Introduction
Myasthenia Gravis (MG) is a rare neurological condition with a prevalence of 0.2 - 0.4 per thousand [1]. It is characterized by muscle weakness that worsens after use. In most patients, initial symptoms involve the extrinsic ocular muscles (EOMs). The symptoms progress to other bulbar muscles and limb muscles, resulting in generalized MG. In 10% of the patients, symptoms remain limited to the EOMs, known as ocular MG [2]. Antibodies to the acetylcholine receptor (AChR) are found in 85% of patients with generalized MG and 50% of those with ocular MG [3]. The antigenic target defines the subtypes of autoimmune MG. The most common target of autoantibodies in MG is the nicotinic acetylcholine receptor (AChR) in approximately 85% of the patients, followed by muscle-specific kinase (MuSK) and lipoprotein receptor-related protein 4 (LRP4) in about 15% [4].
Myeloproliferative Neoplasms (MPNs) are disorders due to stem-cell hyperplasia characterized by an increased peripheral blood cell count, overactive bone marrow, and proliferation of mature hematopoietic cells [5]. 2016 WHO category of MPNs includes the three major subcategories of Janus kinase 2 (JAK2)/ calreticulin (CALR)/ myeloproliferative leukemia virus oncogene (MPL) mutation-related MPNs: Polycythemia Vera (PV), Essential Thrombocythemia (ET), and Primary Myelofibrosis (PMF), as well as four other clinic-pathologic entities: chronic myeloid leukemia (CML), chronic neutrophilic leukemia (CNL), chronic eosinophilic leukemia, not otherwise specified (CEL-NOS) and MPN, unclassifiable (MPN-U) [6]. PMF includes pre-fibrotic/early PMF (pre-PMF) as well [7]. The diagnostic hallmark of CML is the invariable presence of the BCR-ABL1 mutation [6, 8, 9]. Characteristic bone marrow morphology is required for WHO compliant diagnosis, especially in distinguishing ET from pre-fibrotic PMF and masked PV [10].
Paraneoplastic neurological syndromes (PNS) are disorders associated with cancer, not caused by direct invasion, metastasis, or treatment consequences. They are autoimmune, rare, but potentially treatable [10] and can occur before or after primary cancer diagnosis [11]. The prevalence of these disorders varies with the type of cancer. PNS occurs in 2–3% of the patients with neuroblastoma or small cell lung carcinoma (SCLC) and 30–50% of the patients with thymoma. Overall, 0.5–1% of all patients with cancer have clinically disabling PNS [10]. PNS are more commonly associated with solid organ malignancies and very rarely with hematological malignancies. Hematological malignancies, including myeloproliferative disorders, are more commonly associated with dermatological paraneoplastic syndromes such as erythroderma, leukocytoclastic vasculitis, and sweet syndrome; and rheumatological paraneoplastic syndromes such paraneoplastic pemphigus and polymyalgia rheumatica [12]. Sweet syndrome is an acute febrile neutrophilic dermatosis characterized by Acute onset of tender, erythematous nodules, papules, plaques, or pustules on extremities, face, or upper trunk along with fever, malaise, and neutrophilia. Approximately 20% of patients with Sweet syndrome have underlying hematologic malignancy [13]. In this review, we have tried to identify case reports in which there is an association between MG and MPN. These cases have been compared and contrasted to evaluate whether MG can occur as a PNS in patients with underlying MPN.