortical regions.[34][35]

Aberrant laterality of the brain: Aberrant laterality of the brain can occur in neurogenic stuttering, with specific pathologies leading to lesions in varying locations depending on the nature of the insult.[36] 

Neurotransmitter disturbances: Various pathophysiological mechanisms have been postulated to contribute to drug-induced stuttering; however, further research is needed in this domain. Proposed mechanisms include elevated cerebral dopamine levels, alterations in the acetylcholine or dopamine balance, GABA depletion, and changes in serotonin levels.[18][37][38]

History and Physical

Thorough history-taking and a specialized clinical evaluation focused on stuttering are essential tools for clinicians to identify the characteristics of stuttering and its associated behaviors. These evaluations are particularly crucial in distinguishing between different stuttering etiologies.

Clinicians should seek the following characterizations when assessing developmental (and persistent) stuttering: 

• Blockades and other disfluencies often occur at the beginning of utterances.[2][39]
• Improved fluency with repeated reading of the same material, known as the "adaptation effect."[40]
• Reduction or elimination of stutters when singing or speaking in unison with others, known as the "choral effect."[41] 
• Increased likelihood of stuttering with greater sentence complexity and length.[39]
• Development of secondary behaviors associated with stuttering.
• Adverse emotional reactions related to stuttering and secondary behaviors.

Persistent stuttering can lead to the development of secondary behaviors, such as grimaces, jaw jerks, and head movements, which individuals use to mitigate the severity of stuttering. However, adverse reactions to these secondary behaviors can further distress people who stutter.[42] Clinicians should remain vigilant for these behaviors during clinical evaluations, recognizing that they may induce stress in individuals who stutter.

Acquired stuttering typically presents with a sudden onset due to an injury or other acute event (neurogenic stuttering), or it may arise as a manifestation of one or more psychological processes (psychogenic stuttering). Acquired stuttering can develop at any age.[18]

An acute neurological event typically precedes neurogenic stuttering. The period between the inciting insult and the onset of symptoms varies, ranging from nearly immediate to several months after the insult. However, the onset of symptoms is almost always sudden. Concomitant symptoms suggestive of an underlying neurological etiology, such as tremors, headache, coordination difficulties, or hemiparesis, can help differentiate neurogenic forms from the other causes of stuttering.[27]

The characteristics of neurogenic stuttering that clinicians should be attentive to include the following:[36][24] 

• Repetition of sounds and syllables
• Blockades, which can appear anywhere in the speech, although less commonly than in developmental stuttering
• Absence of adaptation effects
• Consistency of stuttering across different tasks, such as conversation, reading, and repetition
• Signs of other speech disorders, such as dysarthria along  with stuttering
• Secondary behaviors such as blinking and facial grimaces are rare, and, if they occur, they tend not to be linked to periods of active stuttering
• The stuttering may vex the patient, but prolonged or repetitive speech does not usually cause anxiety.

Characteristics of psychogenic stuttering that clinicians should carefully consider include the following:[30][43] that the astute clinician should seek include the following:

• Abrupt onset
• Consistency of stuttering in different tasks, such as conversation, reading, and repetition
• Disfluencies appearing anywhere in the speech
• Unusual voice quality
• Absence of clinical features suggestive of neurological pathology
• Absence of other communication disorders, such as dysarthria
• Improvement in disfluency after expressing emotional feelings
• Persistence of stuttering in situations or exercises that would typically improve disfluency
• Unusual body movements and features of anxiety independent of speech
• Use of "broken English" patterns, such as "me not well"
• Excessive variability or consistency in stuttering patterns.

The overlap between the clinical presentations of neurogenic and psychogenic stuttering often makes discrimination challenging. Thus, it is crucial to explore any apparent history of emotional distress in patients with psychogenic stuttering as part of the initial history-taking process.

