Diagnosis Of Ocular Myasthenia Research Articles

Ocular myasthenia

Myasthenia gravis is a chronic autoimmune neuromuscular disorder typically presenting with variable skeletal muscle fatigue. The most prevalent initial manifestation of myasthenia is ocular myasthenia. Approximately 50% of all myasthenia cases begin with the weakening of the eye muscles that generally presents as diplopia and/or ptosis. However, about 60% of these cases progress to a generalized type within the first 2 years. The diagnosis of ocular myasthenia is often difficult but is collectively confirmed by clinical evaluation and laboratory results.Clinical manifestations, diagnostic approach, relevance, and therapeutic options are discussed in this article.

Diagnostic accuracy and clinical utility of bed side tests versus laboratory tests in the diagnosis of ocular myasthenia.

Purpose:To assess the diagnostic accuracy of forced eyelid closure test (FECT), ice pack test (IPT), repetitive nerve stimulation test (RNS), and acetylcholine receptor (AchR) antibody test in patients with suspected ocular myasthenia. To assess the clinical utility of AchR antibody test in predicting disease progression.Methods:Retrospective cohort study of patients diagnosed with ocular myasthenia at a South-Indian neuro-ophthalmology tertiary eye clinic. Baseline characteristics; ocular myasthenia symptoms; results of FECT, IPT, RNS, and AchR antibody test; and progression time to generalized myasthenia (GM) over 36 months from the time of diagnosis were recorded and analyzed using receiver operator curve analysis, multiple logistic regression, and Kaplan–Meier survival analysis.Results:FECT had a sensitivity of 96.7% (95% CI: 88.5–99.6) and a specificity of 75% (95% CI: 34.9–96.8). Combination of FECT and IPT, using the positivity of at least one test, increased the sensitivity to 98.3% (95% CI: 91–100), reducing the specificity to 50% (95% CI: 15.7–84.3), whereas using the positivity of both tests, we obtained a sensitivity of 71.7% (95% CI: 58.6–82.5) and a specificity of 100% (95% CI: 63.1–100). In the subset of patients with double negative RNS and AchR antibodies, the positive predictive value of combined FECT and IPT (double positive) was 100%. Patients who developed GM were more likely to have a positive AchR antibody test result (P = 0.001)Conclusion:Combined FECT and IPT (double positive) has high diagnostic accuracy even among patients with normal RNS and negative AchR antibodies. Despite low sensitivity, AchR-antibody test has a significant predictive value in disease progression.

Author Response: Comparison of Ice Pack Test and Single-Fiber EMG Diagnostic Accuracy in Patients Referred for Myasthenic Ptosis.

We thank Dr. Silvestri for the comment on our article1 and agree that a relatively high proportion of patients showed discordant results between the ice pack test and single-fiber electromyography (SF-EMG) because they were observed in 15% of patients with a final diagnosis of ocular myasthenia (OM). Most of discordant cases were related to the negativity of the ice pack test in the presence of an altered SF-EMG result. One explanation could be the lack of repetition of the ice pack test, as we outlined in the discussion. Indeed, a previous study showed that repeated ice pack tests improved sensitivity by 34.6% compared with a single test.2 We also found that the repetition of the ice pack test in some patients increased its sensitivity and, therefore, the number of patients showing concordant results (unpublished data).

36. Sensitivity of single fibre electromyography in ocular myasthenia

The diagnosis of ocular myasthenia (OM) can be challenging due to the mildness of symptoms and to the absence of a gold diagnostic standard test. In several studies single fibre electromyography (SFEMG) showed a sensitivity of 0.86–0.99 for the diagnosis of OM. However these studies presented some methodological limitations. Our aim is to determine the diagnostic sensitivity of SFEMG in OM. We studied 157 consecutive patients diagnosed with OM on the basis of the presence of at least one of the following criteria: (1) positive edrophonium test; (2) abnormal repetitive nerve stimulation; (3) positive antiacetylcholine receptor antibodies; (4) improvement with corticosteroid therapy. Other diseases presenting with ptosis/diplopia were excluded. Stimulation SFEMG was performed on orbicularis oculi (S-SFEMG) in all cases and on the frontalis during voluntary activation (V-SFEMG) in 120 patients. In the whole population S-SFEMG was positive in 71% of cases whereas V-SFEMG was positive in 62% of cases. In patients with isolated ptosis (45%) S-SFEMG and V-SFEMG were positive in 87% and 85% of cases, respectively. In patients with isolated diplopia (31%) S-SFEMG and V-SFEMG resulted abnormal in 27% and 3% of patients, respectively. In patients with ptosis and diplopia (24%) both S-SFEMG and V-SFEMG were positive in 100% of cases. SFEMG showed a lower sensitivity than previously reported. However, sensitivity appears to be highly variable in relation with the clinical phenotype, being particularly low in patients presenting with isolated diplopia. S-SFEMG on orbicularis oculi is more sensitive than V-SFEMG on frontalis.

