Autonomic dysfunction in Lambert-Eaton myasthenic syndrome

Autonomic nervous system involvement in autoimmune encephalitis and paraneoplastic neurological syndromes

In autoimmune neurological diseases, the autonomic nervous system can be the primary target of autoimmunity (e.g. autoimmune autonomic ganglionopathy), or, more frequently, be damaged together with other areas of the nervous system (e.g. Guillain-Barré syndrome). Patients with autoimmune encephalitis and paraneoplastic neurological syndromes (PNS) often develop dysautonomia; however, the frequency and spectrum of autonomic signs and symptoms remain ill defined except for those scenarios in which dysautonomia is a core feature of the disease. Such is the case of Lambert-Eaton myasthenic syndrome, Morvan syndrome or anti-NMDAR encephalitis; in the latter, patients with dysautonomia have been reported to carry a more severe disease and to retain higher disability than those without autonomic dysfunction. Likewise, the presence of autonomic involvement indicates a higher risk of death due to neurological cause in patients with anti-Hu PNS. However, in anti-Hu and other PNS, as well as in the context of immune checkpoint inhibitors' toxicities, the characterization of autonomic involvement is frequently overshadowed by the severity of other neurological symptoms and signs. When evaluated with tests specific for autonomic function, patients with autoimmune encephalitis or PNS usually show a more widespread autonomic involvement than clinically suggested, which may reflect a potential gap of care when it comes to diagnosing dysautonomia. This review aims to revise the autonomic involvement in patients with autoimmune encephalitis and PNS, using for that purpose an antibody-based approach. We also discuss and provide general recommendations for the evaluation and management of dysautonomia in these patients.

Sudomotor Dysfunction

Disorders of sudomotor function are common and diverse in their presentations. Hyperhidrosis or hypohidrosis in generalized or regional neuroanatomical patterns can provide clues to neurologic localization and inform neurologic diagnosis. Conditions that impair sudomotor function include small fiber peripheral neuropathy, sudomotor neuropathy, myelopathy, α-synucleinopathies, autoimmune autonomic ganglionopathy, antibody-mediated hyperexcitability syndromes, and a host of medications. Particularly relevant to neurologic practice is the detection of postganglionic sudomotor deficits as a diagnostic marker of small fiber neuropathies. Extensive anhidrosis is important to recognize, as it not only correlates with symptoms of heat intolerance but may also place the patient at risk for heat stroke when under conditions of heat stress. Methods for assessing sudomotor dysfunction include the thermoregulatory sweat test, the quantitative sudomotor axon reflex test, silicone impressions, and the sympathetic skin response.

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.

Review of the Diagnostic Challenges of Lambert–Eaton Syndrome Revealed Through Three Case Reports

Lambert–Eaton syndrome (LES) is a rare immune-mediated disorder characterized by proximal leg weakness, autonomic symptoms and hypoactive tendon reflexes. The paraneoplastic form is associated with small-cell lung cancer in 50-60% of cases, whereas the remaining cases are found in younger adults with a higher likelihood of coexisting autoimmune disease. The early recognition of LES is crucial for improving clinical outcomes but remains a major challenge. In this review, we analyze the clinical characteristics and diagnostic considerations in treating LES through a series of three case studies, one of which showed definitive response to pyridostigmine and corticosteroid combination therapy, followed by spontaneous remission. Patients were assessed by image-based screening, serological testing and electrophysiological evaluations, which included respiratory and autonomic testing. A better understanding of the common pitfalls in the clinical, serological and neurophysiologic diagnosis of LES through assessment of typical LES dysfunction throughout the nervous system should enable improved recognition and treatment of this syndrome.

