Factors affecting outcome in ocular myasthenia gravis

Aim of the study: 50%–60% of patients with ocular myasthenia gravis (OMG) progress to generalized myasthenia gravis (GMG) within two years. The aim of our study was to explore factors affecting prognosis of OMG and to test the predictive role of several independent clinical variables.

Materials and methods: We reviewed a cohort of 168 Caucasian patients followed from September 2000 to January 2016. Several independent variables were considered as prognostic factors: gender, age of onset, results on electrophysiological tests, presence and level of antibodies against acetylcholine receptors (AChR Abs), treatments, thymic abnormalities. The primary outcome was the progression to GMG and/or the presence of bulbar symptoms. Secondary outcomes were either achievement of sustained minimal manifestation status or worsening in ocular quantitative MG subscore (O-QMGS) or worsening in total QMG score (T-QMGS), assessed by Myasthenia Gravis Foundation of America (MGFA) quantitative scores. Changes in mental and physical subscores of health-related quality of life (HRQoL) were assessed with SF-36 questionnaire. Variance analysis was used to interpret the differences between AChR Ab titers at different times of follow up among the generalized and non-generalized patients.

Results: Conversion to GMG occurred in 18.4% of patients; it was significantly associated with sex, later onset of disease and anti-AChR Ab positivity. Antibody titer above the mean value of 25.8 pmol/mL showed no significant effect on generalization. Sex and late onset of disease significantly affected T-QMGS worsening. None of the other independent variables significantly affected O-QMGS and HRQoL.

Conclusions: Sex, later onset and anti-AChR Ab positivity were significantly associated with clinical worsening.     

Atypical ocular myasthenia gravis

The diagnosis of ocular myasthenia gravis is rarely in doubt in patients with a proper history and typical clinical findings. However, myasthenia gravis can mimick any pupil-sparing eye movement disorder and several diseases may masquerade myasthenia gravis. We review the atypical presentations and differential diagnoses in ocular myasthenia gravis, describing four patients with some of these conditions (4th nerve palsy, near spasm reflex, one-and-a-half syndrome, orbital meningioma). The correct interpretation of the clinical findings associated with appropriate neuro-imaging studies allowed the appropriate diagnosis in these cases.     

Therapeutic options in ocular myasthenia gravis

The term ocular myasthenia gravis refers to the disease clinically restricted to extrinsic ocular muscles. It can be disabling as ptosis, and to a greater extent diplopia, both interfere with daily activities. Although ocular disturbances are the most frequent initial complaints in myasthenic patients, symptoms usually progress to generalized disease and only 15% of patients complain of purely ocular weakness for the entire course of their illness. Secondary generalization occurs with the highest frequency in the first 2 years from the onset. Both the severity of symptoms and the risk of generalization should be taken into account when devising a therapeutic plan for these patients. Anticholinesterases are of limited efficacy and a considerable proportion of patients require additional therapy. Corticosteroid therapy, generally prednisone on an alternate-day schedule, is very effective, but a reason for concern is represented by the frequent need for long-term administration with increased risk of severe complications. In patients unresponsive to prednisone or requiring too high dosages, immunosuppressive drugs like azathioprine should be used with the same criteria applied in generalized myasthenia. As corticosteroids and immunosuppressants reduce the chance of generalization, their use is justified in patients with recent-onset disabling disease. In long-standing cases with low risk of generalization, treatment is aimed at the relief of symptoms and pharmacological therapy should be reduced to the minimum effective dosage. The indication for thymectomy in ocular myasthenia remains highly controversial and should be reserved for disabled patients in the early stages of the disease.     

