Seronegative myasthenia gravis: clinical features, response to therapy and synthesis of acetylcholine receptor antibodies in vitro

Analysis of clinical features and outcomes in patients with ocular myasthenia gravis according to anti-acetylcholine receptor antibody-seropositivity

PURPOSE

To comparatively analyze the clinical characteristics of patients with ocular myasthenia gravis (OMG) referred to an ophthalmology clinic, according to anti-acetylcholine receptor antibody (AchR Ab)-seropositivity.

STUDY DESIGN

Retrospective Cohort Study.

METHODS

Medical records of patients with OMG who presented to a tertiary eye care center between 2003 and 2020 were retrospectively reviewed. Demographics, ophthalmologic characteristics, response to medical treatment, presence of autoimmune thyroid disease and thyroid autoantibody were compared between the AchR Ab seropositive and seronegative groups.

RESULTS

A total of 130 patients with OMG were identified; among them, 46 patients (35.4%) had autoantibody against acetylcholine receptors. The mean age at symptom onset was 42.4 ± 18.9 years. There were no differences in mean age at symptom onset, gender ratio, and mean follow-up period between patients with seropositive and seronegative OMG. Graves ophthalmopathy was significantly more frequent in seronegative patients (p = 0.04), while thymic disease (p < 0.01) was more frequent in seropositive patients (p < 0.01). Among patients with seropositive OMG, 52.3% showed a good response to medical treatment, while only 31.4% of the seronegative patients were classified as good responders (p = 0.01). Thyroid dysfunction was found in 27.4% patients with OMG and the proportion of thyroid dysfunction was not different according to anti-acetylcholine receptor antibody-seropositivity.

CONCLUSION

Seropositivity to acetylcholine receptor antibody is associated with a better response to medical treatment and lower risk of concomitant autoimmune thyroid disease in patients with OMG.

Novel Treatments in Myasthenia Gravis

Myasthenia gravis (MG) is the prototypical autoimmune disorder caused by specific autoantibodies at the neuromuscular junction. Broad-based immunotherapies, such as corticosteroids, azathioprine, mycophenolate, tacrolimus, and cyclosporine, have been effective in controlling symptoms of myasthenia. While being effective in a majority of MG patients many of these immunosuppressive agents are associated with long-term side effects, often intolerable for patients, and take several months to be effective. With advances in translational research and drug development capabilities, more directed therapeutic agents that can alter the future of MG treatment have been developed. This review focuses on the aberrant immunological processes in MG, the novel agents that target them along with the clinical evidence for efficacy and safety. These agents include terminal complement C5 inhibitors, Fc receptor inhibitors, B cell depleting agents (anti CD 19 and 20 and B cell activating factor [BAFF)]inhibitors), proteosome inhibitors, T cells and cytokine based therapies (chimeric antigen receptor T [CART-T] cell therapy), autologous stem cell transplantation, and subcutaneous immunoglobulin (SCIG). Most of these new agents have advantages over conventional immunosuppressive treatment (IST) for MG therapy in terms of faster onset of action, favourable side effect profile and the potential for a sustained and long-term remission.

Clinical features of LRP4/agrin-antibody-positive myasthenia gravis: A multicenter study

Introduction

Our aim in this study was to identify the prevalence and clinical characteristics of LRP4/agrin‐antibody–positive double‐seronegative myasthenia gravis (DNMG).

Methods

DNMG patients at 16 sites in the United States were tested for LRP4 and agrin antibodies, and the clinical data were collected.

Results

Of 181 DNMG patients, 27 (14.9%) were positive for either low‐density lipoprotein receptor–related protein 4 (LRP4) or agrin antibodies. Twenty‐three DNMG patients (12.7%) were positive for both antibodies. More antibody‐positive patients presented with generalized symptoms (69%) compared with antibody‐negative patients (43%) (P ≤ .02). Antibody‐positive patients’ maximum classification on the Myasthenia Gravis Foundation of America (MGFA) scale was significantly higher than that for antibody‐negative patients (P ≤ .005). Seventy percent of antibody‐positive patients were classified as MGFA class III, IV, or V compared with 39% of antibody‐negative patients. Most LRP4‐ and agrin‐antibody–positive patients (24 of 27, 89%) developed generalized myathenia gravis (MG), but with standard MG treatment 81.5% (22 of 27) improved to MGFA class I or II during a mean follow‐up of 11 years.

