The pathophysiology of penicillamine-induced myasthenia gravis

Pathomechanisms and Clinical Implications of Myasthenic Syndromes Exacerbated and Induced by Medical Treatments

Myasthenic syndromes are typically characterized by muscle weakness and increased fatigability due to an impaired transmission at the neuromuscular junction (NMJ). Most cases are caused by acquired autoimmune conditions such as myasthenia gravis (MG), typically with antibodies against the acetylcholine receptor (AChR). Different drugs are among the major factors that may complicate pre-existing autoimmune myasthenic conditions by further impairing transmission at the NMJ. Some clinical observations are substantiated by experimental data, indicating that presynaptic, postsynaptic or more complex pathomechanisms at the NMJ may be involved, depending on the individual compound. Most robust data exist for the risks associated with some antibiotics (e.g., aminoglycosides, ketolides, fluoroquinolones) and cardiovascular medications (e.g., class Ia antiarrhythmics, beta blockers). Apart from primarily autoimmune-mediated disorders of the NMJ, de novo myasthenic manifestations may also be triggered by medical treatments that induce an autoimmune reaction. Most notably, there is growing evidence that the immune checkpoint inhibitors (ICI), a modern class of drugs to treat various malignancies, represent a relevant risk factor to develop severe and progressive medication-induced myasthenia via an immune-mediated mechanism. From a clinical perspective, it is of utmost importance for the treating physicians to be aware of such adverse treatment effects and their consequences. In this article, we aim to summarize existing evidence regarding the key molecular and immunological mechanisms as well as the clinical implications of medication-aggravated and medication-induced myasthenic syndromes.

Myasthenia gravis and scleroderma: Two cases and a review of the literature

Myasthenia gravis is uncommon in patients with scleroderma, and when diagnosed is usually associated with previous use of d-penicillamine. Clinically, both myasthenia and scleroderma may present with fatigue, weakness and bulbar symptoms, so one of diagnoses may be delayed. We report two new cases and review clinical features of 12 other reported cases of co-existing scleroderma and myasthenia gravis, unrelated to previous d-penicillamine therapy. Co-occurrence of myasthenia and scleroderma was reported almost exclusively (13/14) in women with a mean latency of 7.03 years. Most patients (10/11) had seropositive generalized myasthenia, and there were no cases with exclusively ocular symptoms. Three patients with pre-existing myasthenia were safely treated with d-penicillamine. Myasthenia and scleroderma occur in the context of an underlying autoimmune diathesis, but their co-occurrence could be underreported as the recognition of either disorder may be delayed by overlapping clinical symptoms. Our findings also suggest that d-penicillamine may be cautiously used in selected patients with pre-existing scleroderma and myasthenia, when potential benefits outweigh the risk of possible myasthenia exacerbation.

Juvenile rheumatoid arthritis: therapeutic perspectives

Juvenile rheumatoid arthritis (JRA) is the most common childhood chronic systemic autoimmune inflammatory disease. The therapeutic approach to JRA has, to date, been casual and based on extensions of clinical experiences gained in the management of adult rheumatoid arthritis (RA). The physiology of inflammation has been systemically studied and this has led to the identification of specific therapeutic targets and the development of novel approaches to the management of JRA. The classical treatments of the disease such as methotrexate, sodium aurothiomalate and sulfasalazine, are not always effective in controlling RA and JRA. This has necessitated the development of novel agents for treating RA, most of which are biological in nature and are targeted at specific sites of the inflammatory cascades. These biological therapeutic strategies in RA have proved successful and are being applied in the management of JRA. These developments have been facilitated by the advances in molecular biology which have heralded the advent of biodrugs (recombinant proteins) and gene therapy, in which specific genes can be introduced locally to enhance in vivo gene expression or suppress gene(s) of interest with a view to down-regulating inflammation. Some of these biodrugs, such as anti-tumor necrosis factor alpha (anti-TNFalpha), monoclonal antibodies (infliximab, adalimumab), TNF soluble receptor constructs (etanercept) and interleukin-1 receptor antagonist (IL-1Ra) have been tested and shown to be effective in RA. Etanercept has now been licensed for JRA. Clinical trials of infliximab in JRA are planned. Studies show that the clinical effects are transient, necessitating repeated treatments and the risk of vaccination effects. Anti-inflammatory cytokines such as IL-4, IL-10, transforming growth factor-beta and interferon-beta (IFN-beta) are undergoing clinical trials. Many of these agents have to be administered parenterally and production costs are very high; thus, there is a need, especially for pediatric use, to develop agents that can be taken orally. Long-term studies will be required to assess the tolerability and toxicity of these approaches in JRA, since cytokines and other mediators play important roles in host defenses, and the chronic inhibition, exogenous administration or constitutive over-expression of some cytokines/mediators may have undesirable effects.

Neuromuscular complications of connective tissue diseases

The connective tissue diseases, such as rheumatoid arthritis, Sjögren's syndrome, systemic lupus erythematosus, systemic sclerosis, and vasculitis, may cause various disorders of the peripheral nervous system. In this review, the clinical effects of the connective tissues diseases on nerve and muscle are examined with particular attention to mononeuritis multiplex, distal symmetric neuropathy, fulminant motor neuropathy, compression neuropathy, sensory neuronopathy, and trigeminal sensory neuropathy.