Statins may aggravate myasthenia gravis

Statin-induced myopathy is well-known, but the effect of cholesterol-lowering agents on myasthenia gravis (MG) has not been studied in detail. We investigated statin use and its effects on MG among patients with this disease. Statin information was systemically obtained from 170 patients being treated at the Neuromuscular Disease Clinic at the University of Alabama at Birmingham. When a new myalgic syndrome or worsening of MG developed within 4 months after statin treatment, no other likely cause was found, and clinical improvement occurred either with or without discontinuation of the statin, we considered these symptoms to be statin-induced. Fifty-four patients (31%) were on statins. The statin group had proportionally more males, and older patients compared with the non-statin group. A myalgic syndrome was noted in 7 (13%) patients, but it resolved without any sequelae after withdrawal of the statin. MG worsening occurred in 6 (11%) patients without regard to type of MG or brand of statin. MG worsening occurred independently of myalgic syndrome and involved predominantly oculobulbar symptoms within 1-16 weeks of statin treatment. In 4 patients, additional treatment was needed to reverse MG worsening. Statins are safe in the majority of MG patients, but their use must be accompanied by close observation for possible MG worsening.     

眼肌型重症肌无力进展为全身型重症肌无力的临床相关因素分析

目的 :探讨眼肌型重症肌无力进展为全身型重症肌无力的临床相关预测因素。方法 :33例初诊为眼肌型重症肌无力的患者经过3年随访,根据疾病进展结局分为眼肌型重症肌无力组(13例)和进展为全身型重症肌无力组(20例)。对与疾病进展可能相关的临床因素进行分析。结果 :进展为全身型重症肌无力组患者初诊时的定量重症肌无力评分、乙酰胆碱受体抗体阳性率、抗核抗体阳性率、合并胸腺瘤的比例以及合并糖尿病的比例均高于眼肌型重症肌无力组(P值均0.05)。结论 :定量重症肌无力评分高、乙酰胆碱受体抗体阳性、抗核抗体阳性以及合并胸腺瘤和糖尿病可能是眼肌型重症肌无力进展为全身型重症肌无力的预测指标。     

Evoked EMG in juvenile ocular myasthenia gravis

We studied juvenile ocular myasthenia gravis (MG) with special reference to evoked EMG in orbicularis oculi muscle. The subjects consisted of 5 cases aged 1-4 years and 3 cases over 10 years. Young children were examined during drug-induced sleep. Stimulation was delivered to preauricular facial nerve, and M waves were recorded from ipsilateral orbicularis oculi muscle. Examinations were also carried out in thenar or hypothenar muscles by stimulating the median or ulnar nerves respectively. On Harvey-Masland test, 6 out of 8 cases showed waning of more than 10%. On M-wave recovery cycle, 3 out of 6 cases examined showed decrement during stimulation interval of 100 msec to 500 msec. In 2 of these, the peak of recovery cycle curve rose over 100% during stimulation interval of 30 to 60 msec on a usual dose treatment of anti-cholinesterase, while on prednisolone treatment this peak did not increase over 100% and the pattern of recovery cycle changed to almost normal. On post-tetanic cycle study, only 1 out of 4 cases examined showed post-tetanic facilitation and exhaustion. The response of the belly-tendon in the hand showed no abnormality. Although there still remains technical difficulty in the examination of evoked EMG in orbicularis oculi muscle, this examination is very useful in diagnosis, evaluation and understanding of pathophysiology of MG.     

眼肌型重症肌无力临床分析

目的总结分析眼肌型重症肌无力患者的临床特征,以为诊断和治疗提供参考依据。方法回顾性分析113例眼肌型重症肌无力患者的临床资料。采用免疫荧光细胞染色方法检测血清乙酰胆碱受体（AChR）抗体和肌肉特异性受体酪氨酸激酶（MuSK）抗体表达水平,分析这两项免疫学指标对眼肌型重症肌无力向全身型转化的预测价值。结果成年发病的眼肌型重症肌无力好发于40岁以上男性,多以眼睑下垂（95例,84．07％）为首发症状,少数以复视（18例,15．93％）起病。疲劳试验和新斯的明试验阳性率分别为79．44％（85／107）和84．85％（84／99）．低频重复神经电刺激和血清甲状腺抗体异常率分别为44．32％（39／88）和28％（14／50）,胸腺增生和胸腺瘤阳性率分别为16．67％（17／102）和11．76％（12／102）;血清AChR抗体阳性率为62.83％（71／113）;但MuSK抗体均呈阴性。眼肌型重症肌无力向全身型转化率为12．39％（14／113）,其中血清AChR抗体强阳性者（13例,28．26％）显著高于弱阳性者（1例,4％）,二者差异有统计学意义（X^2=4．587,P=0．032）。结论成年发病的眼肌型重症肌无力好发于中年以上男性,主要表现为眼睑下垂和复视,大多数患者伴发胸腺和甲状腺异常。血清AChR抗体表达水平升高预示向全身型转化率升高,鲜有MuSK抗体阳性反应。     