Autoimmune autonomic disorders

Autoimmune autonomic disorders occur because of an immune response directed against sympathetic, parasympathetic, and enteric ganglia, autonomic nerves, or central autonomic pathways. In general, peripheral autoimmune disorders manifest with either generalized or restricted autonomic failure, whereas central autoimmune disorders manifest primarily with autonomic hyperactivity. Some autonomic disorders are generalized, and others are limited in their anatomic extent, e.g., isolated gastrointestinal dysmotility. Historically, these disorders were poorly recognized, and thought to be neurodegenerative. Over the last 20 years a number of autoantibody biomarkers have been discovered that have enabled the identification of certain patients as having an autoimmune basis for either autonomic failure or hyperactivity. Peripheral autoimmune autonomic disorders include autoimmune autonomic ganglionopathy (AAG), paraneoplastic autonomic neuropathy, and acute autonomic and sensory neuropathy. AAG manifests with acute or subacute onset of generalized or selective autonomic failure. Antibody targeting the α3 subunit of the ganglionic-type nicotinic acetylcholine receptor (α3gAChR) is detected in approximately 50% of cases of AAG. Some other disorders are characterized immunologically by paraneoplastic antibodies with a high positive predictive value for cancer, such as antineuronal nuclear antibody, type 1 (ANNA-1: anti-Hu); others still are seronegative. Recognition of an autoimmune basis for autonomic disorders is important, as their manifestations are disabling, may reflect an underlying neoplasm, and have the potential to improve with a combination of symptomatic and immune therapies.

Paraneoplastic disorders of the central and peripheral nervous systems

Paraneoplatic neurologic syndromes (PNS) have been seminally defined as acute or subacute neurological syndromes resulting from nervous system dysfunction that is remote from the site of a malignant neoplasm or its metastases. However, in respect to our current understanding of their pathogenesis we may redefine these disorders as cancer-related dysimmune neurologic syndromes. We first deal with the epidemiology and the pathogenesis of PNS, then the different classic PNS are reviewed with clinical features according to the associated onconeuronal antibodies. Finally, therapeutic approaches are discussed.

Pupil abnormalities in selected autonomic neuropathies

Examination of the pupil provides an opportunity to detect disturbances in the autonomic innervation of the eye. The pupil is frequently affected in patients with generalized autonomic neuropathies. This literature review confirms a high prevalence of sympathetic deficits and parasympathetic deficits in acute or subacute dysautonomia, diabetes, amyloidosis, pure autonomic failure, paraneoplastic syndromes, Sjögren syndrome, familial dysautonomia, and dopamine beta-hydroxylase deficiency. It confirms the relative scarcity of a pupil abnormality in patients with multiple system atrophy. There are difficulties in clinical diagnosis of pupil abnormalities and interpretation of pupil pharmacologic tests, particularly when combined sympathetic and parasympathetic deficits are present.

Lambert-Eaton myasthenic syndrome

The Lambert-Eaton Myasthenic Syndrome (LEMS) is characterised by proximal muscle weakness initially affecting gait, autonomic symptoms (dry mouth, constipation, erectile failure), augmentation of strength during initial voluntary activation, and depressed tendon reflexes with post-tetanic potentiation. The disorder is paraneoplastic (small cell lung cancer) in about 60p. cent (P-LEMS); no cancer is associated in the remainder (NP-LEMS). LEMS affects all races. NP-LEMS can occur in childhood as well as adult life; P-LEMS is unusual at<30 Years. The weakness results from a reduction in the quantal release of acetylcholine from motor nerve terminals, caused by autoantibodies to P/Q-type voltage-gated calcium channels (VGCCs) that are provoked by tumour VGCCs in P-LEMS; the stimulus in NP-LEMS is not known. These antibodies may be implicated in the rarely associated cerebellar degeneration. The diagnosis can be confirmed by detecting the specific antibody in a radioimmunoprecipitation assay, and by finding a reduced compound muscle action potential amplitude that increases by>100p. cent following maximum voluntary activation. Most patients benefit from 3,4-diaminopyridine; pyridostigmine is less effective. Specific tumour therapy in P-LEMS will often ameliorate the neurological disorder. In those with severe weakness, IVIg or plasmapheresis confers short-term benefits. Prednisone alone or combined with azathioprine or cyclosporin can achieve long-term control of the disorder.