T cell responses to D-penicillamine in drug-induced myasthenia gravis: recognition of modified DR1:peptide complexes

The anti-rheumatoid drug D-penicillamine (D-pen) has a reactive sulfhydryl group capable of modifying self antigens, and can provoke typical autoantibody-mediated myasthenia gravis (MG), especially in DR1+ individuals. We have selected T cell clones from one such patient that were highly specific for D-pen but not its L-isomer or D-cysteine. Moreover, they were restricted to HLA-DR1, had a Th1 phenotype and used TCR V alpha4.1, V beta6.1. They responded well to blood mononuclear cells prepulsed with D-pen either in the absence of serum or after chloroquine treatment, but not to autologous D-pen-pulsed B cell lines. Thus, D-pen may directly couple to distinctive peptides resident in surface DR1 molecules on circulating macrophages or dendritic cells.

Lethargy in a patient with cirrhosis

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Myasthenia gravis and primary biliary cirrhosis. Common immunological features and rare coincidence

A 43-year-old woman with recently diagnosed primary biliary cirrhosis developed antibody-negative myasthenia gravis. She did not receive D-penicillamine therapy. Clinical and immunological features of this patient are discussed. In previous reports on an association between primary biliary cirrhosis and myasthenia D-penicillamine treatment was an obligate causal linkage between both disorders.

Ocular myasthenia: a protean disorder

Ocular myasthenia is a localized form of myasthenia clinically involving only the extraocular, levator palpebrae superioris, and/or orbicularis oculi muscles. Ocular manifestations can masquerade as a variety of ocular motility disorders, including cranial nerve and gaze palsies. A history of variable and fatiguable muscle weakness suggests this diagnosis, which may be confirmed by the edrophonium (Tensilon) test and acetylcholine receptor antibody titer. Anticholinesterases, corticosteroids and other immunosuppressive agents, and other therapeutic modalities, including thymectomy and plasmapheresis, are used in treatment. As the pathophysiology of myasthenia has been elucidated in recent years, newer treatment strategies have evolved, resulting in a much more favorable prognosis than several decades ago. This review provides historical background, pathophysiology, immuno-genetics, diagnostic testing, and treatment options for ocular myasthenia, as well as a discussion of drug-induced myasthenic syndromes.

Myasthenia gravis: an autoimmune response against the acetylcholine receptor

Myasthenia gravis (MG) is an organ-specific autoimmune disease caused by an antibody-mediated assault on the muscle nicotinic acetylcholine receptor (AChR) at the neuromuscular junction. Binding of antibodies to the AChR leads to loss of functional AChRs and impairs the neuromuscular signal transmission, resulting in muscular weakness. Although a great deal of information on the immunopathological mechanisms involved in AChR destruction exists due to well-characterized animal models, it is not known which etiological factors determine the susceptibility for the disease. This review gives an overview of the literature on the AChR, MG and experimental models for this autoimmune disease.

Iatrogenic inferior rectus palsy

We examined two patients who developed unilateral inferior rectus muscle palsy following inferior oblique myectomy. Surgical exploration showed a normal inferior rectus muscle and tendon in both patients. Surgical correction consisted of inferior rectus resection in one patient and inferior rectus resection combined with an ipsilateral superior rectus recession in the other. We propose inadvertent excision of the lateral portion of the inferior rectus muscle during inferior oblique myectomy as the probable mechanism of inferior rectus injury.

Clinical features, pathogenesis and management of drug-induced rhabdomyolysis

Striated musculature is considered unusually tolerant to all kinds of injuries, and rhabdomyolysis associated with drug overdose or chronic drug intake is a rare event. This may be because striated musculature, in contrast to other tissues such as liver and kidney, shows little affinity for most drugs. Several different types of drug-induced rhabdomyolysis may be distinguished, and the clinical features of the condition may vary widely, from moderate myalgia to involvement of groups of muscles to involvement of the total skeletal musculature. In clinically asymptomatic rhabdomyolysis, early diagnosis is only made if routine laboratory tests include determination of serum creatine kinase. Determination of myoglobin in serum and urine is more sensitive and allows earlier diagnosis of muscle necrosis. Myoglobinaemia may lead to toxin-induced tubular necrosis, and impairment of renal function or even acute renal failure. About 10% of all cases of acute renal failure are due to rhabdomyolysis. Fulminant rhabdomyolysis may be associated with excessive hyperkalaemia and hypocalcaemia which may induce further life-threatening complications. Therefore, early diagnosis of rhabdomyolysis is most important for prevention of its potentially life-threatening sequelae. Therapy of rhabdomyolysis consists of supportive and specific measures. Early diagnosis may help to prevent life-threatening sequelae like acute renal failure, electrolyte imbalance and shock. Withdrawal of the incriminated drug or detoxification in drug overdose should be followed by supportive measures including infusion therapy and correction of dehydration and electrolyte imbalances. Forced diuresis with sodium bicarbonate may protect the kidney function from acidosis and precipitation of myoglobin in tubules. Elimination of myoglobin from plasma may be enhanced by plasmapheresis. In patients with acute renal failure, haemodialysis is necessary. In malignant hyperthermia, immediate infusion of dantrolene sodium is required. This drug also seems to have a beneficial effect in neuroleptic malignant syndrome. The repair mechanisms of striated musculature function extremely well. The prognosis of muscular atrophy after the acute stage of rhabdomyolysis is excellent. The same is true for the prognosis of acute renal failure. However, the extent of complications or survival of the acute stage of rhabdomyolysis strongly depend on early diagnosis and start of adequate therapy.