Acquired myasthenia gravis

Diagnosis and treatment of myasthenia gravis

OBJECTIVE

To describe the clinical presentation, diagnosis, and treatment of myasthenia gravis (MG) while emphasizing the important role of the pharmacist.

DATA SOURCES

English-language articles from MEDLINE pertinent to MG study selection and data extraction: All relevant publications addressing MG management were considered, including prospective comparative trials, epidemiological studies, guideline statements, review articles, and editorials. Particular focus occurred on primary literature published after 1976, but limited amount(s) existed. The American Autoimmune Related Diseases Association, Autoimmune Information Network, Inc., Myasthenia Gravis Foundation of America, Inc. (MGFA), National Institute of Neurological Disorders and Stroke, and National Organization for Rare Disorders.

DATA SYNTHESIS

MG is an autoimmune disorder involving the neuromuscular junction causing characteristic weakness in voluntary muscle groups. To determine appropriate pharmacotherapy, one must characterize the disease based on the degree of function and region of muscles affected. MGFA established a classification system of the disease in order to assess severity. Contemporary treatments include cholinesterase inhibitors, corticosteroids, immodulating/immunosuppressive therapy, intravenous immune globulin, plasmapheresis, and thymectomy. Because of the lack of double-blind, placebo-controlled, randomized clinical trials, treatments are less evidence-based than many other disease states. Clinicians should be aware of the different treatments and recognize the best treatment for the individual.

CONCLUSIONS

The diagnosis and treatment of MG is a therapeutic challenge. Pharmacists play an essential role in the care of these patients by avoiding drugs that exacerbate the disease, promoting optimal pharmacotherapy, monitoring pharmacotherapy, and ensuring compliance with prescribed medications.

Pediatric myasthenia gravis and velopharyngeal incompetence

OBJECTIVE

To determine the clinical course of velopharyngeal incompetence in children with myasthenia gravis (MG).

METHODS

A 30-year retrospective study was performed using the medical records of 538 children who presented with velopharyngeal inadequacy (VPI) to a tertiary care academic pediatric center. Children with velopharyngeal incompetence due to myasthenia gravis were identified and their clinical courses were reviewed.

RESULTS

Four children were identified with velopharyngeal incompetence associated with myasthenia gravis. All four children required intervention for improvement of speech intelligibility. A speech prosthesis was the uniform intervention.

CONCLUSION

Neonatal myasthenia gravis patients should be followed long-term as symptoms may recur as speech impairment. In addition, a high index of suspicion for this entity is required for early diagnosis due to the highly variable presentation and clinical course.

Future Therapeutic Strategies in Autoimmune Myasthenia Gravis

Antibodies against muscle acetylcholine receptor (AChR) undoubtedly play a critical role in the pathology of most myasthenia gravis (MG) cases. Selective elimination of the majority of these antibodies should result in a considerable improvement of the MG symptoms. Such a specific elimination could be achieved by AChR-based immunoadsorbents. However, sufficient quantities of native human AChR are not available while bacterially expressed recombinant domains of the AChR are unable to bind satisfactorily MG antibodies. We have undertaken the production of the extracellular domains of human AChR subunits in eukaryotic systems, in native-like conformation, for their use as potent immunoadsorbents. The N-terminal extracellular domain (amino acids 1-210; alpha(1-210)) of the alpha(1) subunit of the human muscle AChR was expressed in the yeast Pichia pastoris. The polypeptide was water-soluble, glycosylated, and in monomer form. The alpha(1-210) bound 125I-alpha-bungarotoxin (125I-alpha-BTX) with a high affinity (Kd = 5.1 +/- 2.4 nM), and this binding was blocked by unlabeled d-tubocurarine and gallamine. Several conformation-dependent anti-AChR antibodies were able to bind alpha(1-210) as did antibodies from a large proportion of MG patients. The purified protein was subsequently immobilized on Sepharose-CNBr and was used to immunoadsorb anti-AChR antibodies from 64 MG sera. It eliminated more than 50% (50-94%) of the anti-AChR antibodies in 20% of the sera, whereas from another 30% of the sera it eliminated 20-60% of their anti-AChR antibodies. Work is in progress for the expression of the extracellular domain of all other muscle AChR subunits. It is expected that their combined use may eliminate the great majority of the anti-AChR antibodies from most MG patients.

