A neuromuscular transmission disorder: combined myasthenia gravis and Lambert Eaton syndrome in one patient

Myasthenia gravis Lambert-Eaton overlap syndrome

INTRODUCTION

To assess whether a myasthenia gravis (MG) Lambert-Eaton overlap syndrome (MLOS) exists.

METHODS

Case reports that met the universally accepted diagnostic criteria for MG and Lambert-Eaton myasthenic syndrome (LEMS) were sought through a PubMed search. Fifty-five possible cases of MLOS were identified.

RESULTS

Thirty-nine cases met the diagnostic criteria for MG and LEMS. Analysis of clinical features showed that these patients have common MG and LEMS symptoms: oculo-bulbar paresis and good response to anti-cholinesterase for MG and limb weakness and decreased or absent reflexes for LEMS. All had the classical LEMS pattern in the repetitive nerve stimulation test: low compound muscle action potential amplitude and incremental response > 60% with brief exercise or at high rate of stimulation. Eight patients had combined positive acetylcholine receptor antibody (AChR-ab) or muscle-specific kinase-ab and voltage-gated calcium channel- ab tests.

CONCLUSIONS

A myasthenia gravis Lambert-Eaton overlap syndrome (MLOS) does exist.

A case of lambert-eaton myasthenic syndrome with small-cell lung cancer and transient increase in anti-acetylcholine-receptor-binding antibody titer

BACKGROUND

Lambert-Eaton myasthenic syndrome (LEMS) is a presynaptic neuromuscular junction disorder that is most frequently associated with small-cell lung cancer (SCLC). The titers of antibodies against voltage-gated calcium channels are frequently increased in LEMS, but only rarely is titer of anti-acetylcholine-receptor-binding antibodies (AChR-abs) increased.

CASE REPORT

A 57-year-old male was admitted to our hospital due to dry mouth and eyes and progressive proximal limb weakness of 2 months duration. The results of a repetitive nerve stimulation test disclosed all criteria for the electrophysiological LEMS pattern, and the patient's AChR-abs titer was 0.587 nmol/L. At a follow-up performed 5 years after successful treatment of SCLC and LEMS, his AChR-abs titer had decreased to 0.001 nmol/L.

CONCLUSIONS

We suggest that this was a case of transient pseudopositivity of AChR-abs in SCLC with LEMS.

A patient with coexisting myasthenia gravis and lambert-eaton myasthenic syndrome

Background

The coexistence of myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome (LEMS) is very rare and remains controversial.

Case Report

A 48-year-old woman initially presented with noticeable right ptosis and intermittent diplopia. She then developed fluctuating proximal limb weakness and difficulty in swallowing. The serum titer of anti-acetylcholine-receptor antibody was elevated and the edrophonium (Tensilon) test was positive. However, repetitive nerve stimulation revealed abnormalities typical of LEMS. The patient exhibited a good response to treatment with anticholinesterase inhibitors and steroids, and long-term evaluation disclosed that she presented with the clinical, electrophysiological, and immunological characteristics of both diseases.

Conclusions

The reported clinical and electrophysiological features suggest that this patient was a very rare case of combined MG and LEMS.

A Diagnostic and Management Dilemma

BACKGROUND

Neuromuscular junction disorders are usually categorized as either presynaptic or postsynaptic. The most frequently encountered disorder of the postsynaptic neuromuscular junction is acquired myasthenia gravis. Lambert-Eaton myasthenic syndrome is a well-known prototype of the presynaptic autoimmune disorders of neuromuscular transmission. These major disorders of neuromuscular transmission are relatively common and distinctly recognized, but co-occurrence of these disorders (overlap myasthenic syndrome) is rare and has so far attracted little attention.

REVIEW SUMMARY

This report describes a patient with acquired myasthenia gravis and immunologic coexistence of Lambert-Eaton myasthenic syndrome (overlap myasthenic syndrome) in association with abdominal/uterine leiomyosarcoma. The patient presented with acute respiratory failure, making identification and management of her illness challenging. A general overview of the complexities associated with overlap between myasthenia gravis and Lambert-Eaton myasthenic syndrome is provided and this patient's complicated clinical course and response to therapy are discussed.

CONCLUSION

To our knowledge, this is the first report of overlap myasthenic syndrome in conjunction with abdominal leiomyosarcoma. The immunologic coexistence of acquired myasthenia gravis and Lambert-Eaton myasthenic syndrome in a patient with a malignant smooth-muscle tumor is intriguing and suggests that a common paraneoplastic process targeting 2 different onconeural antigens was the underlying pathogenic mechanism in this patient.

Peroneal nerve repetitive nerve stimulation test: its value in diagnosis of myasthenia gravis and Lambert-Eaton myasthenic syndrome

We have developed a repetitive nerve stimulation (RNS) technique for the peroneal nerve. Normal limits for the decremental responses for the anterior tibialis and extensor digitorum brevis muscles are 6-21% at the low rate of stimulation and 44-70% at the high rate of stimulation. These values exceed the normal limits for other commonly tested muscles. This may be due to the lower safety factor for neuromuscular transmission for the anterior tibialis and extensor digitorum brevis muscles. We present 4 cases in which the peroneal nerve RNS test was crucial for the diagnosis of the limb-girdle form of MG or LEMS. Thus, we conclude that, in a small number of patients with neuromuscular transmission disorders, the peroneal nerve RNS test is needed for confirmation of disease.

[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.

Immunological evidence for the co-existence of the Lambert-Eaton myasthenic syndrome and myasthenia gravis in two patients

Two patients are described in whom a clinical and electromyographic diagnosis of the Lambert-Eaton myasthenic syndrome (LEMS) was made. Serum antibodies to voltage-gated calcium channels (VGCCs), the antigenic target in LEMS and to acetylcholine receptors (AChRs), the antigen in myasthenia gravis, were detected at raised titres in both cases, using radioimmunoassays based on 125I-omega-Conotoxin labelled VGCCs and 125I-alpha-Bungarotoxin labelled AChRs. These data provide immunological evidence for the coexistence of the two disorders in these patients.

Edrophonium responsiveness not necessarily diagnostic of myasthenia gravis

Uneqivocally positive edrophonium tests, both clinically and electrophysiologically, were observed in a classic case of the Lambert-Eaton myasthenic syndrome. A review of the literature revealed that a positive edrophonium response has been reported in a majority of cases of myasthenia gravis (MG) and overlap myasthenic syndrome and in some cases of the Lambert-Eaton myasthenic syndrome, botulism, congenital myasthenic syndrome, drug-induced myasthenic syndrome, the Guillain-Barre syndrome, and amyotrophic lateral sclerosis. From this, we conclude that an unequivocally positive edrophonium test alone is not necessarily diagnostic of MG and that the diagnosis of MG should be based on the clinical features together with edrophonium-responsiveness and other laboratory findings.

A neuromuscular transmission disorder: combined myasthenia gravis and Lambert-Eaton syndrome in one patient

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