Lambert-Eaton Myasthenic Syndrome

A high index of suspicion is essential in arriving at the correct diagnosis of Lambert-Eaton myasthenic syndrome (LEMS). LEMS should be considered in the differential in any patient who has proximal weakness, reduced or absent muscle stretch reflexes, and dry mouth. Weakness predominates in hip and shoulder muscles, but may also affect ocular and oropharyngeal muscles to a lesser extent. The diagnosis is confirmed by demonstrating characteristic electromyographic findings-low-amplitude muscle responses that increase dramatically after activation. Most patients also have circulating antibodies to the voltage-gated calcium channel. Half the patients with LEMS have a malignancy, usually small-cell lung cancer. The diagnosis should trigger an intensive search for malignancy, especially in older patients with a history of smoking. Younger, nonsmoking patients are likely to have LEMS as part of a more general autoimmune state. Successful treatment of the underlying cancer leads to improvement in many patients. More than 85% of patients have clinically significant benefit from 3,4-diaminopyridine (DAP). In over half of these, the improvement is marked. If severe weakness persists despite DAP, immunotherapy should be considered. Plasma exchange and high-dose immunoglobulin induce transient improvement in many patients, but function rarely becomes normal. Combinations of prednisone, azathioprine, or cyclosporine have been used with variable success. Improvement, if any, occurs only after many months and requires chronic administration of immunosuppressive medications at significant doses. The long-term prognosis in LEMS is determined by the presence of cancer or other autoimmune disease.

Passive transfer of Lambert-Eaton syndrome to mice induces dihydropyridine sensitivity of neuromuscular transmission

Lambert-Eaton myasthenic syndrome (LEMS) is a paraneoplastic disorder in which autoantibodies apparently target the voltage-gated Ca2+ channels that regulate acetylcholine (ACh) release at motor nerve terminals. P/Q-type Ca2+ channels are primarily involved in ACh release at mammalian neuromuscular junctions. Passive transfer of LEMS to mice by repeated administration of plasma from LEMS patients reduces the amplitude of the perineurial P/Q-type current, and unmasks a dihydropyridine (DHP)-sensitive L-type Ca2+ current at the motor nerve terminal. The present study sought to determine if this DHP-sensitive component contributes to ACh release. Mice were treated for 30 days with plasma from healthy human controls or patients with LEMS. For some studies, diaphragms from naive mice were incubated with LEMS or control human plasma for 2 or 24 h. End-plate potentials (EPPs) and miniature end-plate potentials (MEPPs) were recorded from neuromuscular junctions in the hemidiaphragm. Treatment of mice with LEMS plasma evoked the characteristic electrophysiological signs of LEMS: reduced quantal content and facilitation of EPP amplitudes at high-frequency stimulation. Quantal content was also reduced in muscles incubated acutely with LEMS plasma. Nimodipine, a DHP-type blocker of L-type Ca2+ channels, did not significantly affect the quantal content of muscles treated for 2 or 24 h with either control or LEMS plasma, or following chronic treatment with control plasma. However, following 30 days treatment with LEMS plasma, nimodipine significantly reduced the remaining quantal content to 57.7 +/- 3.3 % of pre-nimodipine control levels. Thus, DHP-sensitive Ca2+ channels become involved in synaptic transmission at the mouse neuromuscular junction after chronic, but not acute treatment with LEMS plasma. However, reductions in quantal release of ACh occur even after very short periods of exposure to LEMS plasma. As such, development of the L-type Ca2+ channel contribution to ACh release during passive transfer of LEMS appears to occur only after quantal release is significantly impaired for an extended duration, suggesting that an adaptive response of the ACh release apparatus occurs in LEMS.

