Challenges in diagnosing coexisting ocular myasthenia gravis and thyroid eye disease

Pearls & Oy-sters: Thyroid-Associated Ophthalmopathy and Transient Neuromuscular Junction Disorder Due to Graves Disease

The concomitant presentation of thyroid-associated ophthalmopathy (TAO) and ocular myasthenia gravis is well documented. In the course of Graves disease (GD), symptomatic transient neuromuscular junction disorder may occur due to the effect of thyroid hormones at the neuromuscular synapse. Diagnostic clues are the clinical and electrophysiologic remission synchronous with restoration of euthyroidism. Furthermore, the occurrence of thymic hyperplasia in GD poses further diagnostic and therapeutic considerations. These points are discussed in the case report of a 43-year-old male patient suffering from TAO and transient neuromuscular junction disorder due to GD.

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.

Diagnosing myasthenia gravis using orthoptic measurements: assessing extraocular muscle fatiguability

INTRODUCTION

Diagnosing ocular myasthenia gravis (MG) can be challenging because serum antibodies are often not detected. We aimed to explore whether determining extraocular muscle (EOM) weakness using orthoptic measures, including an adapted Hess chart examination, can aid in diagnosing MG.

METHODS

We conducted a prospective study among patients with acetylcholine receptor antibody positive MG (20 recently diagnosed, 19 chronic) and 14 seronegative MG patients. We compared orthoptic measures to 19 healthy and 18 disease controls with Graves orbitopathy, chronic progressive external ophthalmoplegia or oculopharyngeal muscular dystrophy. Maximal eye duction angles were measured using a synoptophore. Gaze deviations between eyes were measured using standard Hess chart examination with addition of 1 min persistent gaze to assess MG-associated fatiguability. Receiver operating characteristics curve analysis was performed.

RESULTS

For duction angles, the area under the curve (AUC) was 0.73 comparing MG to healthy, and 0.69 comparing to patient controls. For the outer field of the Hess chart, the AUC was 0.89 comparing to healthy and 0.54 to patient controls. For drift, the AUC was 0.93 comparing to healthy and 0.93 to patient controls. The sensitivity and specificity of the presence of drift was 81% and 100%.

DISCUSSION

Orthoptic measurements can be used to diagnose MG by quantifying EOM weakness and fatiguability. Drift during persistent gaze on a Hess chart is specific for MG and could be used for diagnostic purposes. The Hess chart examination is widely available, inexpensive and fast. Moreover, orthoptic measurements may be a clinically relevant outcome measure for clinical trials.

Eye Muscle MRI in Myasthenia Gravis and Other Neuromuscular Disorders

INTRODUCTION

MRI of extra-ocular muscles (EOM) in patients with myasthenia gravis (MG) could aid in diagnosis and provide insights in therapy-resistant ophthalmoplegia. We used quantitative MRI to study the EOM in MG, healthy and disease controls, including Graves' ophthalmopathy (GO), oculopharyngeal muscular dystrophy (OPMD) and chronic progressive external ophthalmoplegia (CPEO).

METHODS

Twenty recently diagnosed MG (59±19yrs), nineteen chronic MG (51±16yrs), fourteen seronegative MG (57±9yrs) and sixteen healthy controls (54±13yrs) were included. Six CPEO (49±14yrs), OPMD (62±10yrs) and GO patients (44±12yrs) served as disease controls. We quantified muscle fat fraction (FF), T2water and volume. Eye ductions and gaze deviations were assessed by synoptophore and Hess-charting.

RESULTS

Chronic, but not recent onset, MG patients showed volume increases (e.g. superior rectus and levator palpebrae [SR+LPS] 985±155 mm3 compared to 884±269 mm3 for healthy controls, p < 0.05). As expected, in CPEO volume was decreased (e.g. SR+LPS 602±193 mm3, p < 0.0001), and in GO volume was increased (e.g. SR+LPS 1419±457 mm3, p < 0.0001). FF was increased in chronic MG (e.g. medial rectus increased 0.017, p < 0.05). In CPEO and OPMD the FF was more severely increased. The severity of ophthalmoplegia did not correlate with EOM volume in MG, but did in CPEO and OPMD. No differences in T2water were found.

INTERPRETATION

We observed small increases in EOM volume and FF in chronic MG compared to healthy controls. Surprisingly, we found no atrophy in MG, even in patients with long-term ophthalmoplegia. This implies that even long-term ophthalmoplegia in MG does not lead to secondary structural myopathic changes precluding functional recovery.

Incidence and causes of overdiagnosis of myasthenia gravis

INTRODUCTION/AIMS

We have encountered non-myasthenic patients being given a diagnosis of myasthenia gravis (MG). This study aims to investigate the frequency of, and factors contributing to, overdiagnosis of MG.