Background information related to stuttering: Stuttering-related background information is obtained through comprehensive history-taking and interviews, including both the individual who stutters and relevant individuals in their lives. In addition, it is essential to explore various domains, preferably through open-ended questions, such as experiences related to stuttering, concerns, and the individual's expectations from treatment.

Background information regarding speech, language, temperament, and other related domains: This can be obtained through various standardized tests, questionnaires, observations, and interviews. Evaluating these aspects is particularly significant in younger children.

Medication review: Obtaining a detailed history of medications is necessary for every patient who stutters, as well as paying close attention to drugs that may impact central nervous system neurotransmitters, as they could indicate potential drug-induced stuttering.[3]

Evaluation

Following comprehensive and relevant history-taking, a thorough evaluation of patients with stuttering includes the use of screening and assessment tools to confirm the diagnosis, identify the underlying etiology, recognize adverse consequences, and understand the patient's concerns, all of which will ultimately guide treatment protocols. In 2021, explicit clinical recommendations based on iterative expert consensus outlined 6 core areas as standard components of a comprehensive evaluation of stuttering and individuals who stutter.[44] 

Clinicians can utilize recommended evaluation tools across various assessment domains, including:

• Case history forms
• Interviews with both the patient and relevant individuals in their life
• Observations of interactions, speech, and fluency in different tasks
• Screening and testing of language and speech development, temperament, hearing, and other pertinent abilities
• Testing and observation of stuttering behaviors, as well as responses to and impacts of stuttering
• Analysis of risk factors

A core set of themes constitutes the framework for stuttering evaluation, which includes:

Stuttering and speech-fluency behavior: Clinicians should evaluate how the speaker stutters and their behavior during stuttering episodes. Given the variability in stuttering behaviors among individuals, assessing speech across various tasks and settings is valuable for accurately understanding the individual's stuttering patterns. Insights from individuals close to the patient can provide additional context regarding the scope and characteristics of the stuttering.[45]

Clinicians should consider patient-based severity ratings, clinician rating scales, standardized tests, and test scores that assess stuttering-specific speech fluency. Useful instruments include the Stuttering Severity Instrument [46] and the Speech Situation Checklist, which incorporates subtests for speech disruption and emotional reaction.[47]

Reactions to and perceptions of stuttering—both by the patient and those in the patient's environment: Stuttering reactions comprise the speaker's responses to their stuttering and how others react. Individuals who stutter may change their behavior or decisions based on their stuttering patterns and perceived reactions from others, which can adversely impact interpersonal interactions and self-confidence. Areas such as anticipation, awareness, coping strategies, and avoidance behaviors should be thoroughly discussed and assessed. Clinicians should delve into reports of bullying and other adverse reactions to stuttering, examining their impact on the individual who stutters. Interviews, observations, and questionnaires can provide valuable insights into these aspects.

Negative consequences associated with stuttering: This domain evaluates the limitations and impact of stuttering on various aspects of a speaker's life, including employment, education, social interaction, and overall quality of life. Valuable evaluation tools include interviews, observations, and standardized tests such as Overall Assessment of the Speaker's Experience of Stuttering (OASES) [48] and Wright and Ayre Stuttering Self-rating Profile (WASSP).[49].

Stuttering assessment, including the tools and procedures utilized, must always be tailored to meet the unique needs and requirements of each patient. The experiences, reactions, and adverse consequences of stuttering, as well as the anticipated benefits from therapy, exhibit significant variability among patients. Therefore, a one-size-fits-all approach is not appropriate.[44][45][46][45] Assessments should conclude with collaboratively established goals and agreed-upon criteria for defining successful therapy outcomes.

A comprehensive neurological examination is essential to exclude neurogenic stuttering. Determining the temporal relationship between stuttering and any suspected neurological insult, as well as reviewing environmental influences, can aid in diagnosing neurogenic stuttering.[27] Motor speech assessment is crucial for identifying concomitant motor speech disorders, which are often present in patients with neurogenic stuttering and should not be overlooked during the examination. Additionally, assessing cognitive abilities may provide further insight into the potential location of underlying brain damage. Imaging studies, such as computed tomography or magnetic resonance imaging scans of the brain, may reveal brain lesions.

