Between September 2016 and July 2018, 98 MG patients diagnosed as moderate to severe myasthenia gravis, aged from 18 to 60 years old, were recruited from our hospital and outpatient clinic. The local ethics committee approved this study, and all patients signed a written consent form.
The following diagnostic criteria for MG were used: (a) clinical manifestations of myasthenia gravis, (b) positive AChR-ab, (c) positive response to anticholinesterases, and (d) abnormal neurophysiological findings (repetitive nerve stimulation and single-fiber electromyography). MG was diagnosed in patients fulfilling at least two of the four criteria.
Only patients with moderate to severe MG were enrolled (classified according to Myasthenia Gravis Foundation of America classification) [10] who are conscious, cooperating, and able to fulfill the questionnaire subjects.
Patient with congenital myasthenic syndrome, progressive restricted myopathies, steroid, and inflammatory myopathies, motor neuron disease, multiple sclerosis, variants of Guillain-Barré syndrome (such as Miller-Fisher syndrome), organophosphate toxicity, botulism, black widow spider venom, Eaton-Lambert syndrome, stroke and drug-induced myasthenia-like syndromes: neuromuscular blocking agents, aminoglycosides, penicillamine, antimalarial drugs, colistin, streptomycin, polymyxin B, and tetracycline were excluded from this study. Also, patients with contraindication to plasmapheresis, such as presence of a hemorrhage or surgical bleeding, tumors, acute inflammatory and infectious processes, extreme degree of heart failure, and significant hypotension, were excluded.
All patients were subjected to history taking including duration of their disease, symptoms, disability, and frequency of relapse and severity of their disease, number of crises, therapeutic interventions including thymectomy, use of cholinesterase inhibitors, steroids, and other immunosuppressant, the daily doses of various medications administered, comorbidities, history of other autoimmune diseases, and drug history.
Full neurological examination was done to all patients and repeated after 1 month and their quantitative MG (QMG) scores were calculated. The quantitative MG (QMG) score is used in clinical studies as a measure of disease severity. The validated scale is clinician administered and comprises 13 items that quantitatively assess the endurance or fatigability of different muscle groups, 27 taking into account the fluctuating nature of the disease. The items are as follows: ptosis, diplopia, orbicularis oculi weakness, swallowing a cup of water, speech, percent predicted forced vital capacity, grip strength (2 items), arm endurance (2 items), leg endurance (2 items), and neck flexion endurance. All items are scored on a scale of 0 to 3, and total scores range from 0 to 39; higher scores indicate greater disease severity. A ⩾3-point difference in the QMG score is considered clinically meaningful and scores of 10–16 and >16 indicate mild and moderate disease, respectively. 35 A change of 3.5 points in the total score is considered a clinically meaningful improvement for patients with MG.
Laboratory work was done including thyroid functions, other autoimmune disorders workup (erythrocyte sedimentation rate (ESR), antinumclear antibodies (ANA), anti-cytoplasmic nuclear antibodies (ANCA) anto RO, anti La, SLE, anticardiolipin antibodies), acetylcholine receptor antibodies (AChR-ab) using the enzyme-linked immune-sorbent assay technique. Computed tomography (CT) of the mediastinal region was also performed in all cases to search for thymus hyperplasia or thymoma.
Neurophysiological studies were done using Nemus, Biomedica, Model number 00655, Galileo NT software version 3.71/00, Italy, including repetitive nerve stimulation (RNS), single fiber EMG (SFEMG), and electromyography (EMG).
For RNS, surface electrodes are used, one over the belly of the muscle, the other at a position remote from the muscle. Low frequency stimulation is given by a surface electrode on the corresponding nerve at a rate of 2-3 Hz. Movements induced by the muscle contraction have to be prevented by convenient fixation. The negative amplitude of the first response is measured together with the relative difference between the fourth (or fifth) and first response. Test was considered abnormal when a “decremental pattern” was observed (decrement >11% of the fifth compound muscle action potential (CMAP) with respect to the first CMAP) of at least one proximal and one distal nerves innervating weak muscles [11].
Single fiber EMG (SFEMG) done in case RNS gave normal result. A needle electrode with a recording surface of 25 μm in diameter in a side port of the cannula is positioned in the voluntarily activated muscle to record activity from a few adjacent muscle fibers. We generally use the SFEMG reference values published in 1994 by the Ad Hoc Committee of the AAEM Single Fiber Special Interest Group [12].
Electromyography (EMG) done on proximal muscles of the limbs (deltoid, biceps brachii, rectus femori) was performed in all cases in order to evaluate myopathy.
Patients with moderate to severe MG were divided into two groups: (1) Patients admitted for a worsening of the disease (83 patients) and received plasmapheresis sets (five plasmapheresis procedures, performed every second day), but in this group, two patients had respiratory failure and died before completing the plasmapheresis sessions so only 81 patients included in the final statistical analysis. (2) Patients not receiving plasmapheresis sets and only on medical treatment, patients included in this group were patients who have a monthly follow-up schedule in outpatient clinics (17 patients).
A comprehensive explanation of both clinical efficacy and adverse effects of plasmapheresis was done to reduce the patients’ anxiety for the procedure. Central venous access was performed using a temporary dual-lumen catheter (Mahukar), with gage depending on patient size. Each patient received up to 5 plasmapheresis procedures.
Membrane filtration types were performed. Fifty milliliters of plasma/kg body weight/session was removed and an equivalent amount of solution containing albumin, 5%; sodium, 145 mEq/L; potassium, 3 mEq/L; calcium, 5 mEq/L; magnesium, 1.9 mEq/L; chloride, 115 mEq/L, and lactate, 35 mEq/L was reinfused. Then 0.5 g of 10% calcium gluconate was added directly to each 500-ml 5% albumin bottle to prevent citrate reactions. A bolus of 7500 IU of heparin/session was used as the anticoagulant. Average duration of each session was 5 h. No serious events were observed.
Quality of life (QoL) was assessed using Myasthenia Gravis Quality Of Life 15 (MG-QOL-15) score with the assistance of neurology doctors. This is a self-administered disease-specific questionnaire consisting of 15 items. Response to each item was scored on a scale of “0,” “1,” “2,” “3,” and “4” representing “not at all,” “a little bit,” “somewhat,” “quite a bit,” and “very much,” respectively. MG-QOL15 has a maximum score of 60, and there is no pre-specified cutoff for classifying the QOL of MG patients. The higher the MG-QOL15 score, the poorer the QOL [13,14,15]. Test was repeated after 1 month (2 weeks after finishing plasmapheresis) for the patient group.
The study was carried out in accordance with the Declaration of Helsinki and was approved by the Institute Ethics Committee before its commencement.
Data was collected, revised, coded, and entered to the Statistical Package for Social Science (IBM SPSS) version 23, Armonk, NY: IBM Corp. The quantitative data were presented as mean, standard deviations, and ranges when their distribution found parametric and median with interquartile range (IQR) when their distribution found non-parametric while qualitative data were presented as number and percentages. The comparison between two independent groups with qualitative data was done by using chi-square test. The comparison between two paired groups with quantitative data and parametric distribution was done by using paired t test while with non-parametric data was done by using Wilcoxon rank test. The comparison between more than two independent groups with quantitative data and parametric distribution was done by using one-way ANOVA while with non-parametric data was done by using Kruskal-Wallis test. Spearman correlation coefficients were used to assess the correlation between two quantitative parameters in the same group.