Myasthenia gravis אפידמיולוגיה prevalence - 20 per 100,000 population-between 53,000 and 60,000 cases /USA Pathophysiology of Myasthenia Gravis Pathophysiology of Myasthenia Gravis 85% of patients with MG have detectable serum antibodies against AChRs 20% to 40% of the remaining patients are positive for anti-MuSK antibodies about 10% of patients are doubleseronegative MG anti-LRP4 autoantibodies exist in serum samples of patients with doubleseronegative MG. Autoantibodies in Myasthenia Gravis Antigen Anti-AChR MG Control Human 85-90% 0 TE671 80% Anti-Musk 2-5% of all MG, >20% of AChR-SNMG 0 Anti-striated muscle Anti-thyroid 40% 4% 44% 14% Anti-nuclear 14-39% 4% Anti-titin (MGT30) 85% (MG+thymoma) 0 50% (MG+thymoma) 0 Anti-ryanodine receptor Evidence that MG is autoimmune disease MG Patients have increased incidence of other immunemediated diseases, such as rheumatoid arthritis A transitory neonatal form of the disease occurs in MG. Immunosuppressive treatment, including plasma exchange, produces improvement in most patients An animal model of MG can be produced by immunization with purified AChR Antibodies against human AChR are found in the serum of most patients Evidence that MG is autoimmune disease Myasthenic serum or IgG produces abnormal neuromuscular transmission when injected into animals IgG and complement components are attached to the postsynaptic endplate membrane in myasthenic Antibody-Mediated Mechanisms Accelerated degradation of AChRs Complement-Mediated AChR-loss Blockade of AChRs Possible Origin of Autoimmunity in MG Cross reacting epitope Idiotypic dysregulation Abnormal antigen Drug related antigen Helper T-cell defect Regulatory T-cell defect AChR Seronegative Myasthenia Gravis 10-15% of MG patients Clinical presentation similar to seropositive generalized MG Thymus usually “normal” Reduced-AChRs probably due to antibodies, to another NMJ antigen, or signal transduction effect on AChR function Autoimmune disorders applied to seropositive and seronegative MG Seropositive MG Yes Seronegative MG No Improvement after plasma exchange Yes Yes Defect transferable to mice by Ig Yes Yes NMT defect Yes Yes AChR reduction Yes No Antibody attached to AChR Yes No Immunization against antigen(s) Produces disease Not yet clear AChR antibodies Transfer features AChR-positive MG (85-90%) AChR-negative MG: – MuSK positive (around 20-40%) – MuSK negative (double negative) Clinical Presentation Ptosis or diplopia was the initial symptom in two thirds Almost all have both within 2 years of disease onset Difficulty chewing, swallowing, or talking is the initial symptom in one sixth of patients and limb weakness in one tenth. Weakness typically fluctuates during the day . Clinical Presentation: Disease course MG is variable but usually progressive Restricted to the ocular muscles in 10%-40% of patients Maximum weakness occurs during the first year in two thirds of patients. Before corticosteroids were used for treatment, approximately one third of patients had spontaneous improvement, one third had progressive disease, and one third died of the disease. Factors that worsen myasthenic symptoms Emotional upset, Systemic illness (especially viral respiratory infections). Hypothyroidism / hyperthyroidism. Pregnancy, the menstrual cycle, Drugs affecting neuromuscular transmission Fever. Physical Findings Ocular Muscles -Asymmetrical weakness of several muscles in both eyes is typical. Ptosis is usually asymmetrical and varies during sustained activity Oropharyngeal Muscles changes in the voice, difficulty chewing and swallowing Limb Muscles Neck flexors are usually weaker than neck extensors, deltoids, triceps, and wrist/fingers extensors are often weaker than other muscles. OCCULAR SYMPTOMES Weakness usually involves one or more ocular muscles without overt pupillary abnormality Weakness is typically variable, fluctuating, and fatigable After down gaze, upgaze produces lid overshoot ("lid twitch"). Pseudo-internuclear ophthalmoplegia-limited adduction is present, with nystagmoid jerks in abducting eye. In asymmetrical ptosis, covering the eye with the ptotic lid may relieve contraction of the opposite frontalis. Passively lifting a ptotic lid may cause the opposite lid to fall. Cold applied to the eye may improve lid ptosis. קקליניקה • חולשת שרירים מתקדמת: העפעפיים והעיניים ,פנים, דיבור ,בליעה, צוואר ,גפיים, נשימה • myasthenic crisis • תימומה Clinical association of MuSK abs Distinct population Age at onset around third decade More women than men More bulbar patients Response to plasma exchange Incidence 20-40% of AChR negative MG (Possible additional plasma factor involved ?) The Thymus in Myasthenia Gravis Breakdown in immune tolerance toward selfantigens in the thymus. 10% of patients with MG have a thymic tumor most are benign. 