Regardless of the underlying cause of stuttering, referral for appropriate psychiatric evaluation and counseling is crucial. This step is essential for preventing potential adverse mental health outcomes and for exploring the possibility of psychogenic stuttering.

Treatment / Management

Treatment protocols should be formulated to address the patient's concerns effectively, ensuring that therapeutic objectives align with the patient's goals. In cases of suspected developmental stuttering, any child exhibiting speech patterns indicative of stutter-like disfluencies, whether reported by parents or observed clinically, should be referred to a speech-language pathologist. Urgency in referral increases if the disfluency persists for 1 year or more or if parental reports indicate worsening severity or increased frequency of stuttering.[50][6][51](A1)

Generally, speech and behavioral therapies are initiated early in children to leverage the plasticity of the nervous system. These therapies aim to facilitate compensatory changes that can lead to normal fluency. Early intervention may help prevent the development of impaired social skills and negative perceptions of communication often observed in individuals with long-standing stuttering.[51][6][52][53][54][55](A1)

For patients who continue to stutter persistently, therapeutic goals typically evolve to include managing secondary behaviors, developing appropriate compensatory techniques, fostering acceptance of stuttering as a natural part of the individual's identity, and reclaiming a sense of command over speech.[56][57][58](A1)

Various types of speech and behavioral therapies are used to address stuttering, each offering potential benefits tailored to the individual's needs and therapeutic objectives and responses.[56] However, medications have not shown effectiveness in managing developmental or persistent stuttering.[59][60](A1)

Stuttering therapy can be categorized as either direct or indirect.[61][50] Indirect therapy focuses on creating environments conducive to fluency-enhancing behaviors while minimizing factors that hinder fluency. In contrast, direct therapy involves working with patients who stutter to enhance speech fluency and address other negative effects of stuttering.[62](A1)

Commonly Used Therapies for Stuttering

The Lidcombe program: This program involves training parents to praise fluent speech and respond appropriately to stuttered speech.[63] Responses are tailored to the child's individual needs and may include initially ignoring the stuttered speech and responding to the content of what the child has said or acknowledging the stutter and prompting the child to repeat the phrase fluently. The Lidcombe program provides a high degree of flexibility in the array of possible responses and accommodates the individual circumstances of the patient and their parents. Regular speech assessments in clinical and home settings help gauge stuttering severity, allowing for ongoing progress monitoring and adjustments to management protocols. Regular follow-up appointments and ongoing support from the clinic are essential even after stuttering diminishes. This ensures that the child continues to maintain fluent speech as the program components are gradually withdrawn. 

The RESTART-DCM treatment: This treatment involves assisting parents in making environmental adjustments to reduce the speech demands placed on the stuttering child. Interventions may include altering parental communication styles or adjusting the overall pace of the child's living environment. Direct interventions such as reducing the child's speech rate or implementing speech drills may also be used if needed.

The Palin PCI treatment: This therapy emphasizes interaction strategies and family-based approaches.[64] Interaction strategies include adapting speech rates to match the child's, allowing the child to take the lead during play, and maintaining good eye contact. Family strategies include promoting turn-taking in conversation, fostering confidence-building activities, and fostering open discussions about stuttering.

The family-focused treatment approach: As described by Yaruss et al,[65] this approach integrates both direct and indirect therapies for preschool children. This treatment includes improving communication and comprehension between parents and children, adjusting parental communication styles, modifying the child's communication patterns, and accepting stuttering.

The Westmead program: This program focuses on syllable-timed speech to aid individuals who stutter in achieving fluency by rhythmically vocalizing each syllable.[66] 

The Camperdown program: This is a speech restructuring program that involves participants copying and adjusting their speech patterns to imitate a video exemplar.[67] 

The Van Riper method: This modification program substitutes maladaptive stuttering behaviors with preferred ones and consists of 4 stages—identification, desensitization, modification, and stabilization.

