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Resistant Myasthenia gravis with Rituximab and Re-thymectomy approach: Case Report

RESUMO

Case presentation: A 32-year-old patient, female, previously healthy, presented to this service in 2016, implying bulbar musculature weakness with dysphagia and dysarthria. Due to the fatigability pattern of bulbar musculature, there was a diagnostic suspicion for Myasthenia gravis, which was later confirmed by humoral dosage of anti-AchR (61) with negative anti-MusK. Subsequently, despite optimizing measures adopted, such as Intravenous Methylprednisolone (IVMP) pulse therapy, acetylcholinesterase inhibitors, and Intravenous Immunoglobulin (IVIG), the patient presented progressive clinical worsening with consequent respiratory failure suitably to diaphragmatic loss (Osserman Classification V). Therefore, properly to refractoriness of previous measures, specialists recommended a Video-assisted Thoracoscopic Surgery (VATS) excision and histopathological analysis of the thymus, as it is associated with possible humoral hypersecretion and consequent development of cross-reactions and autoimmune lesions. As a result, the Immunohistochemical Profile (IP) evidenced thymic hyperplasia without atypia. However, after the procedure, the patient remained with muscle fatigability requiring clinical control through Azathioprine and immunotherapy with Rituximab - since there is no availability of the monoclonal antibody Eculizumab at our disposal. Then, we proposed a second approach to investigate ectopic tissue with complete resection of pericardial and mediastinal fat. The analysis showed a small aggregate of lymphoid tissue in re-thymectomy. Since then, the patient has had adequate clinical therapy, maintaining optimized doses according to guidelines for fatigability control.

Discussion: Myasthenia gravis is a neuromuscular transmission disorder resulting from the binding of autoantibodies to components of the neuromuscular junction (NMJ), most commonly the acetylcholine receptor (AChR). These autoantibodies are directly responsible for the pathological change in the endplate - being dependent on CD4+ T and B cells. Multicentric trials recommend a sternotomy approach with en bloc resection of all mediastinal tissue. This occurs due to microscopic thymic components that are not macroscopically identifiable. A focused and conservative approach remains in question.

Conclusion: In this presentation, we describe a patient with resistant Myasthenia gravis, leaving the usual pattern of clinical control and suggesting the importance of the thymus in the pathophysiology.

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Doenças Neuromusculares