METHODS

This is a retrospective analysis of patients referred to our tertiary neuromuscular center for evaluation due to a previously suspected/confirmed MG diagnosis during a 6-year span.

RESULTS

A total of 531 patients sought a second opinion regarding their MG diagnosis, and 77 (14.5%) were found to have non-myasthenic conditions. A total of 11 patients tested positive for acetylcholine receptor (AChR) antibodies. Repeated AChR antibodies became negative in five patients while in four patients, AChR binding antibody titers were persistently low. In seven patients, striational antibody was the only positive antibody identified. In 25 patients, a prior electrodiagnostic (EDX) study was deemed positive, including 14 patients with abnormal repetitive nerve stimulation (RNS) and 12 with abnormal single fiber electromyography (SFEMG). Technical issues were noted on prior RNS studies in 8 patients, and repeat RNS was negative in 10 patients. In eight patients with previously abnormal SFEMG, results showed minimal or equivocal abnormalities. In two patients, a repeat SFEMG was normal. Further analysis revealed atypical clinical presentation, deceptively positive ice pack test, clinically insignificant antibody result and misleading EDX finding as main contributors to MG overdiagnosis.

DISCUSSION

Overdiagnosis of MG is not uncommon, and occurs more frequently in seronegative patients. To make an accurate diagnosis of MG, there is a need to recognize atypical presentations, and avoid overreliance on minor or non-specific serological and electrodiagnostic findings.

Clinical and imaging clues to the diagnosis and follow-up of ptosis and ophthalmoparesis

Ophthalmoparesis and ptosis can be caused by a wide range of rare or more prevalent diseases, several of which can be successfully treated. In this review, we provide clues to aid in the diagnosis of these diseases, based on the clinical symptoms, the involvement pattern and imaging features of extra-ocular muscles (EOM). Dysfunction of EOM including the levator palpebrae can be due to muscle weakness, anatomical restrictions or pathology affecting the innervation. A comprehensive literature review was performed to find clinical and imaging clues for the diagnosis and follow-up of ptosis and ophthalmoparesis. We used five patterns as a framework for differential diagnostic reasoning and for pattern recognition in symptomatology, EOM involvement and imaging results of individual patients. The five patterns were characterized by the presence of combination of ptosis, ophthalmoparesis, diplopia, pain, proptosis, nystagmus, extra-orbital symptoms, symmetry or fluctuations in symptoms. Each pattern was linked to anatomical locations and either hereditary or acquired diseases. Hereditary muscle diseases often lead to ophthalmoparesis without diplopia as a predominant feature, while in acquired eye muscle diseases ophthalmoparesis is often asymmetrical and can be accompanied by proptosis and pain. Fluctuation is a hallmark of an acquired synaptic disease like myasthenia gravis. Nystagmus is indicative of a central nervous system lesion. Second, specific EOM involvement patterns can also provide valuable diagnostic clues. In hereditary muscle diseases like chronic progressive external ophthalmoplegia (CPEO) and oculo-pharyngeal muscular dystrophy (OPMD) the superior rectus is often involved. In neuropathic disease, the pattern of involvement of the EOM can be linked to specific cranial nerves. In myasthenia gravis this pattern is variable within patients over time. Lastly, orbital imaging can aid in the diagnosis. Fat replacement of the EOM is commonly observed in hereditary myopathic diseases, such as CPEO. In contrast, inflammation and volume increases are often observed in acquired muscle diseases such as Graves' orbitopathy. In diseases with ophthalmoparesis and ptosis specific patterns of clinical symptoms, the EOM involvement pattern and orbital imaging provide valuable information for diagnosis and could prove valuable in the follow-up of disease progression and the understanding of disease pathophysiology.

Post-COVID simultaneous onset of Graves' disease and ocular myasthenia gravis in a patient with a complex ocular motility impairment

A 74-years-old man experienced severe diplopia one month after recovery from an uncomplicated SARS-CoV-2 infection. Neurological examination was normal whereas ophthalmological examination showed bilateral exophthalmos with a complex ocular motility disorder characterized by a pseudo-internuclear ophthalmoplegia after fatigue associated to impairment of elevation and infraduction. Antibodies against TSH and acetylcholine receptors were positive; subsequent hormonal tests, ultrasonography of thyroid gland, single fiber electromyography and orbit MRI confirmed the diagnosis of concomitant Graves Disease (GD) and Myasthenia Gravis (MG). The coexistence between MG and GD is not rare but simultaneous onset after viral infection is very unsual. The complex ocular disorder simulated a deficit of the oculomotor nerve nuclei, and on clinical examination it posed some problems in the diagnosis. We suggest that recent SARS-COV-2 infection may have triggered a complex autoimmune response.