Discussion

Antibody‐positive patients had more severe clinical disease than antibody‐negative patients. Most DNMG patients responded to standard therapy regardless of antibody status.

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.

Serological and clinical features of patients with myasthenia gravis in north Indian population

Myasthenia gravis (MG) is a disorder of neuromuscular junction associated with presence of antibodies against nicotinic acetylcholine receptors (nAChRs). Here, we compared the clinical and serological profile of seropositive myasthenia gravis (SPMG) and seronegative myasthenia gravis (SNMG) patients. Anti-AChR antibody was measured using radio receptor immunoassay and correlated with clinical phenotype in 250 MG patients over 2004 and 2006. Out of 250 MG patients, 161 (64.4%) were males (male:female = 1.8:1). SNMG patients formed 40% (n = 101) of our MG patients which is much higher as compared to Caucasian and Oriental population (15%-20%). The median age of disease onset in SPMG was significantly higher than SNMG patients (43 years; range 8-74 vs. 35 years; range 4-72, p = .022). A bimodal peak of age of disease onset in both genders was observed (first peak in second-third decades and second one in fifth-sixth decades). Among the MG patients with late-onset of disease, male were significantly higher compared to Caucasian and Oriental MG population (p = .047). MG patients with thymoma were significantly older and consisted of higher percent of males. Bulbar symptoms and severe grade (IIB+ III+ IV) at disease onset were more frequent in SPMG than SNMG patients.

[Seronegative myasthenia gravis]

Six to 20 p.cent of patients with generalized myasthenia gravis and 30 to 50 p.cent of those with ocular myasthenia gravis do not have anti AchR antibodies. Strict clinical, pharmacological and electrophysiological criteria are needed for the diagnosis of sero-negative myasthenia gravis. Sero-negative myasthenia gravis is an autoimmune disorder. But thymic hyperplasia is generally absent. Antibodies directed against the muscle receptor of tyrosine kinase (anti MuSK antibodies) were recently demonstrated in 40 to 70 p.cent of patients with sero-negative myasthenia gravis. Sero-negative and sero-positive myasthenia gravis may be clinically very similar. But sero-negative myasthenia gravis may express predominantly severe oculobulbar weakness or mainly neck, shoulder and respiratory muscle weakness. Sero-negative myasthenia gravis is never associated with thymoma. Sero-negative myasthenia gravis responds to immunodulation but perhaps less well than sero-positive myasthenia gravis.

Detection and characterization of MuSK antibodies in seronegative myasthenia gravis

Antibodies to rat muscle specific kinase, MuSK, have recently been identified in some generalized "seronegative" myasthenia gravis (SNMG) patients, who are often females with marked bulbar symptoms. Using immunoprecipitation of (125)I-labelled-human MuSK, 27 of 66 (41%) seronegative patients were positive, but 18 ocular SNMG patients, 105 AChR antibody positive MG patients, and 108 controls were negative. The antibodies are of high affinity (Kds around 100 pM) with titers between 1 and 200 nM. They bind to the extracellular Ig-like domains of soluble or native MuSK. Surprisingly they are predominantly in the IgG4 subclass. MuSK-antibody associated MG may be different in etiological and pathological mechanisms.

Seronegative generalised myasthenia gravis: clinical features, antibodies, and their targets

Myasthenia gravis (MG) is a well-recognised disorder of neuromuscular transmission that can be diagnosed by the presence of antibodies to the acetylcholine receptor (AChR). However, some patients (about 15%) with generalised MG do not have detectable AChR antibodies. There is some evidence, however, that this "seronegative" MG is an antibody-mediated disorder. Plasma from patients with the disorder seems to contain various distinct humoral factors: IgG antibodies that reversibly inhibit AChR function; a non-IgG (possibly IgM) factor that indirectly inhibits AChR function; and an IgG antibody against the muscle-specific kinase (MuSK). The presence of antibodies against MuSK appears to define a subgroup of patients with seronegative MG who have predominantly localised, in many cases bulbar, muscle weaknesses (face, tongue, pharynx, etc) and reduced response to conventional immunosuppressive treatments. Moreover, muscle wasting may be present, which prevents complete response to these therapies.

