Non-paraneoplastic Lambert-Eaton myasthenic syndrome: a brief review of 10 cases

Autonomic dysfunction detected by skin sympathetic response in Lambert-Eaton myasthenic syndrome: a case report

Background

Lambert-Eaton myasthenic syndrome (LEMS) is a type of paraneoplastic syndrome that may initially manifest itself with proximal weakness and gait abnormalities. Approximately up to 50% of LEMS patients have a primary autonomic dysfunction.

Case presentation

We present here a case of a 75-year-old male with symmetric proximal muscle weakness, dry mouth and constipation. The cutaneous response to scratch and upright tilt-table testing were positive. A repetitive nerve stimulation test showed that there was a decremental response of compound muscle action potential (CMAP) amplitude at 3 Hz while an incremental response at 20 Hz. The presence of antibodies against voltage-gated calcium channels (VGCC) confirmed the diagnosis. Because of the prominent symptom of autonomic disorder, the patient further underwent the test of skin sympathetic response (SSR). Lower amplitude and longer response duration were found in palms, while it evoked no response in soles.

Conclusions

In this case, we present the detailed results of SSR test on a patient suffering LEMS with autonomic disorder. Since autonomic dysfunction has a significant impact on clinical management and SSR test is an effective detection method, we recommend that SSR test be performed on patients with LEMS regularly.

Lambert-Eaton Myasthenic Syndrome

Lambert-Eaton myasthenic syndrome is a paraneoplastic or primary autoimmune neuromuscular junction disorder characterized by proximal weakness, autonomic dysfunction and ariflexia. The characteristic symptoms are thought to be caused by antibodies generated against the P/Q-type voltage-gated calcium channels present on presynaptic nerve terminals and by diminished release of acetylcholine. More than half of Lambert-Eaton myasthenic syndrome cases are associated with small cell lung carcinoma. Diagnosis is confirmed by serologic testing and electrophysiologic studies. 3,4-diaminopyridine is effective symptomatic treatment of LEMS.

Autoimmune Channelopathies at Neuromuscular Junction

The neuromuscular junction, also called myoneural junction, is a site of chemical communication between a nerve fiber and a muscle cell. There are many types of channels at neuromuscular junction that play indispensable roles in neuromuscular signal transmission, such as voltage-gated calcium channels and voltage-gated potassium channels on presynaptic membrane, and acetylcholine receptors on post-synaptic membrane. Over the last two decades, our understanding of the role that autoantibodies play in neuromuscular junction disorders has been greatly improved. Antibodies against these channels cause a heterogeneous group of diseases, such as Lambert-Eaton syndrome, Isaacs' syndrome and myasthenia gravis. Lambert-Eaton syndrome is characterized by late onset of fatigue, skeletal muscle weakness, and autonomic symptoms. Patients with Isaacs' syndrome demonstrate muscle cramps and fasciculation. Myasthenia gravis is the most common autoimmune neuromuscular junction channelopathy characterized by fluctuation of muscle weakness. All these disorders have a high risk of tumor. Although these channelopathies share some common features, they differ for clinical features, antibodies profile, neurophysiological features, and treatments. The purpose of this review is to give a comprehensive insight on recent advances in autoimmune channelopathies at the neuromuscular junction.

Five years experience on 3,4-diaminopyridine phosphate in Lambert-Eaton syndrome: Case reports

RATIONALE

To report our experience on 7 patients (4 males and 3 females), affected by nonparaneoplastic Lambert-Eaton myasthenic syndrome, treated with 3,4-diaminopyridine phosphate (3,4-DAPP) either alone or in combination with other immunosuppressants or steroids.

PATIENT CONCERNS

Patients have been evaluated at specific timepoints (ie, baseline and last 5 year follow-up), with neurological examination, autoantibodies against presynaptic voltage-gated Cav2.1 (P/Q type) calcium ion channel (VGCC) dosage, neurophysiological evaluation focusing on the increased amplitude of the compound muscle action potential (cMAP) after maximum voluntary effort, quantitative myasthenia gravis (QMG) and activities of daily living scales, and autonomic nervous system involvement evaluation.

