Paraneoplastic cerebellar degeneration (PCD) is a rare neuroimmunological disease that may accompany tumors. In this article, we present a patient with progressive gait difficulty who was diagnosed with PCD and, in a rare comorbidity, with papillary thyroid carcinoma (PTC) following malignancy screening. A 46-year-old male patient reported having experienced poor balance for 2 years. A neurological examination revealed nystagmus, intention tremor, and ataxia, and anti-thyroid peroxidase and anti-thyroglobulin levels were found to be elevated. A brain MRI showed significant cerebellar atrophy in the superior vermis. Malignancy screening for PCD was performed, and thyroid ultrasonography revealed a nodule in the left lobe, while PET/CT detected elevated focal F-18 fluorodeoxyglucose uptake in the thyroid. Onconeuronal antibodies (anti-Hu, anti-Yo, anti-Ri, anti-amphiphysin, anti-Tr, anti-PPCA-2, anti-Ma, anti-CV-1, and anti-ANNA-3) were negative. Pathologic examination of the thyroid revealed PTC, for which the patient was treated with 0.4 g/kg intravenous immunoglobulin and referred to the medical oncology department. This case demonstrates that clinicians must be alert to the rare comorbidity of PCD and PTC.

中文翻译：

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副肿瘤性小脑变性的罕见共存：甲状腺乳头状癌

副肿瘤性小脑变性 (PCD) 是一种罕见的神经免疫疾病，可能伴随肿瘤发生。在本文中，我们介绍了一名患有进行性步态困难的患者，该患者被诊断为 PCD，并且在一种罕见的合并症中，在恶性肿瘤筛查后患有甲状腺乳头状癌 (PTC)。一名 46 岁男性患者报告称其平衡能力差 2 年。神经系统检查显示眼球震颤、意向性震颤和共济失调，抗甲状腺过氧化物酶和抗甲状腺球蛋白水平升高。脑部MRI显示上蚓部有明显的小脑萎缩。对 PCD 进行了恶性肿瘤筛查，甲状腺超声检查显示左叶有一个结节，而 PET/CT 检测到甲状腺局灶性 F-18 氟脱氧葡萄糖摄取升高。神经元抗体（抗 Hu、抗 Yo、抗Ri、抗amphiphysin、抗Tr、抗PPCA-2、抗Ma、抗CV-1和抗ANNA-3）均为阴性。甲状腺病理检查显示 PTC，为此患者接受了 0.4 g/kg 静脉注射免疫球蛋白治疗并转诊至肿瘤内科。该病例表明临床医生必须警惕 PCD 和 PTC 的罕见合并症。