Thymic Neoplasm: A Rare Disease With Unusual Neurologic Manifestations

Thymoma is a rare tumor that is commonly associated with autoimmune diseases. Of these, myasthenia gravis (MG) is widely considered as the most common paraneoplastic condition. On the other hand, dermatomyositis (DM) has been rarely reported as the first presentation of non-invasive thymoma. Hereby, we describe a patient with non-invasive thymoma who initially presented with painful symmetric proximal muscle weakness with no signs of ptosis or diplopia. The needle electromyography (EMG) revealed spontaneous/insertional activity in proximal muscles. The patient was finally diagnosed with DM by muscle biopsy. Spiral chest computed tomography (CT) scan coupled with pathological assessment confirmed a non-invasive thymoma with diffuse reaction for P63 and pancytokeratin (Panck). Corticosteroids pulse therapy was initiated and the patient was referred for thymectomy. A few months later, patient began to display other neurological symptoms such as ptosis and diplopia with fluctuating pattern. As coexistence of MG was presumed, nerve conduction study (NCS) study was performed and slow repetitive nerve stimulation in proximal muscles showed more than 10% decrement in compound muscle action potential (CMAP) amplitude in repetitive nerve stimulation (RNS). Further workup revealed a positive anti-acetylcholine receptor antibody with high titer. Thus, MG was confirmed. No more treatment options were planned. Low dose corticosteroids were continued and azathioprine and pyridostigmine were prescribed. During follow-ups, symptoms were fully controlled. J Neurol Res. 2021;000(000):000-000 doi: https://doi.org/10.14740/jnr625