70% have hyperplastic changes (germinal centers) that indicate an active immune response Virtually all patients with MG and thymoma have elevated concentrations of AChR-binding antibodies Diagnostic Procedures-1 Edrophonium Chloride (Tensilon) Test positive in more than 90% of patients with MG Tensilon Test is not unique to MG A dose of 2 mg is injected intravenously, and the response is monitored for 60 seconds. Then 3 and 5 mg. Diagnostic Procedures-2 Electromyography 10% decrement in amplitude when the first stimulus is compared to the fourth or fifth SFEMG is the most sensitive clinical test of neuromuscular transmission and shows increased jitter . Diagnostic Procedures-2 Treatment Cholinesterase Inhibitors- Mestinon 3060 mg/4-8/day Corticosteroids 75% of patients markdly improved ! Prednisone 1.5-2.0 mg/kg per day Immunosuppressant DrugsPlasma Exchange ,IVIG Thymectomy Treatment-2 Azathioprine Onset action: 4-8 side effects: allergic reaction,hepatic toxicity, leukopenia Cyclosporin Onset action: 2-3 renal toxicity, hypertension, multiple potential drug interactions Cyclophosphamide Onset action: variabl side effects: leukopenia, hair loss, cystitis Efficacy of PE in myasthenia gravis: Hadassah experience 86 myasthenic patients were treated with repeated courses of PE (ranging from 6-126 exchanges during a period of 3 years) The follow up period was 3 years During this period the efficacy of PE was evaluated: the response rate was over 85 % of patients (improved). Myasthenia gravis: Myasthenic crisis Before Plasmapheresis After Plasmapheresis Current therapy of myasthenia gravis What do we treat patients with MG when the conventional therapy fails? mAb therapy for neuro-inflammatory diseases Monoclonal antibodies (mAbs) represent an emerging and rapidly growing field of therapy in neuro-inflammatory diseases . Most of them have been developed in systemic autoimmune diseases and Oncology. There are currently more the 240 mAbs in clinical development mAb therapy for neuro-inflammatory diseases Monoclonal antibodies mode of action: Depletion of specific cells Blocking specific molecules expressed on the cell membrane Neutralizing soluble serum factors Monoclonal Abs directed at specific immunologic aspects of MG Abnormal B cells activation Complement activation BAFF disregulation Helper and Regulatory T-cell defect Monoclonal Abs directed at specific immunologic aspects of MG. Dalakas , Ann N Y Acad Sci, 2012 Examples of Therapeutic Monoclonal Antibodies Name Antigenic target Clinical use Muromomab CD3 Transplant rejection Daclizumab CD25 Transplant rejection,adult T- cell leukemia Rituximab CD20 Infliximab TNF Crohn’s disease, RA CD52 CLL,MS TNF RA CD11a Psoriasis Natalizumab ABT-874 -4 integrin Anti IL-12 MS, Crohn’s disease Not yet identified Toralizuma CD40L, CD154 ineffective in SLE No candidate Non Fc-binding Not yet identified Eculizumab Anti-C5 paroxysmal nocturnal hemoglobinuria and atypical hemolytic-uremic syndrome Abatacept 36 Anti-CTLA4 ineffective in SLE Alemtuzumab Adalimumab Efalizumab B-cell lymphoma, AUTOIMMUNITY Targeting B-cells AChR + MG is the prototypic antibody mediated disease with clear evidence that AChR antibodies induce the disease in animal models and in humans. Both AChR and MuSK antibody positive patients respond to plasma exchange. Anti-MuSK patients do not appear to respond to IVIg. Anti-MuSK antibodies are IgG4 which do not activate complement. Anti-AChR are IgG1 and IgG3 that activate complement. Targeting B-cells B-cell targeting therapies: Rituximab Ocrelizumab Ofatumumab Rituximab: Anti-CD20 Target CD-20 receptor Other names Mabthera Rituxan, and Zytux Rationale B cells involvement in autoimmune diseases – antibody mediated , B cells role as APCs and cytokines production Mode of action The antibody binds to CD20 expressed on B cells, from early pre-B cells to later in differentiation, but absent on terminally differentiated plasma cells. eliminates nearly all CD20expressing B cells by CDC and ADCC as well as induction of apoptosis Safety and tolerability Severe infusion reaction, cardiac arrest, Infections – PML. Resistance development, most likely due to less efficient antibody- 39 dependent cytotoxicity or to generation of human antichimeric antibodies (HACA). The role of B-cell activating factor (BAFF) in myasthenia gravis B-cell activating factor (BAFF) is important in the differentiation and maturation of B cells and plasma cells. Although the mechanism(s) by which BAFF and its receptors help regulate B-cell function and tolerance is not known, it may play a significant role in the immune process involved in myasthenia gravis. Serum BAFF levels were found to be significantly higher in MG patients compared to controls including those with MS There was no correlation to disease severity but a trend for levels to be higher in AChR + patients. There is also evidence that BAFF is upregulated in germinal follicle like structures in myasthenic thymuses. Belimumab : Anti-BAFF Target BAFF Other names Anti-BAFF Rationale BAFF- is important in the differentiation and maturation of B cells and plasma cells Mode of action inhibits BAFF action via binding circulating BAFF and reducing the number