methimazole and Myasthenia-Gravis

Acquired myasthenia gravis (AMG) is increasingly recognized in cats, yet information regarding the natural history of the disease, treatment, and outcome including occurrence of immune and spontaneous remission remains limited.. To determine the long-term outcome of cats with AMG without evidence of a cranial mediastinal mass (CMM).. Eight cats diagnosed with AMG without evidence of a CMM.. Retrospective case series. The medical records of cats diagnosed with AMG between 2005 and 2018 from 2 veterinary referral hospitals were reviewed for inclusion. Inclusion criteria consisted of a diagnosis of AMG, thoracic imaging, serum biochemistry including measurement of creatine kinase, and a CBC. Exclusion criteria were the presence of an identifiable CMM, or administration of methimazole or carbimazole.. All cats had an excellent long-term outcome, achieving immune remission within 6 months of diagnosis, including 4 cats that did not receive any treatment and whose natural course of disease involved spontaneous remission. Clinical presentation was heterogeneous, and skeletal muscle weakness and fatigability induced or exacerbated by the wheelbarrow exercise stress test were the most consistent abnormalities associated with AMG.. Cats diagnosed with AMG without evidence a CMM have a favorable outcome and frequently achieve immune remission. Moreover, the natural history of AMG in cats includes spontaneous remission when there is no evidence of a CMM. Attempting to rule out the presence of a CMM therefore refines prognosis, and treatment is not always necessary in this disease population.

Topics: Animals; Antithyroid Agents; Carbimazole; Cat Diseases; Cats; Female; Male; Methimazole; Myasthenia Gravis; Remission, Spontaneous; Retrospective Studies

Topics: Adolescent; Antithyroid Agents; Blepharoptosis; Cholinesterase Inhibitors; Drug Therapy, Combination; Exophthalmos; Graves Ophthalmopathy; Humans; Male; Methimazole; Myasthenia Gravis; Pyridostigmine Bromide; Thyrotropin; Thyroxine; Tomography, X-Ray Computed; Triiodothyronine

A 12-year-old female neutered ragdoll crossbred cat was presented for investigation of generalised weakness and regurgitation. The cat was being treated with transdermal methimazole for hyper-thyroidism, which had been diagnosed 10 weeks previously. An acetylcholine receptor antibody titre was consistent with acquired myasthenia gravis. Withdrawal of methimazole and treatment with pyridostigmine was followed by resolution of clinical signs and reduction of the acetylcholine -receptor antibody titre. Medical control of hyperthyroidism was subsequently achieved with carbimazole, administered in conjunction with pyridostigmine, and no recurrence of clinical signs was observed. Myasthenia gravis is an uncommon but clinically significant adverse effect of methimazole therapy in cats, and may be caused by immunomodulatory properties of this drug. An adverse drug reaction should be considered in cats receiving methimazole that develop myasthenia gravis, and potentially also other immune-mediated disorders.

Topics: Animals; Antithyroid Agents; Carbimazole; Cat Diseases; Cats; Female; Hyperthyroidism; Methimazole; Myasthenia Gravis; Pyridostigmine Bromide; Receptors, Cholinergic

Myasthenia gravis and Graves' disease are two autoimmune diseases with a similar mechanism, both having circulating organ autoantibodies and cell specific autoantibodies. It is not unusual for these diseases to occur together. There is a large body of data proving that antithyroid drugs such as methimazole and propylthiouracil have an immunomodulatory effect in addition to their thyrosuppressant action. This case report describes a 34-year-old woman hospitalized for just diagnosed myasthenic crisis (Osserman IV). She had a prior history of hyperthyroidism and treatment with methimazole was initiated. However, improvement in thyroid disease led to the burst of myasthenia. The phenomenon described as worsening of one disease while improving the other, the so-called 'see-saw' relationship, occurred in this case. The question is whether antithyroid drugs improve hyperthyroidism while unveiling or worsening myasthenia. Is the 'see-saw' relationship actually a therapeutic side effect of antithyroid drug? The proposed mechanism of methimazole action is intracellular: it lowers the level of proliferating cell nuclear antigen (PCNA). PCNA promotes selective apoptosis in some T lymphocyte clones. In this way, CD4+CD25+ regulatory T cells might 'skip' immune self-tolerance and autoantibodies against acetylcholine receptor may occur. Do antithyroid drugs actually create an immune 'thymic surrounding'?

Topics: Adult; Antithyroid Agents; Female; Humans; Methimazole; Myasthenia Gravis

Myasthenia gravis (MG) is an acquired autoimmune disorder causing skeletal muscle fatigue and weakness. This is a report of one woman and her daughter presenting with myasthenia and gravis and Grave's disease. It highlights possible hereditary component of this condition which has not been commonly reported in our setting.

