Vocal cord paralysis in myasthenia gravis with anti-MuSK antibodies

MuSK Myasthenia Gravis Presenting with Bilateral Vocal Cord Abduction Paresis: A Case Report and Literature Review

INTRODUCTION

Approximately 39% to 49% of patients with previously diagnosed acetylcholine receptor antibody-negative myasthenia gravis have been found to be muscle-specific tyrosine kinase (MuSK) antibody positive. These patients have a presentation that typically includes oculobulbar weakness, poorer response to cholinesterase inhibitors, and higher risk for acute clinical decompensation that necessitates plasma exchange. MuSK patients can require more aggressive maintenance immunosuppression earlier-on to maintain stability, often with rituximab.

CASE REPORT

The authors report the case of a 45-year-old woman who presented with months of worsening hoarseness and exertional dyspnea. Laryngoscopy revealed limited abduction of vocal cords bilaterally as the source of the complaint. Examination revealed ophthalmoparesis and fatigable proximal muscle weakness. She was found to have elevated MuSK antibodies that, along with evidence of neuromuscular junction transmission defect on nerve conduction studies, confirmed the diagnosis of MuSK myasthenia gravis. She experienced no improvement with pyridostigmine and decompensated despite receiving oral steroids, requiring intubation. However, she dramatically improved with plasma exchange and has since been doing well on rituximab therapy.

CONCLUSION

Dysphonia with hoarse quality secondary to vocal cord abduction paresis is a rare presentation of myasthenia gravis, as opposed to the typical flaccid dysarthria seen in bulbar myasthenia and should raise suspicion for MuSK antibody positivity. MuSK myasthenia gravis cases can be more refractory to treatment with cholinesterase inhibitors and are more likely to cause exacerbations and myasthenia crisis. Therefore, early and accurate diagnosis with appropriate antibody testing is imperative to avoid delays in treatment to prevent potentially life-threatening outcomes.

Bilateral vocal fold paresis: the only presenting sign of anti-MUSK antibody myasthenia gravis

A previously fit and well 53-year-old man was referred to the otolaryngology clinic with intermittent stridor and was found to have bilateral vocal fold paresis. Subsequent airway compromise necessitated emergency surgical tracheostomy. The man was discharged home with tracheostomy in situ and a diagnosis of idiopathic bilateral vocal cord palsy, as all primary investigations were negative. Neurological disease was suspected following readmission to hospital several weeks later with diplopia. Electromyography and serum antibody testing confirmed a diagnosis of anti-muscle-specific tyrosine kinase antibody positive myasthenia gravis (MuSK-MG); a subset of MG where autoantibodies are directed against MuSK. Resolution of bilateral vocal fold paresis was found 8 months after a short course of immunoglobulin (intravenous immunoglobulin (IVIg)) and daily mycophenolate therapy was commenced. Multidisciplinary teamwork between ear, nose and throat surgeons, neurologists and speech therapists enabled successful decannulation of tracheostomy. The patient has recovered well and remains minimally symptomatic.

Bilateral Vocal Fold Paralysis in Myasthenia Gravis: A Case Report and Literature Review

To prevent severe and potentially life-threatening consequences of bilateral vocal fold paralysis (BVFP), the identification and management of reversible causes is pivotal. Myasthenia gravis (MG) presenting with BVFP is rarely reported and remains incompletely understood. Although symptom control is achievable for most MG patients with sufficient therapy, atypical clinical presentation such as BVFP might preclude diagnosis and thus effective treatment. Here, we present a case of BVFP as leading manifestation of MG successfully treated with plasmapheresis. Moreover, we performed a literature review of the few existing cases reported between 1980 and 2020 indicating that elderly patients are particularly at risk for MG presenting with severe BVFP and that edrophonium testing with fiber optic endoscopic evaluation of swallowing (FEES) might be valuable for establishing the diagnosis. We conclude that clinicians should consider MG as possible and reversible cause for BVFP.

Pneumonia and hypercapnic respiratory failure

A 75-year-old woman was brought to the emergency department after she was found unconscious at her house. She had had a productive cough and fever up to 39°C for the previous 4 days. She had a past medical history of high blood pressure, paroxysmal atrial fibrillation and type 2 diabetes (without insulin therapy), and was regularly taking bisoprolol, propafenone, atorvastatin, metformin and aspirin. She was a nonsmoker and had no occupational exposures.

