A myxoma is a neoplasm comprised of mesenchymal connective tissue. Myxomas of the upper extremity, and particularly of the hand, are rare. We present a case of a hypothenar myxoma causing ulnar neuropathy in a patient with a history of acute inflammatory demyelinating process. Treatment and management of myxoma may vary depending on whether the process is malignant or benign; thus, histologic diagnosis is critical to determining treatment. The purpose of this article is to review the pathophysiology and clinical features of myxomas, and to provide recommendations for evaluating and treating individuals with extremity masses of unclear clinical diagnosis.