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Título

Clinical improvement in anti-MuSK myasthenia gravis patient after thymectomy – a case report

RESUMO

CASE PRESENTATION:
Female patient, 32 years old, presented eyelid ptosis to the right, diplopia, dysphonia and proximal appendicular weakness in superior members with floating characteristic. She was submitted to an electroneuromyography with repetitive stimulation (decremental pattern). The tomography of the chest showed thymic hyperplasia associated to the antireceptors antibody dosage of acetylcholine (AChR) negative, but anti-kinase antibody muscle-specific (MuSK) positive. She initiated the usage of prednisone up to 80mg/day and pyridostigmine reaching 360mg/day with partial response. Continued with the symptoms worsening, tachydyspnea and hospitalization in an intensive care unit. Medication adjustment was attempted without any improvement, besides developing Cushing’s syndrome secondary to the corticotherapy. Then a thymectomy was chosen. The patient presented diaphragmatic paralysis after the thymectomy, and a diaphragmatic plication was carried out with clinical improvement. The weaning of the corticotherapy was initiated. After six months she is found using exclusively prednisone 5mg/day and without myasthenic symptoms.
DISCUSSION:
Myasthenia gravis (MG) is an autoimmune disorder of the neuromuscular junction hallmarked by motor fluctuations (fatiguability). Treatment options are acetylcholinesterase inhibitors, glucocorticoids, immunoglobulin, plasmapheresis, immunosuppressives and monoclonal antibodies (eculizumab). The antibodies for the diagnosis are anti-AChR, anti-MuSK and anti-protein related to the lipoprotein 4 (LRP4). The thymectomy is indicated based on the flaw of the thymic recognition function and negative selection of autoreactive T cells – physiopathology implied mechanism of mediated MG AChR (MG-AChR). The thymectomy is indicated on thymic persistence or on thymoma presence, when is performed the mediastinal toilet. Not long ago thymectomy was not indicated in anti-MuSK positive cases, but the last updates do not define thymectomy as a resource or contraindicate. Interestingly, in this case, despite thymectomy’s possible inefficacy for anti-MuSK positive patients, an unequivocally improvement and corticoids/pyridostigmine dosage reduction was observed after the thymectomy.
FINAL COMMENTS: The success of the therapeutic response after the thymectomy on an anti-MuSK positive patient puts in discussion the debate about thymectomy as a therapeutic weapon in myasthenic anti-MuSK positive patients with persistent thymus/ thymoma.