Remote neurologic manifestations of cancer

Paraneoplastic disorders may affect any part of the central or peripheral nervous systems. Although relatively uncommon, these disorders are a significant cause of neurologic morbidity for cancer patients. At least some paraneoplastic syndromes are believed to be caused by an autoimmune reaction against shared tumor-neural antigens. This article summarizes the clinical features of paraneoplastic disorders, the current evidence for autoimmunity, and guidelines for diagnosis and treatment.

Autonomic dysfunction in Lambert-Eaton myasthenic syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder characterized by muscle weakness and autonomic dysfunction. Recent ex vivo and in vitro studies demonstrate that autoantibodies to the P/Q-subtype of voltage-gated calcium channel inhibit transmitter release from parasympathetic, sympathetic, and enteric neurons, a mechanism likely to underlie the widespread autonomic dysfunction in LEMS. This review summarizes clinical studies characterizing the autonomic symptoms and signs in LEMS and the effectiveness of treatment in alleviating these symptoms. Serological assays and in vitro pharmacologic and electrophysiologic studies are also discussed.

Neurogenic bladder in Lambert-Eaton myasthenic syndrome and its response to 3,4-diaminopyridine

Autonomic dysfunction, as well as neuromuscular involvement, is a common manifestation of Lambert-Eaton myasthenic syndrome (LEMS). Dry mouth and impotence have been described as typical features of autonomic dysfunction, but neurogenic bladder is infrequent or subclinical in LEMS. We report a patient with neurogenic bladder secondary to LEMS whose condition responded to 3,4-diaminopyridine (3,4-DAP). In this patient's serum, results of repeated measurement with P/Q-type VGCC antibodies proved positive, but not with N-type VGCC and synaptotagmin antibodies. A review of the literature turned up a few patients with voiding dysfunction related to LEMS, but no urodynamic studies were done on these patients. Ours is the first case in which 3,4-DAP was efficacious in treating LEMS and neurogenic bladder. Responses of 3,4-DAP in urodynamic studies suggest that in this LEMS patient neurogenic bladder was caused by defective neurotransmission both in the autonomic detrusor and skeletal abdominal muscles.

Lambert-Eaton myasthenic syndrome with ophthalmoparesis and pseudoblepharospasm

We report a patient initially diagnosed as having ocular myasthenia gravis who showed progressive ophthalmoparesis and pseudoblepharospasm together with positive acetylcholine receptor antibodies. Repeated evaluation with high-frequency repetitive stimulation revealed an incremental response and elevated titers of antibodies against presynaptic calcium channels, confirming Lambert-Eaton myasthenic syndrome. Systemic evaluation revealed no malignant neoplasm but revealed euthyroid Hashimoto's disease. Immunomodulative therapy including plasma exchange and administration of an immunosuppressent (azathioprine) combined with a potassium-channel blocker (3,4-diaminopyridine) reduced the ocular abnormalities. We conclude that the ocular manifestations in this patient were probably caused by Lambert-Eaton myasthenic syndrome.

Lambert-Eaton myasthenic syndrome

The Lambert-Eaton myasthenic syndrome is a neuromuscular disorder characterised by defective neurotransmitter release at autonomic neurones and presynaptic terminals of the neuromuscular junction. It is caused by an IgG autoantibody formed against especially the P/Q type of voltage-gated calcium channels (VGCC) which is an essential component of the mechanism of neurotransmitter release. Many patients have an associated small cell carcinoma of the lung which appears to provide the antigenic stimulus for antibody production, although there is another group with no underlying malignancy. Both groups show an association with immunological disorders. Assay of VGCC antibody titres and electrophysiological tests help to differentiate Lambert-Eaton myasthenic syndrome from other disorders of the neuromuscular junction. Several drugs and therapeutic interventions capable of producing significant clinical improvement are currently available. Patients should also be investigated for underlying tumours, the specific treatment of which can result in remission or amelioration of symptoms.