of circulating B-cells but not to the extent as rituximab Safety and tolerability approved in the US, Canada and Europe for the treatment of systemic lupus erythematosis 41 A phase II trial in rheumatoid arthritis was encouraging but no phase III trial is underway. A phase II trial in MG has been announced Therapy that targets complement Complement mediated damage to the postsynaptic junction has been demonstrated to bind to the AChR-antibody complex inducing membrane-attack-complex damage to the membrane reducing post-synaptic folds, widening the synaptic cleft and reducing the numbers of receptors. Eculizumab : Anti-C5 Target complement protein C5 Other names Soliris Rationale Complement mediated damage to the post-synaptic junction has been demonstrated to bind to the AChR-antibody complex inducing membrane-attack-complex damage to the membrane reducing post-synaptic folds, widening the synaptic cleft and reducing the numbers of receptors. Mode of action a recombinant humanized monoclonal IgG 2/4 antibody that binds to complement protein C5 which prevents the generation of the terminal complement C5b-9 complex Safety and tolerability nausea, back pain, nasopharyngitis, and headache vulnerable to infection with encapsulated organisms. meningococcal vaccination is recommended at least 2 weeks prior to receiving eculizumab 43 Agents targeting T cell intracellular signaling pathways, and costimulation IL-2 mediate cell proliferation and differentiation. Daclizumab binds to CD25 (IL-2 receptor antagonist) and inhibits T cell proliferation. Daclizumab is very well tolerated, has been approved for one form of leukemia, and has been very promising in patients with multiple sclerosis in at least two clinical trials. Daclizumab An excellent agent to consider for MG Daclizumab: Anti-CD25 Target IL-2 receptor chain (CD25) Other names Anti-CD25, Zenapax® Rationale IL-2 mediate cell proliferation and differentiation. Mode of action Prevents IL-2 binding without triggering of complement- or cell-mediated cell depletion, modulation of the IL-2 receptor complex or induction of intracellular signaling events a marked expansion of regulatory CD56bright NK cells Safety and tolerability Gastrointestinal (e.g. nausea, diarrhoea), metabolic and nutritional disorders 45 Association of Myasthenia Gravis with Other Diseases Hyperthyroidism Rheumatoid arthritis. ~2% Seizures diabetes mellitus 7% thyroid disease 6% nonthymus neoplasm 3%, Transitory Neonatal Myasthenia. 10-20% of newborns of MG mothers frequency and severity correlate with antibody level Hypotonia and poorly fed during the first 3 days. symptoms may be delayed for 1-2 days. Usually last less than 2 weeks but may continue for as long as 12 weeks. Genetic Myasthenic Syndromes not immune mediated 2:1 male predominance. ophthalmoparesis and ptosis during infancy. Limb weakness is usually mild compared with ophthalmoplegia. Respiratory distress is unusual. ChE inhibitors improve limb muscle weakness in many forms of congenital genetic myasthenia Lambert-Eaton Myasthenic Syndrome A pre-synaptic abnormality of ACh release In association with malignancy, usually small cell lung cancer (SCLC). Abs against the voltage-gated calcium channels (VGCCs) on nerve terminals reduced tendon reflexes and enhanced by repeated muscle contraction or repeated tapping of the tendon. autonomic dysfunction :dry mouth, impotence and postural hypotension. Treatment with Guanidine hydrochloride increases the release of ACh Drug alert for patients with myasthenia gravis Interferon-α, botulinum toxin, and d-penicillamine should never be used in myasthenic patients. The following drugs produce worsening of myasthenic weakness in most patients who receive them. Use with caution and monitor patient for exacerbation of myasthenic symptoms. – Succinylcholine, d-tubocurarine, or other neuromuscularblocking agents – Quinine, quinidine, and procainamide – Aminoglycoside antibiotics, particularly gentamicin, kanamycin, neomycin, and streptomycin – Beta blockers (systemic and ocular preparations): propranolol, timolol maleate eyedrops – Calcium-channel blockers – Magnesium salts (including laxatives and antacids with high Mg2+ concentrations) – Iodinated contrast agents Many other drugs are reported to exacerbate the weakness in some patients with MG. All patients with MG should be observed for increased weakness whenever a new medication is started. BOTULISM A toxin produced by the anaerobic bacterium, Clostridium botulinum, Blocks the release of ACh from the motor nerve terminal Intoxication usually follows ingestion of contaminated foods that were inadequately sterilized First Nausea and vomiting and then neuromuscular symptoms 12-36 hours after ingestion Clinical symptoms: blurred vision, dysphagia, and dysarthria. Pupillary responses to light are impaired. tendon reflexes are variably reduced. Fatal respiratory paralysis may occur rapidly. Autonomic dysfunction, such as dry mouth, constipation, or urinary retention in most.