Additionally, transcranial direct current stimulation treatments have shown promising results in people who stutter.[68] In many cases, treatment modalities used to address developmental stuttering can also be applied to manage neurogenic stuttering.[36] A common approach involves speech therapy that integrates behavioral and cognitive measures.[69](A1)

In contrast to developmental stuttering, medications can be utilized to treat neurogenic stuttering.[69][70] These medications include haloperidol (the most common), chlorpromazine, trifluoperazine, thioridazine, carbamazepine, sodium valproate, levetiracetam, risperidone, and olanzapine. Although these drugs may offer assistance, they are not typically the initial treatment option, primarily due to their high incidence of adverse effects. Speech therapy remains the cornerstone of treatment.[36] 

Functional stuttering is typically diagnosed after excluding all organic causes of stuttering. As with other forms of stuttering, speech therapy serves as the primary treatment approach for functional stuttering, commencing after reassuring the patient that no underlying brain lesion is causing the condition. Successful treatment involves collaborative efforts between the speech-language therapist and the patient to develop a comprehensive understanding of the condition, incorporating all its diverse aspects. The patient can use the formulation to help explain to others the nature of their condition and its resolution. This explanation should highlight the patient's concerted efforts in managing the condition and regaining control.[30] Treatment for drug-induced stuttering involves discontinuing the causative agent or modifying its dosage or frequency of administration.[18]

Differential Diagnosis

Developmental stuttering should be distinguished from the "other disfluencies" that are considered normal during childhood. Clinicians can effectively differentiate between these various forms of stuttering through careful observation, evaluation, and a comprehensive history.

Distinguishing neurogenic stuttering from other communication disorders can pose significant challenges.[71][29] Substantial clinical overlap may occur with language conditions such as Tourette syndrome, palilalia, dysarthria, apraxia of speech, anomia, and aphasia.

In addition, distinguishing neurogenic stuttering from other neurological speech disorders can be challenging, as the boundaries between them are often blurred. A comprehensive understanding of stuttering disorders is essential to differentiate among and between the various forms of stuttering effectively.[12]

Prognosis

The prognosis of developmental stuttering is generally favorable in young children, with resolution rates ranging from 65% to 87%, irrespective of whether they received treatment.[22] However, as neural plasticity decreases with age, older individuals who continue to stutter generally have significantly lower rates of resolution.[6]

Psychogenic stuttering usually shows a rapid improvement in clinical symptoms soon after initiating therapy.[43] In contrast, neurogenic stuttering displays a slower, variable, and often less substantial treatment response.[12]

Complications

Individuals who stutter often develop amplified speech-motor preparation as a compensatory mechanism for their stuttering.[72] Stuttering involves a heightened level of conscious speech monitoring,[6] and stress can aggravate stuttering disfluencies.[73] In addition, the onset of stuttering can induce anxiety, which further impairs the ability to consciously monitor speech, which will in itself intensify the stuttering.[5] This creates a self-perpetuating, positive feedback loop of events, where anxiety worsens stuttering and vice versa.

Children who stutter may restrict their social interactions, which can hinder their social development and reduce their verbal output.[5] Additionally, adults who stutter are often negatively perceived by fluent speakers, who may view them as withdrawn, lacking confidence, and neurotic.[74][75] Data from the United States suggest that stuttering can adversely affect career and educational advancement.[76][77] For instance, one study revealed that stuttering had a detrimental impact on workplace performance and job satisfaction.[78]

Unfavorable reactions to stuttering can trigger anxiety, depression, and negative self-perception in individuals who stutter. Children who stutter may face bullying and teasing, exacerbating their challenges.[5] In addition, stuttering has been associated with a greater occurrence of suicidal ideation.[79]

In cases of acquired stuttering, it is essential to promptly identify the underlying etiology and tailor treatment protocols accordingly.