Test-Retest Reliability of Repetitive Ocular Vestibular Evoked Myogenic Potentials in Myasthenia Gravis Patients and Healthy Control Subjects

PURPOSE

Repetitive ocular vestibular evoked myogenic potentials (ROVEMP) are a novel diagnostic test to quantify neuromuscular transmission deficits in extraocular muscles in myasthenia gravis. We aimed to investigate the test-retest reliability of the ROVEMP and the effect of amplitude and age.

METHODS

We performed the ROVEMP test twice in 19 patients with myasthenia gravis (52.7 ± 19.8 years) and in 15 healthy control subjects (46.5 ± 16 years). The Bland-Altman level of agreement was determined. The relationship between test-retest reliability and signal quality, participant age and signal amplitude was studied.

RESULTS

Limits of agreement were from -179.9 to 139.3 in myasthenia gravis patients and from -56.9 to 89.5 in healthy control subjects. Difference between measurements correlated with signal amplitude ( r = -0.50, P < 0.001). Combining the primary cohort with previously published data from 114 subjects, we found a significant negative correlation between age and reference amplitude ( r = -0.163, P = 0.045).

CONCLUSIONS

This study shows that in our hands, the test-retest reliability of the ROVEMP is not optimal. Measurements with higher reference amplitude had a better quality, higher reproducibility, and increased diagnostic yield. We caution against the use of ROVEMP measurements of lower amplitude in clinical practice. In addition, given the correlation between age and amplitude, age matching of healthy control subjects and patients is essential in future studies.

Accuracy of patient-reported data for an online patient registry of autoimmune myasthenia gravis and Lambert-Eaton myasthenic syndrome

Disorders of the neuromuscular junction (NMJ) comprise a spectrum of rare diseases causing muscle fatigability and weakness, leading to life-long effects on quality of life. We established the Dutch-Belgian registry for NMJ disorders, based on a unique combination of patient- and physician-reported information. Information on natural course, disease burden, prevalence of complications and comorbidity is collected through patient-reported standardized questionnaires and verified using medical documentation. Currently, the registry contains information of 565 Myasthenia Gravis (MG) patients and 38 Lambert-Eaton myasthenic syndrome (LEMS) patients, constituting approximately 25% (MG) and 80% (LEMS) of patients in the Netherlands. This is a very large registry, with the highest participation rate per capita. In addition to confirming many disease characteristics previously described in the literature, this registry provides several novel insights. The reported rate of potentially corticosteroid-related comorbidity, including hypertension, heart disease, osteoporosis and type 2 diabetes was high, emphasizing the need to commence corticosteroid-sparing immune suppressive treatment as soon as possible. The reported rate of other auto-immune diseases is far higher than previously expected: 27% of MG and 38% of LEMS patients, and a surprisingly high number of MG patients (47%) is unaware of their antibody status. In conclusion, this registry provides a valuable collection of information regarding MG and LEMS disease course. Continuous collection of annual follow-up data will provide further longitudinal insights in disease burden, course and treatment effect.

Repetitive ocular vestibular evoked myogenic potentials in myasthenia gravis

OBJECTIVE

To validate the repetitive ocular vestibular evoked myogenic potentials (RoVEMP) test for diagnostic use in myasthenia gravis (MG) and to investigate its value in diagnostically challenging subgroups.

METHODS

The RoVEMP test was performed in 92 patients with MG, 22 healthy controls, 33 patients with a neuromuscular disease other than MG (neuromuscular controls), 4 patients with Lambert-Eaton myasthenic syndrome, and 2 patients with congenital myasthenic syndrome.

RESULTS

Mean decrement was significantly higher in patients with MG (28.4% ± 32.2) than in healthy controls (3.2% ± 13.9; p < 0.001) or neuromuscular controls (3.8% ± 26.9; p < 0.001). With neuromuscular controls as reference, a cutoff of ≥14.3% resulted in a sensitivity of 67% and a specificity of 82%. The sensitivity of the RoVEMP test was 80% in ocular MG and 63% in generalized MG. The RoVEMP test was positive in 6 of 7 patients with seronegative MG (SNMG) with isolated ocular weakness. Of 10 patients with SNMG with negative repetitive nerve stimulation (RNS) results, 73% had an abnormal RoVEMP test. The magnitude of decrement was correlated with the time since the last intake of pyridostigmine (B = 5.40; p = 0.019).

CONCLUSIONS

The RoVEMP test is a new neurophysiologic test that, in contrast to RNS and single-fiber EMG, is able to measure neuromuscular transmission of extraocular muscles, which are the most affected muscles in MG. Especially in diagnostically challenging patients with negative antibody tests, negative RNS results, and isolated ocular muscle weakness, the RoVEMP test has a clear added value in supporting the diagnosis of MG.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that RoVEMP distinguishes MG from other neuromuscular diseases.