A clinical approach to ocular myasthenia gravis

Myasthenia gravis is a common disorder of the neuromuscular junction characterized clinically by muscle weakness and fatigability. Ocular myasthenia is often misdiagnosed in the initial stages due to the fluctuating nature of ptosis and diplopia. Here, we describe the clinical characteristics of ocular myasthenia gravis along with the diagnostic difficulties in a tertiary eye care center in Nepal. We retrospectively reviewed the charts of the patients diagnosed as ocular myasthenia gravis in Neuro-ophthalmology clinic, BPKLCOS, from 2010 to 2013. The diagnosis of ocular myasthenia was based on the association of typical history and signs together with at least one of these features: unequivocal improvement of ocular signs after injection of neostigmine, positive response to electrophysiological tests and detection of serum antibodies to acetylcholine receptors. There were 24 cases of diagnosed ocular myasthenia gravis during the 3 years. Among them 11 cases (45.8%) were males and 13 cases (54.1%) were females. The mean age was 32.04±19.56 years with the age range from 9 years to68 years. The most common symptoms among patients were drooping of the lids (45.8%, n=11), followed by both double vision and drooping of the lids (37.5%, n=9) and only intermittent double vision in16.6% (n=4). In two patients (9.09%) CT-scan findings were suggestive of thymoma. The symptoms were resolved with anticholinesterases alone in 66.6% (n=16) and anticholinesterases were supplemented with immunosuppressive drugs in 33.3% (n=8) patients. Ocular myasthenia is often misdiagnosed in the initial stages due to its fluctuating nature. With a high index of clinical suspicion simple clinical tests accompanied by pharmacological tests can be useful in diagnosing the condition.DOI: http://dx.doi.org/10.3126/jcmc.v4i3.11931Journal of Chitwan Medical College 2014; 4(3): 5-8

Stimulated single fiber EMG of the frontalis muscle in the diagnosis of ocular myasthenia.

We performed single fiber electromyography by axonal stimulation (SFEMG-AS) of the frontalis muscle of 16 patients with ocular myasthenia gravis (OM) and 33 controls. In the controls, values of mean consecutive differences (MCD) ranged from 5 to 55 micros (average, 14.7 +/- 2.8 micros) and mean MCD of individual MPs was 14. 6 +/- 6.8 micros. All the OM patients showed abnormal SFEMG-AS jitter before prostigmine was administered (mean MCD: 49.19 +/- 21. 82 micros, percentage of blocks: 20.97 +/- 18.53). Twenty or 30 min after prostigmine had been administered, we saw a significant improvement in jitter: mean MCD was 36.38 +/- 22.49 micros (P = 0. 005), and percentage of blocks was 10.16 +/- 18.87 (P = 0.008). The method was well tolerated. We conclude that SFEMG-AS of the frontalis muscle is a sensitive technique for the diagnosis of OM and is easy to carry out.

Ocular myasthenia: evaluation of Tensilon tonography and electronystagmography as diagnostic tests.

The value of electronystagmography (ENG) and of tonography in monitoring the beneficial effect of edrophonium chloride (Tensilon) on the extraocular muscles in myasthenia gravis has been assessed. Studies were performed on 17 patients with myasthenia gravis and on 18 control subjects, of whom nine had extraocular muscle weakness due to myopathic or neurogenic lesions.Electronystagmography recorded the repetitive following movements of the eyes elicited during optokinetic nystagmus. Neuromuscular fatigue with the subsequent beneficial response to Tensilon was clearly seen in 50% of patients with myasthenia. False positive responses were not seen in control subjects but in many of these, as in the remaining myasthenic patients, the amplitude and rate of nystagmus seen in the ENG was very variable. These difficulties suggest that the ENG is of limited value as a diagnostic test in myasthenia gravis.Tonography, recording the intraocular pressure of the eye continuously over four minutes, was found to be of considerable value. We found that the intraocular pressure fell on average by 1·6 to 1·8 mm Hg over a one minute period in the control recordings but increased by a mean of 1·6 mm Hg in patients with myasthenia, with a peak effect 35 seconds after Tensilon. In only one patient was there a complete failure of response. This patient, and also another woman who showed a less striking response, had severe myasthenia with a fixed ocular weakness. It is suggested that an absence of any increase in tension with Tensilon may be seen in patients with permanent neostigmine-resistant myopathic change. A small false positive response was seen on one occasion only in a patient with a sympathetic nerve lesion.Tensilon tonography, as a simple painless procedure, would appear to be of considerable value in the diagnosis of ocular myasthenia and also as a diagnostic test in the exclusion of myasthenia as a cause of isolated extraocular neuromuscular weakness.