Miastenia gravis: estudo clínico e neurofisiológico de 97 pacientes

Abstract

Myasthenia Gravis (MG) is an autoimmune disease, defined by the presence of antibodies to the components of the post-synaptic membrane of the neuromuscular junction. Antibodies to the acetylcholine receptors (anti-AChRs) and muscle-specific tyrosine kinase (anti-MuSK) are the most frequently found. Objective: To describe epidemiological data, disease's initial presentation and its outcome, antibodies test, repetitive nerve stimulation (RNS), single-fiber electromyography (SFEMG), and thymus pathology in cases of thymectomy. Material and Methods: The study design was a descriptive, observational, and retrospective review of 97 MG patients followed at the Neuromuscular Disorders Outpatient Clinic of the Hospital de Base, State Medical School of São José do Rio Preto, SP (FAMERP). In addition to the variables described, it has also evaluated the patients' outcomes, the conventional treatment, the number of myasthenic crises, and the post-intervention status (drug treatment with or without thymectomy). Results: Fifty-two patients (53.6%) were male. The mean age of the onset of the symptoms was 43 years. The mean time to diagnosis was 43.4 months. Ocular MG form (OMG) was observed in 12.4%, and generalized MG form (GMG) in 87.6%. The myasthenic crisis was observed in 21.6%. Sixty-two patients (63.9%) had the early form of the disease, and the late form in 36.1%. Abnormal values of the anti-AChRs were found in 84.5%, with an average value of 14.14 ± 21.05 nmol/L. Abnormal values of the anti-Musk were found in 2.1%. Abnormal values of non-specific striated antibodies were found in 22.9%. Abnormal decrement (>10%) in some nerve-muscle was observed in 78.4%. Some abnormal jitter parameter was found in 93.8%. Forty-seven patients (48.5%) underwent thymectomy. Thymoma was found in 19 patients (19.6% of total) and hyperplasia in 16 (16.5% of total). OMG patients had anti-AChRs with a mean of 1.83 nmol/L, while patients with GMG form had 16.9 nmol/L. Abnormal decrement was found in 25% of the OMG and 85.9% of the GMG. Some abnormal jitter parameter was found in all the OMG cases and 92.9% of the GMG. Sixty-nine patients (88.5%) had a favorable outcome during follow-up. Conclusion: There was a slight predominance in males. Abnormal jitter was observed in 93.8%, followed by abnormal antibody titer (86.6%) and abnormal decrement (78.4%). All OMG cases had abnormal jitter when two facial muscles were tested. Jitter > 86 μs was only found in GMG. The mean anti-AChRs values and the mean decrement were significantly lower in the OMG. The percentage of patients with a favorable outcome was high; with no casualties.