Double trouble

A 78-year-old woman presented with vertical double vision. The Bielschowsky-Parks' three-step test suggested a left inferior rectus muscle paresis. Diagnostic testing confirmed the diagnosis of myasthenia gravis. Despite treatment with pyridostigmine bromide (mestinon) the diplopia persisted. She refused corticosteroid treatment and sought a second opinion, resulting in three unsuccessful strabismus surgeries to correct her ocular misalignment. The evaluation and management of ocular myasthenia gravis is reviewed and the appropriate timing of strabismus surgery is discussed.

Use of intravenous pulsed cyclophosphamide in severe, generalized myasthenia gravis

Twenty-three myasthenia gravis (MG) subjects, mean (SD) age 41.6 years (14), showing poor disease control or steroid-related side effects, received treatment for 12 months with intravenous cyclophosphamide (CP; n = 12) or placebo (PL; n = 11) in a randomized, double-blind trial. Pulses were given monthly at an initial dose of 500 mg/m(2) of body surface, and titrated according to changes of peripheral muscle strength or side effects. Changes of muscle strength, steroid and pyridostigmine requirements, and development of ventilatory failure or swallowing impairment were evaluated at 0, 3, 6, and 12 months. No differences were observed between groups at baseline. Statistically significant reductions of methylprednisone doses were noted in both groups but were more pronounced in subjects receiving CP than PL at 6 months (P < 0.05) and at 12 months (P < 0.03). At 12 months, five subjects on CP had tapered off their steroids whereas no subject on PL achieved further reductions (P < 0.03). Four CP subjects were not receiving steroids 36 months after completing the study and three other CP subjects had stopped pyridostigmine. CP improved muscle strength at 3 and 6 months, and this reached statistical significance compared to PL at 12 months mainly in the bulbar and masticatory (P < 0.009) and extraocular muscles (P < 0.03). Ventilatory failure was noted in one subject on CP (due to bronchopneumonia) and two on PL (due to muscle weakness). No significant increases of CP-related side effects were observed. Thus, this study suggests that intravenous pulses of CP allow reductions of systemic steroids usage without muscle strength deterioration or CP-related side effects.

Tensilon and the diagnosis of myasthenia gravis: are we using the Tensilon test too much?

BACKGROUND

Tensilon (edrophonium chloride) is a reversible acetylcholinesterase inhibitor used in the diagnosis of myasthenia gravis, diagnosis and treatment of arrhythmias, detection of early digitalis toxicity, reversal of neuromuscular blockade, and other medical conditions. Toxicity associated with Tensilon use has appeared in the literature for decades.

REVIEW SUMMARY

This review discusses the risks of Tensilon and the information practitioners should know before administering the drug. We review the literature regarding serious toxicity of this drug and offer recommendations for its safe use.

CONCLUSIONS

A careful medication history should be taken before the administration of Tensilon. Additionally, physicians should be aware of appropriate alternative methods of diagnosis before choosing to administer Tensilon. Physicians should be aware of the clinical situations where the Tensilon test no longer is indicated.

Current neuro-ophthalmic therapies

The clinical characteristics, differential diagnosis, and treatment options are presented for five different categories of neuro-ophthalmic disease. Nystagmus, optic neuritis, diplopia, pseudotumor cerebri, and temporal arteritis, are frequently encountered in neuro-ophthalmic practice. This article focuses on current therapies for these neuro-ophthalmic disorders. Potential differences in approach to pediatric versus adult patients are emphasized.

Plasmapheresis by using secondary membrane filters: twelve years of experience

Over 1,600 plasmapheresis procedures have been performed by using secondary on-line membrane plasma filters in 62 patients over the past 12 years in our institution. The disease categories treated include cryoprotein induced diseases such as cryoglobulinemia, immune mediated disorders, and familial type II-A hypercholesterolemia (FHC). Depending upon the molecular size of the offending agent, we used plasma filters (PF) with different pore sizes ranging from 0.02 microm to 0.04 microm or the cryoglobulin filter (CF) with an average pore size of 4.3 microm to remove cryoprecipitable proteins. One plasma volume was processed in each treatment. The results of treating 25 patient in over 550 procedures by using PF show it is safe and effective in treating immune mediated disorders and FHC. PF selectively removes macromolecules according to pore size and are more specific for the treatment of immune mediated diseases and FHC than plasma exchange. The results of treating 37 patients in over 1,100 procedures by using CF show it is safe and effective in selectively removing cryoproteins, and it is very specific for the treatment of cryoprotein induced diseases. Both PF and CF are biocompatible, with no complement activation. Unlike plasma exchange, secondary membrane plasma filters do not cause deficiency syndromes and do not require albumin or fresh frozen plasma as replacement fluid, making them more cost effective than plasma exchange.