眼肌型重症肌无力临床分析

目的总结分析眼肌型重症肌无力患者的临床特征,以为诊断和治疗提供参考依据。方法回顾性分析113例眼肌型重症肌无力患者的临床资料。采用免疫荧光细胞染色方法检测血清乙酰胆碱受体(AChR)抗体和肌肉特异性受体酪氨酸激酶(MuSK)抗体表达水平,分析这两项免疫学指标对眼肌型重症肌无力向全身型转化的预测价值。结果成年发病的眼肌型重症肌无力好发于40岁以上男性,多以眼睑下垂(95例,84.07%)为首发症状,少数以复视(18例,1 5.93%)起病。疲劳试验和新斯的明试验阳性率分别为79.44%(85/107)和84.85%(84/99),低频重复神经电刺激和血清甲状腺抗体异常率分别为44.32%(39/88)和28%(14/50),胸腺增生和胸腺瘤阳性率分别为16.67%(17/102)和11.76%(12/102);血清AChR抗体阳性率为62.83%(71/113);但MuSK抗体均呈阴性。眼肌型重症肌无力向全身型转化率为12.39%(14/113),其中血清AChR抗体强阳性者(13例,28.26%)显著高于弱阳性者(1例,4%),二者差异有统计学意义(X~2=4.587,P=0.032)。结论成年发病的眼肌型重症肌无力好发于中年以上男性,主要表现为眼睑下垂和复视,大多数患者伴发胸腺和甲状腺异常。血清AChR抗体表达水平升高预示向全身型转化率升高,鲜有MuSK抗体阳性反应。     

SFEMG in ocular myasthenia gravis diagnosis.

BACKGROUND AND OBJECTIVE: In typical cases, the patient's history and clinical examination make it possible to diagnose ocular myasthenia gravis (OMG). But, in many cases a clear clinical picture is not present and OMG diagnosis is very difficult because gold diagnostic standard tests are not available. The diagnostic tests for OMG are usually unable to display a good sensitivity and specificity simultaneously. In this paper, we studied 86 cases submitted for suspected OMG. METHODS: The patients were studied clinically and with various other tests used in OMG diagnosis (SFEMG, repetitive nerve stimulation, Ab anti AChR titration, tensilon test). RESULTS AND CONCLUSION: SFEMG showed the highest sensitivity (100%) while Ab anti AChR showed the highest specificity (100%). To our knowledge this is the largest population of suspected OMG studied using most of the diagnostic parameters, reported in the literature.     

Autoimmunity in ocular and generalised myasthenia gravis

Restricted ocular myasthenia gravis (OMG) and generalised myasthenia gravis (GMG) have been shown to differ in a number of respects. In OMG, anti-acetylcholine receptor, antistriational and antinuclear antibodies were rare relative to their frequency in GMG. In contrast, antithyroid antibodies and a history of thyroid disease were much more prevalent in OMG than in GMG. OMG was not associated with the female predominance seen in GMG and appeared to be relatively common in some races rather than others. It is suggested that different pathogenetic mechnisms are responsible for these two forms of MG.     

