Myasthenia gravis, corticosteroids, anticholinesterases

Myasthenic crisis: guidelines for prevention and treatment

Management of myasthenic crisis (MC) requires admission of the patient into a neurological intensive care unit and timely institution of an efficient and safe treatment. Despite the growing clinical experience with disease modifying immunotherapy there is no clinical consensus regarding the use of plasma exchange or high dose immunoglobulin treatment in an ICU setting. The choice of treatment modalities seem to rely mostly on institutional preferences primarily due to a lack of well-designed clinical trials comparing currently available therapeutic options. In our experience and based on a review of recent literature we advocate the use of plasma exchange (PE) as a primary modality in the acute care setting, supported by other immunomodulatory medications such as corticosteroids. Pharmacological management cannot substitute for adequate intensive care management of the respiratory and bulbar insufficiency associated with MC. Every effort should be done to prevent myasthenic exacerbation/crisis and to develop a maintenance management that leads to effective prevention.

[An unusual association: polymyositis, myasthenia gravis and thymoma]

Based on the inexistence of references in Brazilian and International literature of the association polymyositis, myasthenia gravis and thymoma in a young male adult, the authors propose to describe one case presenting the associated syndrome. The disease began when the patient was 22 years old, being the climax of its clinical expression four years later. It is emphasized the difficulty on the differential diagnosis between polymyositis and myasthenia gravis, once these diseases frequently have their clinical manifestations well individualized. In this study we call attention to the existence of clinical aspects of myasthenia gravis in patients presenting polymyositis and, on the other hand, histopathological alterations typical of polymyositis in myasthenic muscles, what makes the clinical diagnosis uncertain many times.

Acquired immune-mediated myasthenia gravis in a cat

Acquired myasthenia gravis was diagnosed in a four‐year‐old castrated male Somali in which the presenting signs consisted of progressive lameness, weakness, generalised muscle tremors, an inability to blink and voice loss. Clinical testing with edrophonium chloride, electrophysiology, immunocytochemistry and serum immunological techniques confirmed the diagnosis of myasthenia gravis and proved its immune‐mediated nature. Clinical remission was achieved following long term immunosuppression with corticosteroids.

Prolonged neuromuscular blockade with atracurium

During general anaesthesia with oxygen, nitrous oxide and enflurane, a 29-year-old woman received a total of 105 mg (1.78 mg X k-1) of atracurium over a 2.5 hour period. The neuromuscular blockade could not be completely reversed with neostigmine and mechanical ventilatory support was necessary for three hours postoperatively. The patient received succinylcholine without unusual sequelae before and after this episode. This is the first report of a patient who exhibited prolonged weakness after receiving atracurium.

Immunosuppression with corticosteroids and thymectomy in myasthenia gravis: an evaluation of immediate and short term results in 20 patients

A comparative study was conducted on two groups of patients with the generalized severe form of myasthenia gravis. The first group of 20 patients received oral daily doses of 60-100 mg of prednisone prior to thymectomy. The control group of 20 were submitted to surgery without prior corticosteroid treatment. The study included statistical analysis of the clinical results and surgical complications for both groups. The authors concluded that the use of steroids preoperatively is beneficial.

The in vivo effects of corticosteroids on thymocyte subsets in myasthenia gravis

The in vivo effects of corticotherapy on thymocyte subpopulations have been evaluated in patients with myasthenia gravis (MG). Ten patients receiving high-dose, long-term treatment were studied and compared with two control groups (MG untreated patients and normal age-matched subjects). In the treated group, the thymus was generally involuted; the percentage of OKT6+ or OKT4+T8+ thymocytes was profoundly decreased compared to controls. A significant percentage of OKT10 - cells was detected particularly among older patients, suggesting steroid-induced immigration. Conversely the percentage of more mature OKT3+ cells was increased. The balance between OKT4+T8- and OKT4-T8+ cells was unchanged in young patients (less than 40 years old) and increased in the older group. These data show that, as in the mouse, corticosteroids profoundly alter human thymocyte subsets.

Splenic and total-body irradiation treatment of myasthenia gravis

X-irradiation is introduced as a new therapeutic technique in the treatment of otherwise intractable myasthenia gravis (MG) and polymyositis (PM), on the basis that these dysimmune diseases are "lymphocyte dyscrasias" and that lymphocytes are the circulating cells most sensitive to x-irradiation. Splenic irradiation, 1000 rads per two-week course, repeated up to three courses, in five MG patients produced objective improvement in three and subjective improvement in another. The improvement was transient and accompanied by a temporary lymphocytopoenia. Total Body Irradiation (TBI), 150 rads over five weeks, in one polymyositis patient was followed by remarkable improvement, sustained and still increasing now after one year, associated with a sustained lymphocytopoenia. One MG patient has had definite improvement, maintained to the present, seven months after TBI, associated with persistent lymphocytopoenia. We suggest TBI may also be a treatment applicable to other types of dysimmune (autoimmune) diseases.

