Lambert–Eaton Myasthenic Syndrome and Dermatomyositis With Anti–TIF1-gamma Autoantibody: A Unique Association of Autoimmune Neuromuscular Conditions Without Malignancy

Abstract

Lambert–Eaton myasthenic syndrome (LEMS) is a presynaptic neuromuscular junction disorder, and dermatomyositis (DM) is an idiopathic inflammatory myopathy. LEMS and DM are uncommon conditions that can present similarly and are often associated with autoantibodies. Concomitant LEMS and DM have only been reported a few times, and most of those cases were paraneoplastic. We present the first reported case of a patient with antivoltage gated calcium channel antibody positive LEMS who subsequently developed DM with antitranscription intermediary factor 1-gamma (anti–TIF1-γ) antibodies. Interestingly, both conditions occurred without evidence of malignancy. This diagnosis of LEMS and DM with characteristic clinical, electrodiagnostic, and histopathological evidence led to a beneficial modification of the patient's therapeutic regimen. Due to the fact that overlapping concurrent neuromuscular conditions are rare, a high clinical suspicion is needed to identify, evaluate (including appropriate cancer screenings), and appropriately treat these patients.

Unusual Association of Non-paraneoplastic Variant of Lambert-Eaton Myasthenic Syndrome with Predominant B-cell Inflammatory Myopathy

“…Although 60% of patients with LEMS were paraneoplastic, only four reported cases were associated with IMs (DM/PM spectrum) (4-6, 8, 9). The non-paraneoplastic variant of LEMS-associated IMs is extremely rare, and the underlying mechanism is still unclear (7). Because no serological marker for the paraneoplastic variant of LEMS has been explored, the association with malignancy is currently difficult to establish.…”

“…The coexistence of MGD and IM is commonly reported in the literature and usually appears with thymic pathology (2,3). Lambert-Eton myasthenic syndrome, an isolated variant of MGD, is rarely reported with IM (1,(4)(5)(6)(7)(8). The whole three disorders are autoimmune in nature and can be associated with malignancies such as breast, colon, and ovarian cancers and Non-Hodgkin lymphomas (1).…”

“…The association of LEMS with IM is extremely rare. To our knowledge, seven cases in the literature have been reported since 1984 (1,(4)(5)(6)(7)(8). Dermatomyositis and polymyositis (DM/PM) with T-cell inflammation were the most common IM-associated variants.…”