Myasthenia Gravis Impairment Index: Sensitivity for Change in Generalized Muscle Weakness

INTRODUCTION

The recently developed Myasthenia Gravis Impairment Index (MGII) is a promising measure as it has less floor effects and a higher relative efficiency in its responsiveness to treatment effect compared to other MG measures. This study aimed at validating the MGII in a Dutch cohort of MG patients and analyzing the sensitivity of MGII compared to MG-ADL for changes in generalized weakness.

METHODS

We analyzed (generalized items of; -gen) MGII, quantitative myasthenia gravis (QMG), Myasthenia Gravis Activities of Daily Living (MG-ADL), EQ-5D visual analog, Myasthenia Gravis Composite (MGC) and ACTIVLIM (an ADL questionnaire focusing on generalized weakness) scores in a prospective cohort of 99 MG patients. We investigated correlations between MGII and other outcome measures. We used a generalized linear model to assess whether MGIIgen had an additional sensitivity on top of MG-ADLgen for changes (Δ) in QMGgen in individual patients.

RESULTS

MGII had a lower floor effect (4%) compared to QMG (6%), MG-ADL (11%) and MGC (16%). MGII correlated well with QMG (r = 0.68), MG-ADL (r = 0.83) and MGC (r = 0.74). As expected, the correlations with EQ visual analog and ACTIVLIM were lower (r = - 0.57 and - 0.48). ΔMGIIgen had an additional value on top of ΔMG-ADLgen in the prediction of ΔQMGgen (B = 0.54, p = 0.01).

DISCUSSION

The MGII score was cross-culturally validated in a Dutch cohort of MG patients. MGII had a higher sensitivity for generalized weakness than MG-ADL.

Ocular Weakness in Myasthenia Gravis: Changes in Affected Muscles are a Distinct Clinical Feature

Introduction:

In this study we quantitatively describe ocular weakness patterns in myasthenia gravis (MG) to help neurologists in making the clinical diagnosis and to investigate how the current outcome measures reflect ocular weakness in MG.

Methods:

We investigated ptosis and diplopia patterns in a retro- and prospective cohort of 306 MG patients. Diplopia was systematically examined by testing extra-ocular muscle (EOM) fatigability in two horizontal and four oblique directions for 60 seconds.

Results:

Of patients with initial symmetric ptosis, 40% developed asymmetric ptosis at the second visit. Changes in form of ptosis occurred less often in seronegative MG patients (50%) than in patients with acetylcholine receptor (AChR) antibodies (70%) or muscle-specific kinase (MuSK) antibodies (69%) (p = 0.038). Of patients with diplopia on the first visit, double vision contained both a vertical and horizontal component in 95%. At the second visit, 83% manifested diplopia in other gaze directions. The mean time (in seconds) to diplopia was 11.6±14.0 and the mean time to ptosis was 27.6±19.8. Diplopia or ptosis manifested within 30 seconds in 87% and 58%, respectively. Patients who manifested diplopia after 30 seconds, reported no limitations due to diplopia.

Discussion:

Changes in the gaze directions in which diplopia occurs or ptosis side occur frequently in MG. In diagnostically challenging cases, we recommend testing ptosis and diplopia in multiple gaze directions for 30–60 seconds during at least two follow-up visits to maximize the chance of observing changes in ocular weakness patterns.

A prospective, double-blind, randomized, placebo-controlled study on the efficacy and safety of influenza vaccination in myasthenia gravis

OBJECTIVE

To investigate the efficacy and safety of an influenza vaccination in patients with myasthenia gravis with acetylcholine receptor antibodies (AChR MG).

METHODS

An influenza vaccination or placebo was administered to 47 AChR MG patients. Before and 4 weeks after administration blood samples and clinical outcome scores were obtained. Antibodies to the vaccine strains A/California/7/2009 (H1N1)pdm09, A/Hong Kong/4801/14 (H3N2) and B/Brisbane/060/08 were measured using the hemagglutination-inhibition (HI) assay and disease-specific AChR antibody titers were measured with a radio-immunoprecipitation assay. Forty-seven healthy controls (HC) were vaccinated with the same influenza vaccine to compare antibody titers.

RESULTS

A post-vaccination, seroprotective titer (HI ≥ 1:40) was achieved in 89.4% of MG patients vs. 93.6% in healthy controls for the H3N2 strain, 95.7% vs 97.9% for the H1N1 strain and 46.8 vs 51% for the B-strain. A seroprotective titer for all three strains of the seasonal influenza vaccine was reached in 40.4% (19/47) of the MG group and in 51% (24/47) of the HC group. Immunosuppressive medication did not significantly influence post geomean titers (GMT). The titers of disease-specific AChR antibodies were unchanged 4 weeks after vaccination. The clinical outcome scores showed no exacerbation of MG symptoms.

CONCLUSION

The antibody response to an influenza vaccination in patients with AChR MG was not different from that in healthy subjects, even in AChR MG patients using immunosuppressive medication. Influenza vaccination does not induce an immunological or clinical exacerbation of AChR MG.

CLINICAL TRIAL REGISTRY

The influenza trial is listed on clinicaltrialsregister.eu under 2016-003138-26.