Laryngeal Myasthenia Gravis: Report of 40 Cases

Myasthenia gravis, an autoimmune disorder of the neuromuscular junction, is usually recognized because of ocular complaints or generalized weakness. We report a series of 40 patients who presented with dysphonia as their initial and primary complaint. Diagnostic testing included strobovideolaryngoscopy, electromyography (EMG) with repetitive stimulation and Tensilon testing, and laboratory and radiographic evaluation. Strobovideolaryngoscopy most commonly revealed fluctuating impairment of vocal fold mobility, either unilateral or bilateral. EMG detected evidence of neuromuscular junction abnormalities in all patients. Only one patient had evidence of antiacetylcholine receptor (ACh-R) antibodies, but many other abnormalities suggestive of autoimmune dysfunction were present. Pyridostigmine therapy was initiated in 34 patients but was not tolerated in 4. Of the remaining 30 patients, 23 reported improvement of symptoms. We conclude that myasthenia gravis can present with symptoms confined primarily to the larynx and should be included in the differential diagnosis of dysphonia.

Seronegative myasthenia gravis and human immunodeficiency virus infection: response to intravenous gamma globulin and prednisone

BACKGROUND

There are only rare reports of myasthenia gravis complicating human immunodeficiency virus infection. The role of immunomodulatory therapy is unknown.

METHODS

Case report and literature review.

RESULTS

The diagnosis of human immunodeficiency virus infection followed that of myasthenia gravis in a 35-year-old man. Clinical and electrophysiological features were diagnostic of generalized myasthenia gravis but two edrophonium chloride tests and acetylcholine receptor antibodies were negative. Prednisone therapy and intravenous gamma globulin were associated with rapid clinical recovery.

CONCLUSIONS

Prednisone therapy and intravenous gamma globulin may be helpful in patients with generalized myasthenia gravis complicating HIV infection.

Exacerbation of myasthenia gravis during the menstrual period

BACKGROUND

Myasthenia gravis (MG) is an autoimmune disorder mediated by antiacetylcholine receptor antibodies. It has long been suspected to exacerbate during the menstrual period but this has never been adequately documented.

SUBJECTS AND METHODS

We questioned 120 female myasthenic patients of different ages, about their myasthenic symptoms before and during the menstrual period. We also evaluated the effect of medications, pain and stress during or before the menstrual period on the exacerbation rate. Exclusion criteria were postmenopausal age and incomplete information available in the questionnaire.

RESULTS

Forty two premenopausal women with generalized disease were included in the study. Twenty eight (67%) of the patients reported exacerbation of their myasthenic symptoms 2 to 3 days prior to the menstrual period. This exacerbation persisted in 22 of them to the third day of the menstrual period. In nine of the women this clinical worsening necessitated an increased intake of medications during the days prior to menstruation. No correlation could be found between the presence of antiacetylcholine receptor antibodies, pain, stress, use of oral contraceptives or the type of antimyasthenic therapy and the rate of exacerbation before and during the menstrual period.

CONCLUSIONS

(1) MG frequently exacerbates before and during the menstrual period in 67% of MG patients. (2) The rate of exacerbation is unrelated to the presence of stress or pain prior to or during the menstrual period. (3) Different therapies directed against MG, as well as oral contraceptives do not influence the clinical course. (4) Menstrual exacerbations occur in both seronegative and seropositive patients. (5) These exacerbations may frequently necessitate therapeutic changes.