The relationship of plasma levels of pyridostigmine to clinical effect in patients with myasthenia gravis

The relationship between plasma levels of pyridostigmine to clinical evaluation of muscle power was examined in nine patients with myasthenia gravis during treatment with pyridostigmine in doses of 60 to 1040 mg daily. Five of the nine subjects demonstrated a trend towards a positive correlation, but in only two of them was this statistically significant at p < 0.05. In addition, the presence or absence of a possible correlation between muscle power and plasma concentration was not related to the duration of the disease, additional prednisolone therapy or thymectomy.

Identification of human thymic epithelial cells with antibodies to thymosin alpha 1 in myasthenia gravis

Thymosin-alpha 1 (alpha 1) is a potent thymic polypeptide hormone. Using anti-alpha 1 antibodies, we applied indirect immunofluorescence to human normal thymus of different ages and to hyperplastic, thymomatous, and "involuted" thymus of myasthenia gravis (MG) patients. Alpha 1 was localized only in the epithelial cells, lying singly, grouped, in Hassell's corpuscles, and proliferated in thymomas. Whereas normal thymuses and fewer and weakly stained cells, MG thymuses had many strongly positive epithelial cells; this was more evident in thymomas. Germinal centers were unstained. "Involuted" MG thymuses had small islands of brightly stained cells lying among the fatty tissue. In cultured thymuses from three MG patients, epithelial cells but not fibroblasts were brightly stained for alpha 1. Our findings (a) demonstrate the location, and presumably the origin, of alpha 1 to be the thymic epithelial cell; (b) suggest the possibility that excess alpha 1, because of its known effect on T-lymphocyte maturation and transformation of precursors to helper T-cells, may act pathologically to facilitate and perpetuate the dysimmune mechanism in MG; (c) may partially explain the beneficial effect of thymectomy in MG patients of any age; and (d) indicate that epithelial cells may be autonomous for the production of alpha 1 as evidenced by their alpha 1 positivity in culture.

Myasthenia gravis: signs, symptoms, diagnosis, immunology, and current therapy

Myasthenia gravis is a neuromuscular disease that presents clinically as fluctuating weakness of one or more skeletal muscle groups. Weakness becomes more severe with exercise and improves with rest. The disease is caused by an autoimmune reaction at or near the post-synaptic nicotinic acetylcholine receptor. The results of this immune reaction are the lytic destruction of the post-synaptic membrane and a reduction in the number of acetylcholine receptors. Myasthenia gravis can be diagnosed by repetitive exercise of the involved muscles, administration of edrophonium (Tensilon), electrophysiologic testing, or demonstration of anti-acetylcholine receptor antibodies. When the myasthenic weakness is mild or limited to the extraocular muscles, it may be treated with acetylcholinesterase inhibitors. When the weakness is more severe and/or more generalized, immunotherapy is most often indicated. Prednisone or prednisone plus thymectomy is the most frequently used form of immunotherapy. Azathioprine, 6-mercaptopurine, plasmapheresis, or gamma globulin injections are other immunotherapeutic options that may be useful in selected patients. A large number of drugs may precipitate or exacerbate myasthenic weakness.

Immunocytochemical localization of thymosin-alpha 1 in thymic epithelial cells of normal and myasthenia gravis patients and in thymic cultures

Thymosin alpha 1 (alpha 1) is a potent thymic polypeptide hormone. With antibodies against synthetic thymosin alpha 1, indirect immunofluorescence was applied to human normal thymus and to hyperplastic, thymomatous or "involuted" thymus of myasthenia gravis (MG) patients. Alpha 1 was localized only in the epithelial cells, lying singly, grouped, in Hassall's corpuscles or proliferated in thymomas. In contrast to normal thymus, which had fewer and more weakly stained cells, MG hyperplastic thymus had many strongly positive epithelial cells: this was markedly evident in thymomas. "Involuted" MG thymus had a few but brightly stained cells lying within the fatty tissue. In tissue cultures of human thymus, anti-alpha 1 stained the epithelial cells, but not fibroblasts. These findings: (a) demonstrate the origin of the thymic hormone alpha 1 to be the thymic epithelial cell; (b) raise the possibility that excess alpha 1 may act pathologically to facilitate and perpetuate the dysimmune mechanism in MG; (c) may partially explain the beneficial effect of thymectomy in MG patients of any age; and (d) suggest that epithelial cells may be autonomous for the production of alpha 1 as evidenced by their positivity in tissue culture.