Gabapentin may be hazardous in myasthenia gravis

A patient with painful neuropathy developed ocular, facial, and masticatory weakness and fatigue after 3 months of gabapentin (GBP) treatment (400 mg/day). An elevated level of serum acetylcholine receptor antibodies (AChR-Ab) was detected. The patient recovered following pyridostigmine therapy and withdrawal of GBP and, 2 years later, is practically asymptomatic despite positive AChR-Ab. Because of this clinical observation, we gave 150 mg/kg GBP to rats with experimental autoimmune myasthenia gravis (EAMG). Repetitive nerve stimulation at 3-Hz was performed, and the 5th/1st amplitude ratio was used to calculate the decremental response. In all EAMG rats, GBP induced a transient, abnormal decrement (7-20%) 90 to 240 min after administration. No decrement was induced by GBP in normal rats. Thus, GBP aggravates the decrement in EAMG. The mechanism involved in the hitherto unreported possible unmasking of myasthenia gravis (MG) by GBP is unknown. Gabapentin should be used with caution in this disease.     

Myasthenia gravis: Antibodies to acetylcholine receptor in ocular myasthenia gravis

Summary To improve the sensitivity of the radioimmunoassay method for anti-AChR-antibody, large amounts of sera from patients with myasthenia gravis, and higher concentrations of antigens and rabbit anti-human-IgG-antiserum, were used. These procedures enabled measurement of the titre value of over 0.04 pmol/ml serum and this value revealed a sensitivity about 10 times higher than that predicted using the previous model.Antibodies against AChR were found in 13 out of 17 ocular myasthenia patients (70%) and 35 of 37 with generalized myasthenia (90%). However, the average titre value of sera in those with ocular myasthenia was significantly lower than the value obtained in the generalized cases. Even in the patients with ptosis or ophthalmoparesis, in the early stage (less than one year) of ocular myasthenia, anti-AChR-antibodies were not detectable using this more sensitive assay method.

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Zusammenfassung Um die Empfindlichkeit der Radioimmunoassay-Methode für Anti-AChR-Antikörper zu verbessern, wurden eine große Menge des myasthenischen Serums, höhere Konzentration des Antigens und Kaninchen-Anti-Menschen-IgG-Antiserum gebraucht.Mit dieser Methode konnten wir den Wert über 0.04 pmol/ml Serum vermessen. Diese neue Methode zeigt etwa zehnfach höhere Empfindlichkeit als die vergangenen Methoden.Antikörper gegen AChR waren in 13 von 17 okulären Myastheniepatienten (70%) und in 35 von 37 generalisierten Myastheniepatienten (90%) gefunden worden. Aber der durchschnittliche Messungswert des Serums im Patienten der okulären Form war signifikant niedriger als der der generlisierten Form. Wenn der Patient auch Augenptose oder Augenparese hatte, waren die Anti-AChR-Antikörper mit unserer empfindlichen Methode im Frühstadium (innerhalb eines Jahres) nicht nachgewiesen worden.

     

不典型眼肌型重症肌无力的临床特点

目的研究不典型眼肌型重症肌无力(OMG)的临床特点。方法回顾性分析29例不典型OMG患者的临床资料。结果本组患者表现为上眼睑下垂3例,单眼1条眼外肌瘫痪15例,双眼3条眼外肌瘫痪1例,单眼全部眼外肌瘫痪1例,辐辏障碍2例,单眼眼轮匝肌瘫痪1例,类似眼病表现6例(复视4例、眼部不适和视物模糊2例,均无眼外肌瘫痪);有晨轻暮重表现12例(41.4%)。新斯的明试验阳性26例(89.7%),低频重复神经电刺激阳性8例(27.6%),单纤维肌电图(SFEMG)异常23例(79.3%)。患者早期均被误诊。经泼尼松和/或胆碱酯酶抑制剂治疗,症状消失26例(89.7%),显著改善3例(10.3%)。结论不典型OMG患者的临床特点为受累眼肌少,症状局限,表现晨轻暮重的比率低。新斯的明试验和SFEMG检查可确诊。     

眼肌无力的诊断及依据

重症肌无力是乙酰胆碱受体抗体介导的,细胞免疫依赖及补体参与的神经-肌肉接头处（NMJ）传递障碍的自身免疫性疾病。眼肌症状是最为多见的首发症状,表现为上眼睑下垂、复视、斜视等,尤以眼睑下垂最多。通过典型的临床表现及临床实验即可诊断、腾喜龙试验、血清抗体检测、电子诊断可以进一步确诊。