Introduction

Nemaline myopathy (NM) is a congenital neuromuscular disorder characterised by muscle weakness and the presence of nemaline rods (thread-like structures) in muscle fibres on histological examination. It is clinically heterogeneous, with varying ages of onset, severity, and muscle group involvement.^1,2 A significant feature of many NM subtypes is the involvement of facial and bulbar muscles, which may lead to dysarthria (speech difficulties) and dysphagia (swallowing difficulties). These manifestations considerably impact the quality of life and often require multidisciplinary management strategies.^1,2 This article explores the pathophysiological mechanisms, clinical features, diagnostic approaches, and management of speech and swallowing difficulties resulting from facial and bulbar muscle involvement in nemaline myopathy.

Overview of nemaline myopathy

Nemaline myopathy is classified within the congenital myopathies and is caused by mutations in various genes encoding sarcomeric proteins, including ACTA1, NEB, TPM2, TPM3, TNNT1, and CFL2.¹ These mutations disrupt thin filament assembly and function, leading to structural abnormalities and muscle weakness. The hallmark histological feature is the presence of nemaline bodies within muscle fibres, visualised using Gomori trichrome stain.²

The disease presents in different clinical forms: severe congenital, intermediate congenital, typical congenital, childhood-onset, and adult-onset forms. Facial and bulbar weakness is especially prominent in the more severe forms, but can also appear in intermediate and milder types.³

Facial muscle involvement

Facial weakness is a characteristic and often early feature of NM. Patients typically present with hypotonic facies, an open mouth posture, a tented upper lip (myopathic facies), and poor facial expression.⁴ These manifestations arise due to weakness of the orbicularis oris, zygomaticus major( muscle for facial expression, including smiling), and other mimetic muscles.

This muscle involvement can affect both verbal and nonverbal communication. Children may show delayed acquisition of facial gestures and smiling, and adults may experience reduced facial expressiveness. Drooping facial muscles can result in drooling and poor oral competence, further complicating feeding and articulation.⁵

Importantly, facial muscle weakness not only impacts aesthetics and social interactions but also affects functional tasks such as blowing, sucking, and phonation. The inability to seal the lips tightly can cause air leakage during speech and food spillage during eating, compounding bulbar dysfunction. 

Bulbar muscle involvement and dysphagia

Bulbar muscles, including the tongue, pharyngeal constrictors, and soft palate, are critical for swallowing and speech. In NM, these muscles may be affected to varying degrees, especially in early-onset and congenital forms. The weakness of the tongue and pharyngeal muscles contributes to dysphagia, which may manifest as poor suckling in neonates, prolonged feeding time, nasal regurgitation, and aspiration.⁷

Dysphagia in NM has a neuromuscular origin; weakness in the oropharyngeal musculature leads to poor bolus formation and propulsion. Hypotonia of the palatal muscles may result in hypernasal speech and nasal regurgitation of liquids.⁸ Laryngeal muscle weakness may further compromise airway protection, increasing the risk of aspiration pneumonia.

Feeding difficulties are so prominent in some cases that gastrostomy tube placement is required early in life.⁹ Even in milder cases, feeding may remain inefficient, requiring nutritional support, thickened fluids, or compensatory swallowing techniques.

Dysarthria and speech impairment

Speech difficulties in NM primarily result from dysarthria, a motor speech disorder caused by the impairment of the muscles involved in speech production. Dysarthria in NM is typically flaccid due to lower motor neuron or muscular involvement, leading to reduced strength, tone, and movement precision in articulators.¹⁰

Common features include: Imprecise consonant articulation, Hypernasality, Reduced speech intelligibility, Slow speaking rate, and Monotone voice quality.¹¹ These characteristics are compounded by facial weakness, palatal insufficiency, and respiratory muscle involvement, which influence phonation, resonance, and articulation.

Speech development in children with NM may be delayed, particularly when early facial and bulbar weakness is significant. In some cases, augmentative and alternative communication (AAC) tools may be introduced to support language development.¹²

Pathophysiology of bulbar weakness in NM

The underlying pathophysiology of bulbar involvement in NM lies in the mutation-driven impairment of sarcomeric proteins. These proteins are integral to muscle contraction, and their dysfunction leads to selective vulnerability of certain muscle groups, particularly cranial nerve–innervated muscles.¹³

The tongue and pharyngeal muscles, with their unique fibre-type composition and high activity during eating and speaking, are often early and prominently affected. The nemaline rods accumulate within these muscle fibres, disrupting normal contractility and leading to progressive atrophy and weakness.¹⁴

Electrophysiological studies may show reduced compound muscle action potentials (CMAPs), while a muscle biopsy confirms the diagnosis. In NM, involvement is typically non-progressive or slowly progressive, but bulbar symptoms may fluctuate or worsen with intercurrent illness or fatigue.¹⁵

Diagnostic considerations

The diagnosis of NM requires a combination of clinical evaluation, muscle biopsy, genetic testing, and neurophysiological studies. Assessment of bulbar and facial muscle function is crucial in patients with suspected NM. This includes: Oral motor examination, Video fluoroscopic swallow study (VFSS), Fiberoptic endoscopic evaluation of swallowing (FEES), and Speech and language evaluation. ^[16] Muscle biopsy remains important for visualising nemaline bodies. However, next-generation sequencing panels have facilitated earlier and more precise diagnosis through genetic confirmation. Early involvement of a multidisciplinary team—neurologists, speech-language pathologists (SLPs), dietitians, and geneticists—is essential for comprehensive care.¹⁷

Management Strategies: Management of facial and bulbar weakness in NM is largely supportive and focuses on optimising feeding, communication, and respiratory safety.

Speech and Language Therapy: SLPs play a central role in assessing and managing dysarthria and dysphagia. Interventions may include: oral motor exercises (though their efficacy is variable), compensatory speech strategies, Palatal lift prostheses for velopharyngeal incompetence, and AAC systems in severe cases.¹⁸ Early initiation of therapy can enhance speech intelligibility and prevent social withdrawal due to communication difficulties.

Swallowing and Feeding Interventions: Feeding strategies include: Positioning adjustments during feeding, thickened fluids to prevent aspiration, modified textures (e.g., pureed foods), adaptive utensils for self-feeding, and enteral feeding (e.g., nasogastric or gastrostomy tubes) when oral feeding is unsafe.¹⁹ Ongoing monitoring is critical, as dysphagia can worsen with growth or intercurrent respiratory infections.

 Surgical and Dental Support: Orthodontic evaluation may be required for children with persistent open-mouth posture or malocclusion due to facial hypotonia. Dental care is important due to the risk of food pooling and aspiration.²⁰

Prognosis and Quality of Life: The long-term outcome for individuals with NM varies widely depending on the severity and specific genetic subtype. In cases with prominent facial and bulbar involvement, early and continuous supportive interventions can significantly improve nutritional status, prevent aspiration, and enhance communication. Despite their physical limitations, many individuals with NM lead productive lives, particularly when provided with early multidisciplinary support. Quality of life is closely linked to functional speech and safe swallowing, highlighting the importance of addressing these features proactively.²¹

Conclusion

Facial and bulbar muscle involvement in nemaline myopathy presents significant challenges, especially in terms of speech and swallowing. These manifestations can be life-limiting and socially isolating without appropriate support. Multidisciplinary care, early diagnosis, and individualised interventions remain the cornerstone of management. While curative therapies are still under investigation, supportive strategies offer meaningful improvements in daily functioning and quality of life for affected individuals.