Lambert-Eaton myasthenic syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is an idiopathic or paraneoplastic syndrome producing antibodies against presynaptic voltage-gated P/Q calcium channels. This decreases calcium entry into the presynaptic terminal, which prevents binding of vesicles to the presynaptic membrane and acetylcholine release. LEMS is most often associated with small cell lung cancer, although idiopathic presentations comprise approximately 40% of the cases. The most common initial complaint is proximal muscle weakness involving the lower extremities more than the upper extremities. Depressed deep tendon reflexes and autonomic dysfunction are frequently present. Involvement of the bulbar or respiratory muscles is rare. Diagnosis is confirmed by electrophysiological testing, which demonstrates small compound muscle action potentials and facilitation with exercise or 20-Hz repetitive stimulation. A serum test for voltage-gated calcium channel antibodies is commercially available. Treatment involves removing the cancer associated with the disease. If cancer is not found, immunosuppressive medications and acetylcholinesterase inhibitors are used with moderate success. Patients with idiopathic LEMS should be screened every 6 months with chest imaging for cancer.     

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

This review of the Lambert-Eaton myasthenic syndrome (LEMS) emphasizes electrodiagnosis and includes a case report. A 50-year-old woman had become progressively weaker over 1.5 years. The suspected diagnosis was confirmed by the clinical electrophysiological findings and was made 6 months before the patient's oat-cell carcinoma was found. After treating with local radiation and chemotherapy, the myasthenic syndrome went into remission as the pulmonary lesion resolved.     

Lambert-Eaton myasthenic syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disease of the neuromuscular junction, and approximately 60% of patients with LEMS have a tumor, mostly small cell lung cancer (SCLC), as a paraneoplastic neurological syndrome. The clinical data of Japanese patients in the present study are as follows: the ratio of men to women is 3: 1 (mean age, 62 years; age range, 17-80 years). Of the patients with LEMS, 61% have SCLC, whereas the others do not have cancer. Clinical symptoms are usually characterized by proximal muscle weakness and dysautonomia. In less than 10% of the patients, there are signs of cerebellar dysfunctions (paraneoplastic cerebellar degeneration with LEMS; PCD-LEMS), and these are usually associated with SCLC. The diagnosis can be confirmed by detecting a specific antibody in a radioimmunoprecipitation assay and finding reduced amplitude of compound muscle action potential that increases by over 100% after maximum voluntary activation or 50Hz of nerve stimulation. The pathomechanism of LEMS is characterized by impaired transmission across the neuromuscular junction because of autoantibodies directed against the presynaptic P/Q-type voltage-gated calcium channels (P/Q-VGCCs). Histopathologic evaluation of the cerebellum in patients with PCD-LEMS showed a reduced number of P/Q-type VGCCs in the molecular layer. Therefore, it was hypothesized that P/Q-VGCC antibodies may induce cerebellar dysfunction after entering the CNS in patients with PCD-LEMS. Specific tumor therapy in patients with LEMS as well as cancer often improves the neurologic deficit. Tumor removal is the primary treatment for LEMS. If the result of the primary screening is negative, screening should be repeated after 3-6 months and thereafter every 6 months for up to 2 years. Most patients benefit from 3, 4-diaminopyridine administered with pyridostigmine. In those with severe weakness, intravenous gamma globulin (IVIg) or plasmapheresis confers short-term benefits. Prednisone when administered alone or in combination with immunosuppressive drugs can achieve long-term control of the disorder.     

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.     

Congenital Lambert-Eaton myasthenic syndrome.

A 4 year old girl had been hypotonic and areflexic since birth with delayed milestones in motor development. Repetitive stimulation at high rates performed at 3 years elicited an incremental response typical of the Lambert-Eaton Syndrome.     

Lambert-Eaton myasthenic syndrome in children

Lambert-Eaton myasthenic syndrome is a presynaptic disorder of neuromuscular transmission. It is characterized by muscle weakness, hyporeflexia, and autonomic dysfunction. It is most often associated with small cell carcinomas of the lung. Rare cases have been reported in children. We recently encountered two children with Lambert-Eaton myasthenic syndrome associated with antibodies to P/Q-type calcium channel but without evidence of neoplasms. Both patients showed prolonged and significant improvement following cyclosporin treatment. The diagnosis of Lambert-Eaton myasthenic syndrome should be considered in children with progressive weakness and a negative work-up for the usual causes. High-frequency repetitive nerve stimulation and P/Q-type calcium-channel antibodies may confirm the diagnosis.     

Autonomic dysfunction in Lambert-Eaton myasthenic syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder characterized by muscle wakness and autonomic dysfunction. Recentex vivo andin 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 logical assays andin vitro pharmacologic and electrophysilogical studies are also discussed. Funding for the author's research comes from grants from the National Health and Medical Research Council of Australia, Canberra, the Clive and Vera Ramaciotti Foundation, Sydney, and by an AMRAD (Melbourne) Postdoctoral Award.     

Recombinant calcium channel is recognized by Lambert-Eaton myasthenic syndrome antibodies

The authors studied sera from 36 patients with Lambert-Eaton myasthenic syndrome (LEMS) by immunoblots using the recombinant protein derived from the DNA sequence encoding for the domain III S5-S6 linker of the P/Q-type voltage-gated calcium channel al subunit. The results of 18 patients were positive for antibodies to this recombinant protein. The results of 2 of 10 patients with lung cancer without LEMS were also positive.     