Topics: Adult; Antithyroid Agents; Autoimmune Diseases; Cholinesterase Inhibitors; Female; Graves Disease; Humans; Methimazole; Middle Aged; Myasthenia Gravis; Pyridostigmine Bromide; Thyroid Diseases

A 41-year-old man with progressive limb weakness manifested fluctuating muscle weakness as seen in myasthenia gravis (MG). Laboratory investigations revealed hyperthyroidism without the complication of MG. Electrophysiological studies demonstrated abnormal features of neuromuscular transmissions resembling those of the Lambert-Eaton myasthenic syndrome rather than those of MG. A CT scan showed a mediastinal mass that suggested thymic hyperplasia which often complicates MG or hyperthyroidism. Medical treatment of hyperthyroidism resulted in resolution of MG-like symptoms and regression of thymic hyperplasia on CT concomitant with normalization of thyroid function. This case highlights the fact that careful investigations are needed to differentiate MG-like symptoms from genuine MG in cases of hyperthyroidism with thymic lesions.

Topics: Adult; Antithyroid Agents; Diagnosis, Differential; Graves Disease; Humans; Male; Methimazole; Muscle Weakness; Myasthenia Gravis; Thymus Hyperplasia; Thyrotoxicosis

We previously showed that myasthenia gravis (MG) has a mild clinical expression when associated with autoimmune thyroid diseases (AITD). In the present study we have investigated the frequency of thyroid-associated ophthalmopathy (TAO) in patients with Graves' disease (GD) associated with MG as compared with GD patients without MG. A total of 418 patients with GD were studied, 31 with MG and 387 without MG. TAO was evaluated by physical examination, exophthalmometry, computerized tomography, and computerized visual fields assessment. The overall prevalence of TAO was similar in GD patients with MG (61.2%) and in those without MG (56.4%). When the analysis was restricted to GD patients with ocular MG, a greater frequency of TAO was found (84.6%), compared with GD patients without MG or with GD patients with generalized MG, although the differences did not reach the statistical significance. GD patients with MG had a significantly greater prevalence (12.9%) of euthyroid ophthalmopathy (clinically overt ophthalmopathy without previous and/or current hyperthyroidism) than those without MG (3.1%; p = 0.003). The results suggest a preferential association between the ocular manifestations of GD and MG, which may be due to immunological cross-reactivity against common autoimmune targets in the eye muscle as well as to a common genetic background.

Topics: Adult; Antithyroid Agents; Female; Graves Disease; Humans; Iodine Radioisotopes; Male; Methimazole; Middle Aged; Myasthenia Gravis; Thyroidectomy; Thyroxine; Tomography, X-Ray Computed; Visual Fields

Diagnostic confusion between thyroid disease and myasthenia gravis (MG) can arise because the two may have similar clinical features, and also because of the more frequent coexistence of these autoimmune disorders in the same individual. In MG, autoantibodies directed against the acetylcholine receptor result in muscle weakness. Thymic pathology is well recognized in MG, with thymic hyperplasia frequent in early onset MG and thymoma more common in later onset MG. In Graves' disease, autoantibodies against thyroid antigens result in hyperthyroidism. A seldom-recognized feature of Grave's disease is the occurrence of an enlarged thymus (thymic hyperplasia) on chest CT, or of thymic lymphoid hyperplasia pathologically.. This report describes a case in which the discovery of a mediastinal mass during imaging of the thyroid, and the presence of myasthenic-like symptoms, in a patient with Graves' disease prompted investigations into whether the patient also had MG.. Despite symptoms which strongly suggested MG, subsequent investigations did not confirm the diagnosis, and treatment of Grave's lead to a resolution of the symptoms and regression of the thymic enlargement seen on CT.. The case study highlighted clinical similarities between Grave's disease and myasthenia gravis which might cause diagnostic confusion, and also the investigations which are useful in order to differentiate the two diseases. In addition to common clinical features, the autoimmune diseases Grave's disease and myasthenia gravis may both produce radiological thymic enlargement.

Topics: Adult; Anti-Anxiety Agents; Anti-Inflammatory Agents; Antithyroid Agents; Diagnosis, Differential; Female; Graves Disease; Humans; Methimazole; Myasthenia Gravis; Prednisone; Propranolol; Radiography; Thymus Hyperplasia; Thyrotropin; Thyroxine

Topics: Adolescent; Adult; Child; Female; Humans; Hyperthyroidism; Methimazole; Middle Aged; Myasthenia Gravis; Preoperative Care; Thymectomy