OUTCOMES

Five out of 7 patients presented a clinical improvement persisting at last 5-year follow-up; 2 out of them improved taking only 3,4-DAPP at the maximal dosage, whereas the remaining received concomitant medications, such as prednisone and azathioprine. However, the clinical amelioration was not statistically significant. No one of the patients reported severe adverse events, except one, complaining of transient chin and perioral paresthesias. A significant association between QMG and the type of pharmacological drugs therapy (P = .028) emerged. Indeed, we observed an improvement of the clinical condition in all 3 subjects treated with 3,4-DAPP and prednisone.

CONCLUSIONS

In this study, we confirm 3,4-DAPP treatment efficacy on muscle strength, but minor evidence of drug effectiveness have been demonstrated on the autonomic nervous system involvement and on the deep tendon reflexes reappearance, a part from patients who received 3,4-DAPP associated to prednisone.

Long-term follow-up in infantile-onset lambert-eaton myasthenic syndrome

Lambert-Eaton myasthenic syndrome is a neuromuscular junction disorder characterized by proximal limb muscle weakness, fatigability, decreased deep-tendon reflexes, and autonomic symptoms. There are 2 forms of Lambert-Eaton myasthenic syndrome: one most frequently associated with small-cell lung cancer (P-Lambert-Eaton myasthenic syndrome) and the other that is a pure autoimmune form (NP-Lambert-Eaton myasthenic syndrome). Lambert-Eaton myasthenic syndrome is a very rare disorder in children younger than age 12 years. Herein, we report a 25-year-old man with NP-Lambert-Eaton myasthenic syndrome, which onset was at the age of 10 years. To date, this is the most long-term follow-up of NP-Lambert-Eaton myasthenic syndrome in childhood. In our patient, the only symptomatic treatment with 3,4-diaminopyridine phosphate has been sufficient to guarantee him a good quality of life. Our data remind physicians to keep in mind the diagnosis of Lambert-Eaton myasthenic syndrome in children with a proximal myopathic pattern and they confirm the specificity of compound muscle action potential incremental pattern after brief maximal effort in Lambert-Eaton myasthenic syndrome.

Lambert-Eaton myasthenic syndrome and solitary cerebellar metastasis in a patient with occult small-cell lung cancer: a rare experience

The authors describe a case of 60-year-old male patient presented with a 6 month history of progressive weakness of all the four limbs, ataxia, droopy eyelids and bulbar features. Further laboratory and electrodiagnostic studies confirmed the diagnosis of Lambert-Eaton myasthenic syndrome (LEMS). MRI of the brain showed a cerebellar tumour which, following surgery was revealed to be a metastatic small-cell lung carcinoma. Paraneoplastic LEMS together with solitary cerebellar metastasis was diagnosed but no evidence of primary malignancy was detected. An extensive search for related malignancies failed to get any clue. The patient underwent a total surgical excision of tumour and the histopathology revealed a metastatic small cell carcinoma. This case highlights that rarely both paraneoplastic LEMS and cerebellar mass can precede the primary malignancy causing them.

Lambert-Eaton myasthenic syndrome: from clinical characteristics to therapeutic strategies

Lambert-Eaton myasthenic syndrome (LEMS) is a neuromuscular autoimmune disease that has served as a model for autoimmunity and tumour immunology. In LEMS, the characteristic muscle weakness is thought to be caused by pathogenic autoantibodies directed against voltage-gated calcium channels (VGCC) present on the presynaptic nerve terminal. Half of patients with LEMS have an associated tumour, small-cell lung carcinoma (SCLC), which also expresses functional VGCC. Knowledge of this association led to the discovery of a wide range of paraneoplastic and non-tumour-related neurological disorders of the peripheral and central nervous systems. Detailed clinical studies have improved our diagnostic skills and knowledge of the pathophysiological mechanisms and association of LEMS with SCLC, and have helped with the development of a protocol for early tumour detection.

Lambert-eaton myasthenic syndrome; pathogenesis, diagnosis, and therapy

Lambert-Eaton Myasthenic Syndrome (LEMS) is a rare disease with a well-characterized pathogenesis. In 50% of the patients, LEMS is a paraneoplastic manifestation and caused by a small cell lung carcinoma (SCLC). Both LEMS patients with SCLC and those without this tumour have in 85% of cases pathogenetic antibodies of very high LEMS specificity against voltage-gated calcium channels (VGCCs) in the cell membrane of the presynaptic motor nerve terminal. Better understanding of LEMS pathogenesis has lead to targeted symptomatic therapy aimed at the neuromuscular junction and to semispecific immuno-suppression. For SCLC LEMS, tumour therapy is essential.