Dysphonia as a primary manifestation in myasthenia gravis (MG): a retrospective review of 7 cases among 1520 MG patients

Laryngeal Myasthenia Gravis in Voice Patients: Clinical, Serologic, and Neuromuscular Characterization of Seronegative Patients for Antibodies Against the Acetylcholine Receptor and Muscle-Specific Kinase

OBJECTIVE

Laryngeal myasthenia gravis (MG) is a focal manifestation of MG, and most patients are seronegative for antibodies against the acetylcholine receptor (AChR) and muscle-specific kinase (MuSK). The purpose of this study was to determine the incidence of anti-AChR and anti-Musk antibodies in voice patients and to characterize the clinical and neuromuscular profiles of these patients in order to guide the diagnosis of laryngeal MG.

STUDY DESIGN

This was a retrospective case-control study that included patients over the age of 18 who underwent laryngeal electromyography (LEMG) as part of their evaluation for neuromuscular junction dysfunction.

METHODS

Cases and controls were evaluated serologically, for the anti-AChR, anti-MuSK, and anti-striational muscle antibodies, and neuromuscularly using the Tensilon test in some patients, repetitive nerve stimulation (RNS) test, and a treatment trial of pyridostigmine bromide. Cases were defined as either (1) positive anti-AChR or anti-MuSK, or (2) a positive Tensilon test or positive pyridostigmine bromide trial.

RESULTS

Two hundred and eleven patients were screened; 61 (29%) patients were identified with laryngeal MG, and 77 (36%) patients were selected as controls. All case and control patients were seronegative for the anti-AChR and anti-MuSK antibodies with no significant difference between case and control status for seropositivity for anti-striational muscle antibodies. Of the case patients with an electrically positive Tensilon test (80.6%) who completed a treatment trial, 100% had symptom improvement. Of the case patients with a symptomatically positive Tensilon test (16.1%), only 60% of patients had improvement with a treatment trial. The RNS was more likely to be positive in case patients than control patients, and cases had a higher severity of paresis in all laryngeal muscles with LEMG evaluation.

CONCLUSIONS

Laryngeal MG is an underrecognized condition in the otolaryngology community owing in part to its seronegative presentation. Electrical improvement with a Tensilon test, or electrical or substantial symptomatic improvement with pyridostigmine bromide represents the most robust diagnostic criteria in these patients.

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.

Clinical features of laryngeal myasthenia gravis: A case series

BACKGROUND

Myasthenia gravis (MG) is an autoimmune disease. Dysarthria, dysphagia, and difficulty swallowing as exclusive initial and primary complaints in MG (laryngeal MG) are rare and seldom reported.

METHODS

Here we review and analyze the largest series of laryngeal MG patients.

RESULTS

A total of 30 patients with laryngeal MG as primary manifestation were found in 20 case reports/series. Dysarthria was the most frequent primary symptom (14/30), followed by dysphagia (11/30), slurred speech (4/30) and dysphonia (1/30). Sixty-three percent visited the otolaryngology department first. Only 23.33% of patients were diagnosed with MG at the first clinic visit. Forty-five percent laryngeal MG patients were acetylcholine receptor (AChR) antibody positive, 52.9% showed decremental response in the repetitive nerve stimulation (RNS) test, and 92.6% were positive in the neostigmine/edrophonium test. Fluctuating weakness was examined in 16 of 30 patients and observed in 14/16 patients.

CONCLUSION

Laryngeal MG is a rare and possibly under-diagnosed condition. The patients can present with dysarthria, dysphagia, or difficulty swallowing. Fluctuation in severity of disease by neostigmine/edrophonium test is a typical feature for MG patients. AChR antibody and RNS tests should be included to evaluate the pathologic changes in the neuromuscular junction.

Detectable voice change with the edrophonium test in laryngeal myasthenia gravis

A case of laryngeal myasthenia gravis in a 65-year-old woman presenting with hoarseness as the sole symptom is reported. Voice spectrography was performed before and after injection of intravenous edrophonium. There was a marked improvement in the patient's voice after the administration of edrophonium, which was confirmed by the changes seen on the sound spectrogram. This was the only objective indication of a diagnosis of myasthenia gravis. No thymoma was seen on chest X-ray and the patient was negative for anti-acetylcholine receptor antibodies. Treatment for laryngeal myasthenia gravis was initiated and the patient's vocal problems resolved. This case emphasizes the need to consider systemic diseases in the differential diagnosis of hoarseness and demonstrates the need for careful follow-up in such patients.

Disfonia como principal queixa num quadro de miastenia grave: diagnóstico e fonoterapia

Miastenia grave é uma doença autoimune que se manifesta por fraqueza e fadiga muscular progressivas. São frequentes os sintomas oculares e bulbares, dentre eles, a disfonia. Este artigo relata um caso de disfonia, cuja avaliação fonoaudiológica contribuiu com o diagnóstico de miastenia grave e seu tratamento. A paciente em questão procurou o atendimento fonoaudiológico com diagnóstico otorrinolaringológico de presbifonia. A avaliação perceptivo-auditiva e acústica da voz identificou alterações em respiração, fonte glótica e filtro/ressonância. Como alguns dados obtidos com a anamnese e observados nas provas vocais não se relacionavam diretamente com a presença de presbifonia, houve a necessidade de discussão do caso com o médico, quando ambos concluíram a necessidade de encaminhar a paciente para avaliação neurológica. O neurologista consultado levantou a hipótese diagnóstica de miastenia grave e solicitou exames. A paciente seguiu em acompanhamento fonoaudiológico e medicamentoso. Na reavaliação vocal, ocorrida cerca de dois meses após o início do tratamento, foi constatada melhora na qualidade vocal, com grande impacto na qualidade de vida. Este trabalho evidencia a importância da avaliação fonoaudiológica detalhada e da participação do fonoaudiólogo na equipe interdisciplinar.

Clinical and electrophysiological characteristics of larynx in myasthenia gravis

OBJECTIVES

We investigated the clinical and electrophysiological characteristics of the larynx in patients with myasthenia gravis (MG).

METHODS

Thirty-two cases of MG were analyzed. The laryngeal behaviors and characteristics of laryngeal electromyography were evaluated, and voice assessment and repetitive nerve stimulation (RNS) tests were conducted.

RESULTS

The initial symptoms of patients were ptosis and/or diplopia in 28, dysphagia and slurred speech in 3, and limb weakness in 1. Only 8 patients had slight hoarseness and vocal fatigue, and 4 patients had positive laryngeal signs. When compared with normal subjects, the patients with MG had worse results on the acoustic analysis of shimmer, their normalized noise energy was greater, and the harmonics-to-noise ratio and maximum phonation time were significantly lower. The RNS findings were positive in 28 patients and negative in 4 patients. The average (+/-SD) amplitude decrement was 31.9% +/- 19.1%. The mean number of involved laryngeal muscles was 2.22 +/- 1.35. Cricothyroid muscles were involved in 26 cases, thyroarytenoid muscles were involved in 14 cases, posterior cricoarytenoid muscles were involved in 6 cases, and lateral cricoarytenoid muscles were involved in 2 cases.

CONCLUSIONS

Although few patients presented with laryngeal symptoms as their initial symptoms, most patients with MG exhibited asymmetry and abnormal findings on laryngeal electromyography. The RNS test for laryngeal muscles is a more sensitive indicator for the diagnosis of MG, especially in the cricothyroid muscle.

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.