A close look at autoimmune muscle disorders: association of Lambert–Eaton myasthenic syndrome with dermatomyositis

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

Introduction: Myasthenia gravis disease (MGD) and inflammatory myopathy (IM) are commonly reported in the literature and usually appear with thymic pathology. Lambert-Eton myasthenic syndrome (LEMS) associated with IM is extremely rare. Case Presentation: We report a 42-year-old female patient who presented with proximal muscle weakness of the upper and lower limbs, normal creatinine kinase (CK) level, and positive acetylcholine and voltage-gated calcium channel receptor antibodies. There were no oculobulbar symptoms and no history of thymoma, and the electrophysiological tests were unremarkable. Muscle biopsy revealed focal perimysial and perivascular inflammation, predominantly B-cell lymphocytes, in a non-necrotizing muscle. Conclusions: LEMS associated with IM, particularly B-cell inflammation, has never been reported in the absence of cancer history. Clinical investigations and myopathological features can help establish the diagnosis.

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.

Trouble at the junction: When myopathy and myasthenia overlap

Although myopathies and neuromuscular junction disorders are typically distinct, their coexistence has been reported in several inherited and acquired conditions. Affected individuals have variable clinical phenotypes but typically display both a decrement on repetitive nerve stimulation and myopathic findings on muscle biopsy. Inherited causes include myopathies related to mutations in BIN1, DES, DNM2, GMPPB, MTM1, or PLEC and congenital myasthenic syndromes due to mutations in ALG2, ALG14, COL13A1, DOK7, DPAGT1, or GFPT1. Additionally, a decrement due to muscle fiber inexcitability is observed in certain myotonic disorders. The identification of a defect of neuromuscular transmission in an inherited myopathy may assist in establishing a molecular diagnosis and in selecting patients who would benefit from pharmacological correction of this defect. Acquired cases meanwhile stem from the co-occurrence of myasthenia gravis or Lambert-Eaton myasthenic syndrome with an immune-mediated myopathy, which may be due to paraneoplastic disorders or exposure to immune checkpoint inhibitors.

Restrictive cardiomyopathy in dermatomyositis

The association between dermatomyositis and restrictive cardiomyopathy has not been reported before. We present here the clinical, echocardiographic and muscle biopsy data for a patient with dermatomyositis and restrictive cardiomyopathy. In a 78-year-old male with a history of arterial hypertension, recurrent episodes of atrial fibrillation and syncopes, rupture of an infra-renal aortic aneurysm with complications (recurrent QT-prolongation, lumbo-sacral plexopathy, transient ischaemic attack, peripheral embolism), monoclonal gammopathy, subdural haematoma, focal seizures, megaloblastic anaemia, leucopenia, eosinophilia, elevated muscle enzymes and increasing tiredness, dermatomyositis was diagnosed upon clinical presentation, muscle enzyme and muscle biopsy findings. Cardiological examination revealed atrial fibrillation, left anterior hemiblock and restrictive cardiomyopathy. After the exclusion of various differentials for restrictive cardiomyopathy, a causative relationship between restrictive cardiomyopathy and dermatomyositis was assumed. This case suggests the need for suspecting restrictive cardiomyopathy in patients with dermatomyositis. Patients with dermatomyositis should undergo a comprehensive cardiological investigation as soon as the neurological diagnosis is established.