Juvenile seropositive myasthenia gravis with anti-MuSK antibody after thymectomy

A very late onset AChR and MuSK double positive myasthenia gravis: a case description and literature review

AChR and MuSK double positive myasthenia gravis has been rarely reported. Generally, it occurs in children and adults after thymectomy or immunotherapy. Furthermore, in a few patients with bulbar or respiratory involvement, MuSK antibodies might be detected after clinical deterioration. We report a man with a very late onset myasthenia gravis (86-year-old) and the coexistence of both antibodies at the time of the diagnosis. Despite the presence of MuSK antibodies, he manifested no bulbar symptoms and had a favorable clinical outcome. However, side effects related to low dose pyridostigmine were evident. Hence, double positivity can also occur in elderly and in more benign forms of myasthenia gravis. Other cases of AChR and MuSK double positive myasthenia gravis could allow a better definition of this condition.

Juvenile Generalized Myasthenia Gravis With AChR and MuSK Antibody Double Positivity: A Case Report With a Review of the Literature

Myasthenia gravis is an autoimmune disease mediated by B cells and is associated with acetylcholine receptor (AChR) and muscle-specific receptor tyrosine kinase (MuSK) antibodies in the postsynaptic membrane at the neuromuscular junction. The presence of both antibodies in the serum of patients with myasthenia gravis has been rarely reported. Case description: A 9-year-old girl was admitted to our hospital with the chief complaints of reduced facial expression for 3 months and unclear speech and choking from drinking water for 2 months. The diagnosis of generalized myasthenia gravis was made based on clinical manifestations, repetitive electrical nerve stimulation, neostigmine tests, specific antibody tests and other auxiliary examinations. We found the rare coexistence of two key antibodies (anti-AChR and anti-MuSK antibodies) in the patient's serum. The patient experienced myasthenic crisis and received respiratory support even though she was taking prednisone therapy. Due to the poor response to treatment with pyridostigmine bromide, glucocorticoids and IVIG, we administered rituximab therapy, and she responded well and achieved clinical remission. This suggests that clinicians should pay more attention to atypical cases and antibody detection. Rituximab should be considered when conventional treatment fails.

Effectiveness of thymectomy in juvenile myasthenia gravis and clinical characteristics associated with better outcomes

Thymectomy is an established treatment in adult myasthenia gravis, but its exact role in juvenile myasthenia gravis (JMG) is still uncertain. Thymectomy is frequently considered in the treatment of severe, medically refractory JMG. Surgical approaches have evolved from open median sternotomy to the more cosmesis-preserving thoracoscopic approach. This paper reviews current evidence on the effectiveness of thymectomy in JMG and discusses clinical characteristics which may be associated with improved outcomes. 17 studies including 588 patients who underwent thymectomy from 1997 to 2020 were found, which either reported uncontrolled cohorts undergoing thymectomy, or compared cohorts undergoing different surgical approaches. An improvement in clinical status or reduced requirement for medical therapy following thymectomy was seen in 453 patients (77%). Complete remission was seen in 40% (n = 172/430). Thoracoscopic approaches may provide improved outcomes, fewer complications, and better cosmetic outcomes. Better surgical outcomes may be associated with early intervention, intervention after the onset of puberty, being acetylcholine receptor antibody positive, having more severe disease and the presence of hyperplastic thymic tissue. However, analysis remains hindered by the limitations of the currently available retrospective studies of small cohorts. Nonetheless, available literature suggests a role for thymectomy in JMG patients, especially those with certain clinical characteristics.

AChRAb and MuSKAb double-seropositive myasthenia gravis: a distinct subtype?

Introduction

This study investigated the characteristics of double-seropositive myasthenia gravis (DSP-MG) in southern China for disease subtype classification.

Methods

A case-control study was carried out in which the characteristics of DSP-MG patients (n = 17) were compared to those of muscle-specific tyrosine kinase antibody-positive (MuSK)-MG and acetylcholine receptor antibody-positive (AChR)-MG patients (n = 8 and 27, respectively). We also performed a literature review of DSP-MG patients.

Results

Compared to AChR-MG, DSP-MG had greater bulbar dysfunction (47.1% vs 18.6%, P = 0.04), higher incidence of myasthenia crisis (41.2% vs 14.8%, P = 0.04), more severe Myasthenia Gravis Foundation of America classification at maximum worsening, greater autoantibody abnormalities (70.6% vs 33.3%, P = 0.015), greater need for immunosuppressant treatment (58.8% vs 3.7%, P < 0.001), and worse prognosis with less remission (11.8% vs 55.6%, P = 0.001). There were no differences between DSP-MG and MuSK-MG patients. DSP-MG described in published reports was comparable to MuSK-MG.

Discussion

DSP-MG in southern China may be a subtype of MuSK-MG.

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.

Myasthenic Crisis Complicated with Myxedema, Positive for Both Anti-acetylcholine Receptor and Anti-muscle-specific Tyrosine Kinase Antibodies

We herein report the case of myasthenic crisis occurring in a 51-year-old man. He had experienced ptosis, increased body weight with edema, and fatigue with dyspnea. He presented at our emergency department with disturbed consciousness. He was originally diagnosed with myxedema coma, and he required artificial respiration. Because his weakness persisted and he was positive for anti-acetylcholine receptor antibodies and anti-muscle-specific tyrosine kinase antibodies, we diagnosed myasthenic crisis after various examinations. His clinical response to treatment was good and he was discharged in an ambulatory status 3 months after admission. This case demonstrates that myasthenic crisis may occur in association with myxedema.