Clinical heterogeneity of seronegative myasthenia gravis

We studied 38 patients affected by seronegative myasthenia gravis (SNMG) with age at the onset of the disease ranging from 6 to 66 yr. Clinical follow-up lasted at least 2 yr. Patients' lymphocyte cultures showed in no case anti-acetylcholine receptor antibody production; HLA associations did not differ significantly from those in seropositive MG. In most cases (33 out of 38) the disease differed from seropositive MG only in the low incidence of thymic pathology. In five cases the clinical picture was characterized by prevalent involvement of ocular and bulbar muscles and by a more stable course. These last group of patients did not respond satisfactorily to immunosuppressants, but they clearly improved with plasma-exchange. Mice injected with plasma IgG from four patients (two with typical clinical picture and two with prevalent oculobulbar involvement) showed a defect of neuromuscular transmission. In our experience, SNMG is a heterogeneous disease. A humorally mediated pathogenesis appears to be operating in both groups of patients we described.

Myasthenia gravis in the elderly: a hospital based study

To evaluate clinical characteristics and outcome of myasthenia gravis (MG) in aged patients (> 60yrs), we retrospectively reviewed a continuous series of 122 myasthenic patients observed from January 1968 through December 1994. Patients with congenital, neonatal, or penicillamine-induced myasthenia were excluded. Twenty-five subjects (20%) were > 60yrs. The male/female ratio was 3:2; 20% of patients had an ocular form and 86% were seropositive. Mediastinum CT scan revealed thymic changes in 14%. During the first five years of disease, 60% of patients with ocular form progressed towards a generalized form and 15% had clinical relapses. At the time of their last visit, 40% of patients were asymptomatic and 60% had improved on medication. No patient died because of myasthenia-related causes. This study shows that MG in aged patients is characterized by prevalence in males, low frequency of ocular forms, low frequency of positive mediastinum CT which suggests low frequency of thymomas, high frequency of progression of ocular forms, and good response to corticosteroid therapy.

Ocular myasthenia: a protean disorder

Ocular myasthenia is a localized form of myasthenia clinically involving only the extraocular, levator palpebrae superioris, and/or orbicularis oculi muscles. Ocular manifestations can masquerade as a variety of ocular motility disorders, including cranial nerve and gaze palsies. A history of variable and fatiguable muscle weakness suggests this diagnosis, which may be confirmed by the edrophonium (Tensilon) test and acetylcholine receptor antibody titer. Anticholinesterases, corticosteroids and other immunosuppressive agents, and other therapeutic modalities, including thymectomy and plasmapheresis, are used in treatment. As the pathophysiology of myasthenia has been elucidated in recent years, newer treatment strategies have evolved, resulting in a much more favorable prognosis than several decades ago. This review provides historical background, pathophysiology, immuno-genetics, diagnostic testing, and treatment options for ocular myasthenia, as well as a discussion of drug-induced myasthenic syndromes.

Antibody-secreting cells to acetylcholine receptor and to presynaptic membrane receptor in seronegative myasthenia gravis

Peripheral blood and bone marrow from seronegative and seropositive myasthenics were evaluated for antibody-secreting cells (ASC). Cells secreting antibody to acetylcholine receptor (AchR) and to presynaptic membrane receptor (prsmR) were counted using an immunospot assay. Immunoglobulin G (IgG) anti-AchR ASC were present in peripheral blood lymphocytes (PBL) from nine of 13 seronegative and nine of 12 seropositive myasthenics and in bone marrow lymphocytes (BML) from nine of 13 seronegative and eight of 12 seropositive myasthenics. The mean number of IgG anti-AchR ASC was lower for seronegative than for seropositive patients (P < 0.01 for PBL and P < 0.0001 for BML). In seropositive patients the mean number of IgG anti-AchR ASC was higher for BML than for PBL (P < 0.01); in seronegative patients it was not. IgG anti-prsmR ASC were detected in PBL from four of eight seronegative and six of eight seropositive myasthenics and in BML from three of eight seronegative and five of eight seropositive patients. The mean number of IgG-anti-prsmR ASC did not differ between seronegative and seropositive patients for PBL but for BML the value was higher for seropositive than for seronegative patients (P < 0.01). We conclude that seronegative myasthenia gravis is an autoimmune disease and that ASC to AchR and to prsmR are present both in the blood and the bone marrow in seronegative patients as in seropositive ones. A major difference between the groups lies in the significantly greater number of ASC found in the bone marrow in the seropositive cohort.