Successful alternate day guanidine therapy following guanidine-induced neutropenia in the Lambert-Eaton myasthenic syndrome

Lambert-Eaton myasthenic syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune disease characterized by proximal muscle weakness, loss of tendon reflexes, and autonomic dysfunction. Muscle weakness usually starts in the upper legs and can progress to oculobulbar and in severe cases respiratory muscles. P/Q-type voltage-gated calcium channels (VGCCs) localized in the presynaptic motor nerve terminal and in the autonomic nervous system are targeted by antibodies in LEMS patients. These antibodies can be detected in about 90% of patients, and the presence of decrement and increment upon repetitive nerve stimulation is also a highly sensitive diagnostic test. Rapid diagnosis is important because of the association with SCLC in 50%-60% of patients, which stresses the need for vigorous tumor screening after diagnosis. Clinical parameters can predict tumor probability and guide frequency of tumor screening. Treatment of the tumor as well as symptomatic treatment and immunosuppression can effectively control symptoms in the majority of patients.

Autoimmune paraneoplastic syndromes associated to lung cancer: A systematic review of the literature Part 4: Neurological paraneoplastic syndromes, involving the peripheral nervous system and the neuromuscular junction and muscles

The development of new immune treatment in oncology and particularly for lung cancer may induce new complications, particularly activation or reactivation of auto-immune diseases. In this context, a systematic review on the auto-immune paraneoplastic syndromes that can complicate lung cancer appears useful. This article is the fourth of a series of five and deals mainly with neurological paraneoplastic syndromes involving the peripheral nervous system and the neuromuscular junction and muscles.

Screening for small-cell lung cancer: a follow-up study of patients with Lambert-Eaton myasthenic syndrome

PURPOSE

A small-cell lung carcinoma (SCLC) is found in 50% of patients with Lambert-Eaton myasthenic syndrome (LEMS). We evaluated screening to optimize screening strategy for SCLC. It is important to detect these tumors early in newly diagnosed patients with LEMS to offer optimal patient treatment.

PATIENTS AND METHODS

A large nationwide cohort study of consecutive patients in the Netherlands, seen between 1990 and 2007, were screened for the presence of a tumor using chest x-ray, computed tomography of the thorax (CT-thorax), [(18)F]fluorodeoxyglucose positron emission tomography (FDG-PET), bronchoscopy, and/or mediastinoscopy.

RESULTS

SCLC was found in 54 patients, and in 46 patients, no tumor was found during a median follow-up of 8 years (range, 3 to 26 years). All patients with SCLC had a positive smoking history and 86% were still smoking at diagnosis. SCLC was found in 92% of these patients within 3 months and in 96% within a year. At first screening, CT-thorax detected an SCLC in 45 patients (83%), whereas chest x-ray found the tumor in only 23 patients (51%). An SCLC was found during secondary screening in another nine patients (median, 3 months; range, 1 to 41 months). In six patients, a lung tumor was found by CT-thorax or FDG-PET, and in three patients, extrapulmonary metastases were found, initially without identifiable tumor mass on CT-thorax.

CONCLUSION

In almost all patients (96%), the SCLC was found within 1 year of diagnosis. CT-thorax scans detected most of the tumors (93%) and was far more sensitive than chest x-ray (51%). FDG-PET may have additive value in selected cases. We propose a screening protocol based on CT-thorax and FDG-PET.

Available treatment options for the management of Lambert-Eaton myasthenic syndrome

Lambert-Eaton myasthenic syndrome is a rare, but reasonably well-understood, antibody-mediated autoimmune disease that is caused by serum auto-antibodies and results in muscle weakness and autonomic dysfunction. One half of the patients have an idiopathic form, the other half a tumour-associated form of the disease. Three randomised trials and a large number of smaller clinical studies have resulted in a number of drugs becoming available for the treatment of Lambert-Eaton myasthenic syndrome. Several drugs are available for the symptomatic treatment of the disease, including guanidine, aminopyridines or acetylcholinesterase inhibitors. Other therapies aim to deplete the serum autoantibodies or to suppress the immune system. For this purpose, immunomodulating strategies, such as intravenous immunoglobulins or plasmapheresis, or several immunosuppressive agents are available. Chemotherapy has successfully ameliorated the course of disease in Lambert-Eaton myasthenic syndrome patients with an underlying tumour.

The effects of presynaptic calcium channel modulation by roscovitine on transmitter release at the adult frog neuromuscular junction

Calcium (Ca2+) influx through presynaptic calcium channels triggers transmitter release, and any alterations in the gating of these calcium channels results in changes in the magnitude of transmitter released. We used (R)-roscovitine, a cyclin-dependent kinase inhibitor that also appears to act directly on calcium channels, as a tool to modulate presynaptic calcium influx and study effects on transmitter release. We show that this compound increased the quantal content of acetylcholine released from the Rana frog motor nerve terminal (by 149%) without changing paired-pulse facilitation (under low calcium conditions). In contrast, exposure to 3,4-diaminopyridine (DAP; which similarly affects transmitter release by partially blocking potassium channels, altering the shape of the presynaptic action potential, and indirectly increasing calcium entry) increased paired-pulse facilitation (by 23%). In addition, we show that (R)-roscovitine predominately slowed deactivation kinetics of calcium current (by 427%) recorded from Xenopus frog motoneurons, and as a result, increased the integral of calcium channel current evoked by a physiological action potential waveform (by 44%). Because we did not observe any significant effects of structurally related cyclin-dependent kinase inhibitors [(S)-roscovitine or olomoucine] on evoked transmitter release or calcium current kinetics, it appears that these effects of (R)-roscovitine are independent of cyclin-dependent kinases (cdks). In summary, we hypothesize that (R)-roscovitine effects on transmitter release at the adult frog neuromuscular junction (NMJ) are mediated by its effects on calcium channel gating, and these effects increase our understanding of calcium triggered secretion at this synapse.

Low-dose guanidine and pyridostigmine: relatively safe and effective long-term symptomatic therapy in Lambert-Eaton myasthenic syndrome

Guanidine hydrochloride is known to be highly effective in the symptomatic treatment of the Lambert-Eaton myasthenic syndrome (LEMS). However, because of its potentially dangerous side reactions of hematologic abnormalities and renal insufficiency, 3,4-diaminopyridine, which is not readily available in the United States, is recommended as the preferred drug for LEMS. We used low-dose guanidine and pyridostigmine combination therapy in 9 patients with LEMS and analyzed its long-term safety and effectiveness. In all patients, a liberal amount of pyridostigmine was used, while daily guanidine dose was kept below 1000 mg a day, and guanidine was given between pyridostigmine dosings. This combination therapy was used for 3-102 months (mean: 34.1 months) and improved clinical status in all patients. Although guanidine had to be discontinued due to severe gastrointestinal symptoms in 3 cases, no serious side reactions such as bone marrow suppressions or signs of renal insufficiency developed in any case. Thus, we conclude that low-dose guanidine therapy is relatively safe and effective for long-term symptomatic treatment of LEMS when it is combined with pyridostigmine.

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.