Small cell lung cancer with Lambert-Eaton myasthenic syndrome

Four of 69 cases of small cell lung cancer (SCLC) showed evidence of Lambert-Eaton myasthenic Syndrome (LEMS) were studied neurologically and neurophysiologically in four years. The LEMS appearance were preceded that of SCLC in 3 cases for two years at most. Repeated stimulation of ulnar nerve examination showed diminished amplitude of initial response (0.2-0.9 mv); Amplitude of the response at 3 c/s stimulation for 3 sec was diminished 20-63%. (control 3% decreases-13% increases) but that at 20 c/s stimulation for 10 sec increased 200-800% increases. (control: 20% decreases-56% increases). These findings were important for diagnosis of LEMS. The abnormalities of neurotransmission seems to be due to inadequate release of acetyl choline from nerve terminals at abnormal active zone of Ca++ channels.     

Lambert-Eaton myasthenic syndrome presenting with severe respiratory failure

Two cases of Lambert-Eaton myasthenic syndrome (LEMS) who presented with primary respiratory failure are reported. In each case, although not initially suspected clinically, the electrophysiological findings, which included reduced compound muscle action potential amplitudes, decrement to 3-Hz stimulation, and potentiation after 40-Hz stimulation, led to the diagnosis in the critical care unit. Electrophysiological studies of the respiratory system, including repetitive nerve stimulation of the phrenic nerve, were extremely valuable in management. As shown by these cases, the severe respiratory failure in LEMS is reversible with treatment. Thus, LEMS should be considered in cases of unexplained respiratory failure, other clinical features of the disorder sought, and the electrophysiological hallmarks looked for, including studies of the respiratory system. © 1996 John Wiley & Sons, Inc.     

Postexercise facilitation of reflexes is not common in Lambert-Eaton myasthenic syndrome

Postexercise facilitation (PEF) with clinical reflexes, H-reflex, and T-reflexes at the ankle and knee was systematically studied in 16 patients with Lambert-Eaton myasthenic syndrome (LEMS). PEF was observed in ankle and knee deep tendon reflexes in five patients, in H-reflex in three patients, and in T-reflexes in six patients. When all reflex tests were combined, 7 (43.7%) of 16 patients showed PEF by at least one test. The authors conclude that the PEF of reflexes, the most helpful diagnostic clinical marker for LEMS, is not common.     

Decrement pattern in Lambert-Eaton myasthenic syndrome is different from myasthenia gravis

The decrement pattern at low rates of repetitive nerve stimulation in myasthenia gravis (MG) is characterized by a decrease of compound muscle action potential size within the first 4-5 responses. With subsequent stimuli, compound muscle action potential size either increases or does not change. Following an observation that the pattern of decrement might be different in patients with Lambert-Eaton myasthenic syndrome (LEMS), we retrospectively studied traces from eight LEMS patients and 14 patients with seropositive generalized MG, calculating decrement percent from first to fourth and from first to ninth compound muscle action potential. In the LEMS patients, compound muscle action potential amplitude decreased progressively from first to ninth stimulus at 2, 3 or 5Hz in all traces but one. In contrast, MG patients demonstrated the expected improvement after the initial decrement in all traces except one. In the evaluation of patients suspected of having myasthenia gravis, the finding of progressive decrement pattern at low rates of repetitive nerve stimulation may alert the electromyographer to the possibility of Lambert-Eaton syndrome and prompt the performance of further electrodiagnostic tests.     

Electrophysiological diagnostic criteria of Lambert-Eaton myasthenic syndrome

Various parameters of the repetitive nerve stimulation (RNS) test of the abductor digiti quinti muscle were analyzed statistically in 34 patients with Lambert-Eaton myasthenic syndrome (LEMS). The sensitivity and specificity of the increments after exercise and after 50-HZ stimulation for the diagnosis of LEMS were compared with reference values in 40 normal subjects and data from 538 tests in patients with myasthenia gravis (MG). When we used a 100% increment (the "gold standard") as the normal limit for the postexercise facilitation (PEF) or the high-rate stimulation (HRS) test, the diagnosis of LEMS was confirmed in 29 (85%) cases. When a 60% increment was used as the normal limit, the diagnosis of LEMS was made in 97% of cases. In MG, a 60% increment was observed in only 4 of 538 cases by HRS and in none by the exercise test. Thus, the use of a 60% increment showed a sensitivity of 97% for the diagnosis of LEMS and a specificity of 99% in excluding MG. A 60% increment in either the PEF or HRS test for the diagnosis of LEMS is a desirable alternative to the 100% increment previously considered to be the gold standard for this diagnosis.     

Transient Lambert-Eaton myasthenic syndrome associated with systemic lupus erythematosus

We present a patient who developed the Lambert-Eaton myasthenic syndrome (LEMS) in association with systemic lupus erythematosus (SLE). Severe proximal weakness with electrodiagnostic evidence of LEMS developed over 2 days during an exacerbation of cutaneous manifestations (bullous pemphigoid) associated with SLE. Following an increase in the daily dose of prednisone, there was complete clinical restitution of strength within 2 weeks and a slower resolution of electrodiagnostic abnormalities over 6 months. Marked serologic abnormalities were present at the onset and showed improvement over 6-8 months. LEMS had been infrequently described in association with SLE. The immunologic features of both SLE and LEMS suggest a linkage between the two diseases in this patient. We hypothesize that increased antibodies associated with exacerbation of SLE cross reacted with the neuromuscular junction membrane to produce LEMS.