Functional evaluation of inhibition of autonomic transmitter release by autoantibody from Lambert-Eaton myasthenic syndrome

The effects of the anti-voltage-gated Ca2+ channel (VGCC) antibody obtained from patients with Lambert-Eaton myasthenic syndrome (LEMS) on autonomic neurotransmission were studied in in-vitro experiments. The releases of acetylcholine (ACh) and norepinephrine from the autonomic nerves were evaluated by changes in the contractile responses of guinea pig taenia caeci and left atria to electric field stimulation, respectively. Incubations for 6 hours with LEMS serum and IgG, both of which contain anti-VGCC antibody, markedly suppressed the parasympathetic response but did not affect the sympathetic response. Pharmacological experiments with specific blockers to the VGCC subtypes showed that the Q-type VGCC is closely linked to the genesis of the parasympathetic response. We suggest that the anti-VGCC antibody from the LEMS patients specifically reduces the ACh release from the parasympathetic nerve by binding to the Q-type VGCC.

Effect of Lambert-Eaton myasthenic syndrome antibodies on autonomic neurons in the mouse

Somatic muscle weakness and autonomic symptoms characterize the autoimmune Lambert-Eaton myasthenic syndrome (LEMS). The former results from IgG autoantibody-mediated down-regulation of P/Q-type voltage-gated calcium channels at motor nerve terminals and consequent reduction in acetylcholine release; the basis for the autonomic symptoms is unknown. Using omega-conotoxins GVIA and MVIIC and omega-agatoxin IVA that block N-, Q-, and P-type channels, we investigated ex vivo the calcium channels subserving transmitter release from postganglionic parasympathetic neurons in the bladder and from postganglionic sympathetic neurons in the vas deferens of mice injected with IgG from LEMS patients or from controls. Calcium influx through N-, P-, and Q-type channels subserved transmitter release from parasympathetic and sympathetic neurons in control mice. In test mice, the component of transmitter release subserved by P-type channels was abolished by four of four LEMS IgG preparations, that subserved by Q-type channels was significantly reduced by three, and that subserved by N-type channels by one. Thus, LEMS IgG impairs transmitter release from parasympathetic and sympathetic neurons through down-regulation of one or more subtypes of voltage-gated calcium channels. The results suggest that antibody-mediated interference with specific ion channel function may also underlie autonomic dysfunction occurring in other autoimmune diseases.

Autonomic neuropathy, II: Specific peripheral neuropathies

Autonomic dysfunction is a common complication of peripheral neuropathies. It is often of little clinical importance, but some conditions may cause profound disturbance of autonomic function. These conditions include acute dysautonomia, diabetes, primary and familial amyloidosis, Guillain-Barré syndrome, porphyria, and some inherited neuropathies. A wide range of neuropathies are associated with lesser degrees of autonomic dysfunction. These include hereditary neuropathies, and neuropathies associated with metabolic disturbances, alcohol abuse, malignancy, medications, infections, and connective tissue disorders.

Neuromuscular disorders in systemic malignancy and its treatment

Neuromuscular dysfunction in patients with known or suspected malignancy has three basic etiologies: (1) a direct effect of the neoplasm, either by compression or infiltration; (2) a "remote," or paraneoplastic, effect of cancer; or (3) a side effect of anticancer treatment, radiation or chemotherapy. A variety of clinical features or syndromes are due to damage either at the level of the neuron (anterior horn cell or dorsal root ganglion neuron), nerve root(s), brachial or lumbosacral plexus, peripheral nerve (motor, sensory, and/or autonomic), neuromuscular junction, or muscle. A complex clinical picture evolves when dysfunction in due to more than one cause at more than one anatomical site.