Treatment of myasthenia gravis. Report on 139 patients

In the treatment of myasthenia gravis (MG) considerable progress has recently been achieved. Our experience is based on the observation of 139 patients with an average follow-up of 3 years and 4 months. A treatment plan and results are presented. Indications for thymectomy: all cases of MG in adult life, apart from ocular myasthenia without radiological thymoma and without electrophysiological and pharmacological signs of generalization; before puberty only cases with radiological thymoma and severely incapacitating or life-threatening signs. Median sternotomy is preferable for thymoma, the transcervical approach with a sternal split for non-neoplastic thymus. Mediastinal radiotherapy is indicated after removal of an invasive or adhesive thymoma. Indications for corticosteroids: 1) before thymectomy: respiratory weakness; 2) soon after thymectomy: life-threatening signs; 3) later after thymectomy: incapacitating or life-threatening signs; 4) as an alternative to thymectomy: when surgery cannot be performed or it is not indicated. Oral Prednisone was nearly always preferred: alternate-day high single dose (75 to 115 mg) has given good results in most cases even if in some cases a small dose was required in the "off day"; inversely a lower alternate-day or daily dose was often sufficient. Long-term results: following this schedule for adult patients good results were scored in 67% of thymomas, in 94% of hyperplasias, and in 62% of unthymectomized patients: in prepuberal life the few cases of severe MG have all shown a favorable evolution.

The effect of prednisolone on neuromuscular transmission in the rat diaphragm

Prednisolone, in concentrations of 0.004--0.032 mmol/l, increased the amplitude of the miniature end-plate potentials (MEPPs). A maximum increase to 134% of the control values was seen at 0.016 mmol/l. At higher prednisolone concentrations the MEPP amplitude gradually decreased to reach 77% of the control value at 0.62 mmol/l. The MEPP frequency was increased to twice the control value at 0.62 mmol/l. The quantal content of the end-plate potential (EPP), however, was not influenced by prednisolone. The response to iontophoretically applied acetylcholine was diminished, especially at 0.62 mmol/l prednisolone. Prednisolone, therefore, caused presynaptic effects as was shown by an increase in unitary MEPP amplitude and by a considerable number of giant MEPPs, which at increasing prednisolone concentrations was antagonized increasingly by a postsynaptic depressant effect. These results also provide an explanation for the adverse effects of prednisolone on the end-plate potential and on neuromuscular transmission.

Short-term effects of prednisolone on neuromuscular transmission in normal rats and those with experimental autoimmune myasthenia gravis

Electrophysiological investigations of the effects of bath-applied prednisolone at the neuromuscular junction were performed in muscles from normal rats and rats with experimental autoimmune myasthenia gravis (EAMG). In muscles from both groups, prednisolone reversible and significantly depressed the amplitudes of minature end-plate potentials (MEPPs), end-plate potentials (EPPs) and indirectly elicited action potentials (APs) without affecting resting membrane potentials. Prednisolone also caused a significant reduction in EPP rise time to peak and half-decay time while markedly increasing MEPP frequency and AP rise time to peak and duration. These effects were shown to be dose-dependent. The percentage decrease in amplitude after prednisolone perfusion was similar for EPPs and MEPPs, indicating that the depressive effect of prednisolone at the junction is postsynaptic. In all of the parameters studied, the percentage effect of prednisolone was the same in EAMG and normal preparations. No stimulus-linked repetitive EPPs or APs were observed after prednisolone. It is concluded that prednisolone has a depressive effect on neuromuscular transmission, but that this occurs only at high concentrations of the drug which are not achieved during the treatment of myasthenia gravis.

Myasthenia gravis: review of diagnosis and management

Although the cause of myasthenia gravis is still unknown, its pathogenesis appears clear: immunologic attack on synaptic receptors in muscle causes receptor deficiency, decreased miniature endplate potentials, and decrements in the compound action potentials evoked from muscles on repetitive stimulation of peripheral nerves. In addition to the involvement of skeletal muscle, some MG patients may manifest subtle alterations of the function of heart, lung, smooth muscle, and CNS, indicating that this is truly a systemic disorder. Modern therapy involves adjusting treatment to the needs of individual patients. Anticholinesterases, calcium, ephedrine, potassium, and germine partially correct the defect in neuromuscular transmission; prednisone, ACTH, cytotoxic drugs, antilymphocyte serums, gamma globulin, thoracic duct drainage, plasmapheresis, and thymectomy partially modify the abnormalities of the immune system.

Effect of prednisolone on motor end-plate fine structure: a morphometric study in hamsters

The fine structure of quadriceps motor end-plates in hamsters was analyzed quantitatively one, two, four, seven, and thirty-two weeks following intraperitoneal injections of prednisolone. Except for transient increases in postsynaptic length and membrane profile concentration after prednisolone administration at dosages of 4 mgper kilogram of body weight for one week and 2 mg per kilogram for four weeks, mean values for various measurable profiles in the presynaptic and postsynaptic regions showed no significant differences between control and treated animals.