Can you diagnose this patient presenting with pneumonia and hypercapnic respiratory failure?http://bit.ly/2zz53zO

Muscle-Specific Tyrosine Kinase and Myasthenia Gravis Owing to Other Antibodies

Around 20% of patients with myasthenia gravis are acetylcholine receptor antibody negative; muscle-specific tyrosine kinase antibodies (MuSK) were identified as the cause of myasthenia gravis in 30% to 40% of these cases. Anti MuSK myasthenia gravis is associated with specific clinical phenotypes. One is a bulbar form with fewer ocular symptoms. Others show an isolated head drop or symptoms indistinguishable from acetylcholine receptor-positive myasthenia gravis. These patients usually respond well to immunosuppressive therapy, but not as well to cholinesterase inhibitors. Other antibodies associated with myasthenia gravis, including low-density lipoprotein receptor-related protein 4, are discussed.

Management challenges in muscle-specific tyrosine kinase myasthenia gravis

Myasthenia gravis with antibodies to muscle-specific tyrosine kinase (MuSK-MG) is generally considered a severe disease because of the associated weakness distribution with prevalent involvement of bulbar muscles and a rapidly progressive course and early respiratory crises. Its treatment can be unrewarding, owing to poor response to acetylcholinesterase inhibitors in most patients, disease relapses in spite of high-dose immunosuppression, and development of permanent bulbar weakness. High-dose prednisone plus plasma exchange is the recommended approach for treating rapidly progressive bulbar weakness. In the disease management, oral steroids proved effective, plasma exchange produced marked, albeit short-term, improvement, while conventional immunosuppressants were comparatively less effective. Rituximab is a promising treatment for refractory MuSK-MG; in uncontrolled studies, nearly all treated patients achieved significant improvement with substantial decrease of medication. It is yet to be clarified whether the early use of rituximab could prevent the permanent bulbar weakness, which constitutes a relevant disability in these patients.

Recommendations of the Neurolaryngology Study Group on laryngeal electromyography

The Neurolaryngology Study Group convened a multidisciplinary panel of experts in neuromuscular physiology, electromyography, physical medicine and rehabilitation, neurology, and laryngology to meet with interested members from the American Academy of Otolaryngology Head and Neck Surgery, the Neurolaryngology Subcommittee and the Neurolaryngology Study Group to address the use of laryngeal electromyography (LEMG) for electrodiagnosis of laryngeal disorders. The panel addressed the use of LEMG for: 1) diagnosis of vocal fold paresis, 2) best practice application of equipment and techniques for LEMG, 3) estimation of time of injury and prediction of recovery of neural injuries, 4) diagnosis of neuromuscular diseases of the laryngeal muscles, and, 5) differentiation between central nervous system and behaviorally based laryngeal disorders. The panel also addressed establishing standardized techniques and methods for future assessment of LEMG sensitivity, specificity and reliability for identification, assessment and prognosis of neurolaryngeal disorders. Previously an evidence-based review of the clinical utility of LEMG published in 2004 only found evidence supported that LEMG was possibly useful for guiding injections of botulinum toxin into the laryngeal muscles. An updated traditional/narrative literature review and expert opinions were used to direct discussion and format conclusions. In current clinical practice, LEMG is a qualitative and not a quantitative examination. Specific recommendations were made to standardize electrode types, muscles to be sampled, sampling techniques, and reporting requirements. Prospective studies are needed to determine the clinical utility of LEMG. Use of the standardized methods and reporting will support future studies correlating electro-diagnostic findings with voice and upper airway function.

Muscle-specific receptor tyrosine kinase antibody positive myasthenia gravis current status

Muscle-specific tyrosine-kinase-antibody-positive myasthenia gravis (MuSK-MG) has emerged as a distinct entity since 2001. This disease has been reported worldwide, but with varying rates among patients with generalized acetylcholine-receptor-antibody-negative MG. MuSK-MG was detected in approximately 37% of generalized acetylcholine receptor antibody-negative MG. MuSK-MG patients were predominantly female with more prominent facial and bulbar involvement and more frequent crises. Disease onset tended to be earlier. Patients tended to have a relatively poor edrophonium response but showed prominent decrement in the repetitive nerve stimulation test in the facial muscles. Patients were more likely to display poor tolerance of, or a lack of improvement with, anticholinesterase agents. Somewhat better response was observed with steroids and plasma exchange. Most were managed successfully with aggressive immunomodulatory therapies, although a higher proportion of MuSK-MG patients had a refractory course when compared with other forms of generalized MG. I present here an up-to-date overview on MuSK-MG based on our experience at the University of Alabama at Birmingham and the existing literature.