Lambert-Eaton myasthenic syndrome: clinical diagnosis, immune-mediated mechanisms, and update on therapies

The Lambert-Eaton myasthenic syndrome (LEMS) is a rare condition in which weakness results from a presynaptic abnormality of acetylcholine release at the neuromuscular junction. It was first described as a paraneoplastic syndrome in patients with lung cancer but we now know about half of the patients with LEMS do not have cancer. The diagnosis is made on the basis of the clinical findings and characteristic electromyographic patterns. Recent evidence indicates that LEMS results from an autoimmune attack directed against the voltage-gated calcium channels on the presynaptic motor nerve terminal. In patients with LEMS who have cancer, effective treatment of the underlying tumor frequently produces marked improvement of weakness as well. Otherwise, treatment involves the use of agents that improve neuromuscular transmission by increasing the release of neurotransmitter, and immunosuppression.

[Lambert-Eaton syndrome and small cell cancer. Etiopathogenic considerations apropos of 2 cases]

The authors report two cases of Lambert-Eaton myasthenic syndrome associated with small cell lung carcinoma. Following the observations, the clinical diagnosis of this syndrome is considered. We discuss the autoimmune pathogenesis and the relation between paraneoplastic syndrome and small cell cancer. This syndrome is caused by autoantibodies that block the voltage-dependent calcium channels at motor nerve terminals. Small cell carcinoma cells appear to express calcium channels, suggesting that autoantibody production may be triggered by tumor calcium channels determinants. The autoimmune paraneoplastic syndrome theory refers to cross-antigenicity.

Deficiency of sympathetic nervous system function in myasthenia

The norepinephrine (NE) and epinephrine (E) responses to forearm ischemia were studied in 24 myasthenic patients and 22 subjects with lumbar disc disease (control group). In some of these myasthenic (11 cases) and control (11 cases) subjects the NE and E responses to orthostasis were also investigated. In controls both stimuli induced a rise in NE urinary excretion without significantly changing the E excretion. On the other hand, in myasthenic patients forearm ischemia and orthostasis were followed by an augmentation in E excretion, the NE excretion remaining unchanged or even undergoing a depression. In other myasthenic patients (10 cases) and subjects with lumbar disc disease (10 cases) NE and E responses to exercise were tested. The results were similar to those presented above: controls reacted to exercise by a rise in NE excretion, while myasthenic patients, by an augmentation in E excretion; the NE excretion underwent no change or even decreased after exercise in myasthenia. The obliteration of NE response to all three testing stimuli found in myasthenic patients may be considered as a sign of their sympathetic deficiency. In such patients the normal E discharge produced by forearm ischemia, orthostasis or exercise may be interpreted as a compensatory reaction, being probably the consequence of sympathetic deficiency. The noradrenergic deficit of myasthenic patients is ascribable to their cholinergic hyperactivity.

[Electrophysiologic data on myasthenic syndromes of the Lambert-Eaton type. A series of 23 cases]

The electrophysiological data of 23 adult patients with Lambert-Eaton myasthenic syndrome (LEMS) have been reviewed. Lung carcinoma was disclosed in 17. In six cases with an EMG follow-up ranging between one and 17 years no carcinoma was detected. The results of repetitive nerve stimulation test (RNS) were not statistically different between the 2 groups. Low CMAP ulnar amplitude was present in all patients (mean: 1.7 mV). Decremental response at low rate of stimulation (3 Hz) was present in 17/20 (means: 30%). An abnormal incremental response at high rate of stimulation was present in all cases (mean: 826%). The authors emphasize the interest of a 50 Hz stimulation for 4 s. Increase of the 'F-wave' amplitude was noticed in some cases. Electrophysiological changes suggestive of an associated mild neuropathy were noticed in eight patients but H-reflex was present in 3/3 cases. SFEMG abnormalities were found in 6/6 cases. In one case, stimulated SFEMG showed more blockings and an increased jitter with low rate of stimulation. In one case the electrical pattern of RNS could be misinterpreted as myasthenia gravis in one tested muscle only. The author's results suggest that CMAP amplitude and RNS test could be used to appreciate the short-term improvement of LEMS with treatment and in some cases for the long-term follow-up.