Complicating autoimmune diseases in myasthenia gravis: a review

Myasthenia gravis (MG) is a rare autoimmune disease of skeletal muscle endplates. MG subgroup is relevant for comorbidity, but usually not accounted for. MG patients have an increased risk for complicating autoimmune diseases, most commonly autoimmune thyroid disease, systemic lupus erythematosus and rheumatoid arthritis. In this review, we present concomitant autoimmune disorders associated with the different MG subgroups, and show how this influences treatment and prognosis. Concomitant MG should always be considered in patients with an autoimmune disorder and developing new neuromuscular weakness, fatigue or respiratory failure. When a second autoimmune disorder is suspected, MG should be included as a differential diagnosis.

Early-onset acquired myasthenia gravis secondary to anti-muscle-specific kinase autoantibodies

Autoimmune myasthenia gravis is rarely seen during infancy. Similar to adults, 85% to 90% of generalized pediatric myasthenia gravis cases have acetylcholine receptor antibodies. Approximately 30% of the remaining cases have antibodies against muscle-specific kinase. Information on the clinical course, treatment alternatives, and prognosis of pediatric muscle-specific kinase antibody-positive myasthenia gravis is limited because of the small number of cases. Here, we present a 14-month-old girl with muscle-specific kinase antibody-positive myasthenia gravis as one of the youngest patients described so far in the literature.

Diagnosis and therapy of myasthenia gravis with antibodies to muscle-specific kinase

Myasthenia gravis (MG) with antibodies to the muscle-specific receptor tyrosine kinase (MuSK-MG) is a rare disease which covers 5-8% of all MG patients. Symptoms are nearly always generalized, though more focal than in MG with anti-acetylcholine receptor antibodies, with predominant involvement of cranial, bulbar and axial muscles; early respiratory crises are frequent. Focal atrophy, mostly of facial, masseter and tongue muscles, occurs in a proportion of patients. Diagnosis is often challenging on account of atypical presentation with little or no symptom fluctuations, lack of response to acetylcholinesterase inhibitors in a high proportion of patients and negative results of electrodiagnostic studies when performed on limb muscles. Immunosuppression is the mainstay of treatment, since the response to acetylcholinesterase inhibitors is generally unsatisfactory and thymectomy does not appear to improve the course of the disease. Although corticosteroids result in marked improvement, disease flares are frequent during prednisone dosage tapering and most patients remain dependent on treatment. Since treatment with rituximab, in uncontrolled studies, induced sustained benefit in patients with refractory disease, B cell depletion is an attractive option for MuSK-MG patients unresponsive to conventional immunosuppressants.

Juvenile myasthenia gravis: a paediatric perspective

Myasthenia gravis (MG) is an autoimmune disease in which antibodies are directed against the postsynaptic membrane of the neuromuscular junction, resulting in muscle weakness and fatigability. Juvenile myasthenia gravis (JMG) is a rare condition of childhood and has many clinical features that are distinct from adult MG. Prepubertal children in particular have a higher prevalence of isolated ocular symptoms, lower frequency of acetylcholine receptor antibodies, and a higher probability of achieving remission. Diagnosis in young children can be complicated by the need to differentiate from congenital myasthenic syndromes, which do not have an autoimmune basis. Treatment commonly includes anticholinesterases, corticosteroids with or without steroid-sparing agents, and newer immune modulating agents. Plasma exchange and intravenous immunoglobulin (IVIG) are effective in preparation for surgery and in treatment of myasthenic crisis. Thymectomy increases remission rates. Diagnosis and management of children with JMG should take account of their developmental needs, natural history of the condition, and side-effect profiles of treatment options.

Acquired myasthenia gravis in childhood

PURPOSE OF REVIEW

This review discusses recent studies on myasthenia gravis with onset in childhood (juvenile myasthenia gravis) and neonatal myasthenia gravis.

RECENT FINDINGS

The occurrence of myasthenia gravis in childhood is strongly influenced by genetic and environmental factors. Juvenile myasthenia gravis is associated with antibodies to the acetylcholine receptor (AChR) in most patients. Thymoma is rare, but often malignant in children. The frequency of juvenile myasthenia gravis with antibodies to the muscle-specific kinase (MuSK) varies markedly in different countries; some distinct features have been described. Management of juvenile myasthenia gravis does not differ, on the whole, from that of adult myasthenia gravis. Timing of thymectomy in young children is still controversial. Maternal antifetal type AChR antibodies can cause persistent focal weakness in the offspring, while neonatal myasthenia gravis associated with MuSK antibodies is often a severe and protracted albeit transient disease.

SUMMARY

Juvenile myasthenia gravis, like its adult-onset counterpart, is a heterogeneous disease. Clinical presentation is influenced by antibody status, ethnicity and age of onset. Treatment is very effective, but guidelines and controlled trials are needed.The risk for neonatal myasthenia gravis appears to be markedly influenced by maternal antibody subclass and antigen specificity. Adequate treatment in mothers can reduce both frequency and severity of neonatal disease.