Extremely Rare Case of Sclerosing Thymoma Type a With Neuroendocrine/Paraneoplastic Features of Isaac Merten Syndrome

Abstract

Sclerosing thymoma is an extremely rare neoplasm with only 16 reported [documented] cases worldwide in literature till date. The patient in our case presented with Sclerosing thymoma WHO Type A as well as clinical findings suggestive of Isaac's-Merten's syndrome (Neuromyotonia). CASE PRESENTATION: The Patient is a 53-year-old Caucasian male former smoker who presented with worsening dyspnea on exertion, and productive cough onset two weeks prior to presentation. He also complained of unintentional weight loss, generalized weakness, and progressively worsening bilateral hand contractures over the last year. On physical examination, the patient was noted to have contracted fingers on both hands with impaired flexion and extension. CXR and CT chest findings were consistent with pneumonia and an incidental large anterior 11.1 cm and 8.4 cm necrotic mediastinal mass that enveloped the main pulmonary artery. CT guided biopsy was performed and the mass was found to be of thymic origin. Neoadjuvant chemotherapy and radiation therapy were administered outpatient for tumor shrinkage prior to resection. The patient later underwent complete thymectomy and wedge resection of the left lung upper lobe. Pathology and immunohistochemistry results confirmed definitive diagnosis of sclerosing thymoma WHO Type A pattern. DISCUSSION: Sclerosing thymoma is an extremely rare type of thymoma accounting for <1% of all thymomas with preoperative clinical presentations that are widely varied. Kuo reported the first two cases of sclerosing thymoma in 1994. The WHO histologic classification of thymomas in 2004 entails 5 subtypes A, A1, B1, B2 and B3. These main subtypes are distinguished from the other rare variants of thymoma (sclerosing, micronodular, metaplastic, microscopic and lipofibroadenoma). Till date, only 16 cases of this sclerosing variant have been reported in literature worldwide. Although previously considered benign, even low-grade thymomas with type A pattern are considered malignant per International Thymic Malignancy Interest Group (ITMIG) guidelines. Certain paraneoplastic syndromes including the Isaac's-Merten's syndrome (Neuromyotonia) have been reported in association with thymomas on literature review. Neuromyotonia also known as peripheral nerve hyperexcitability is characterized by muscle stiffness as evidenced by bilateral hand contractures in our patient. CONCLUSIONS: Thymomas are rare mediastinal tumors. Sclerosing thymoma WHO type A is a very rare variant with few cases reported. Careful follow up of patients with thymic tumors is recommended to detect any local recurrence or distant metastasis.