Myasthenia Myasthenia gravisgravis

אפידמיולוגיהאפידמיולוגיה

prevalence - 20 per 100,000 prevalence - 20 per 100,000

population-between 53,000 and 60,000 population-between 53,000 and 60,000 cases /USAcases /USA

Pathophysiology of Myasthenia Pathophysiology of Myasthenia GravisGravis

Pathophysiology of Myasthenia Pathophysiology of Myasthenia GravisGravis

85% of patients with MG have detectable serum antibodies against AChRs20% to 40% of the remaining patients are positive for anti-MuSK antibodies about 10% of patients are double-seronegative MG anti-LRP4 autoantibodies exist in serum samples of patients with double-seronegative MG.

Autoantibodies in Myasthenia Gravis

Antigen MG ControlAnti-AChR Human 85-90%

TE671 80% 0

Anti-Musk 2-5% of all MG, >20% of AChR-SNMG

0

Anti-striated muscle

40% 4%

Anti-thyroid 44% 14%

Anti-nuclear 14-39% 4%

Anti-titin (MGT30) 85% (MG+thymoma) 0

Anti-ryanodine receptor

50% (MG+thymoma) 0

Evidence that MG is autoimmune Evidence that MG is autoimmune disease disease

MG Patients have increased incidence of other immune-MG Patients have increased incidence of other immune-mediated diseases, such as rheumatoid arthritismediated diseases, such as rheumatoid arthritis

A transitory neonatal form of the disease occurs in MG. A transitory neonatal form of the disease occurs in MG.

Immunosuppressive treatment, including plasma Immunosuppressive treatment, including plasma exchange, produces improvement in most patientsexchange, produces improvement in most patients

An animal model of MG can be produced by An animal model of MG can be produced by immunization with purified AChRimmunization with purified AChR

Antibodies against human AChR are found in the serum Antibodies against human AChR are found in the serum of most patientsof most patients

Evidence that MG is autoimmune Evidence that MG is autoimmune disease disease

Myasthenic serum or IgG produces abnormal Myasthenic serum or IgG produces abnormal neuromuscular transmission when injected into animalsneuromuscular transmission when injected into animals

IgG and complement components are attached to the IgG and complement components are attached to the postsynaptic endplate membrane in myasthenicpostsynaptic endplate membrane in myasthenic

Antibody-Mediated Mechanisms

Accelerated degradation of AChRsComplement-Mediated AChR-lossBlockade of AChRs

Possible Origin of Autoimmunity in MG

Cross reacting epitopeIdiotypic dysregulationAbnormal antigenDrug related antigenHelper T-cell defectRegulatory T-cell defect

AChR Seronegative Myasthenia Gravis

10-15% of MG patientsClinical presentation similar to seropositive generalized MGThymus 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 Seronegative MGAChR antibodies Yes No

Improvement after plasma exchange

Yes Yes

Defect transferable to mice by Ig

Yes Yes

Transfer features

NMT defect Yes YesAChR reduction Yes No

Antibody attached to AChR Yes No

Immunization against antigen(s)

Produces disease Not yet clear

AChR-positive MG (85-90%)

AChR-negative MG:– MuSK positive (around 20-40%)– MuSK negative (double negative)

Clinical PresentationClinical Presentation

Ptosis or diplopia was the initial symptom Ptosis or diplopia was the initial symptom in two thirds in two thirds Almost all have both within 2 years of Almost all have both within 2 years of disease onsetdisease onsetDifficulty chewing, swallowing, or talking is Difficulty chewing, swallowing, or talking is the initial symptom in one sixth of patients the initial symptom in one sixth of patients and limb weakness in one tenth. and limb weakness in one tenth. Weakness typically fluctuates during Weakness typically fluctuates during the day . the day .

Clinical Presentation:Clinical Presentation:

Disease course Disease course

MG is variable but usually progressive MG is variable but usually progressive Restricted to the ocular muscles in 10%-40% of Restricted to the ocular muscles in 10%-40% of patients patients Maximum weakness occurs during the first year Maximum weakness occurs during the first year in two thirds of patients. in two thirds of patients. Before corticosteroids were usedBefore corticosteroids were used for for treatment, approximately one third of patients treatment, approximately one third of patients had spontaneous improvement, one third had had spontaneous improvement, one third had progressive disease, and one third died of the progressive disease, and one third died of the disease. disease.

Factors that worsen myasthenic Factors that worsen myasthenic symptomssymptoms

Emotional upset,Emotional upset,

Systemic illness (especially viral Systemic illness (especially viral respiratory infections).respiratory infections).

Hypothyroidism / hyperthyroidism.Hypothyroidism / hyperthyroidism.

Pregnancy, the menstrual cycle,Pregnancy, the menstrual cycle,

Drugs affecting neuromuscular Drugs affecting neuromuscular transmission transmission

Fever. Fever.

Physical FindingsPhysical Findings Ocular MusclesOcular Muscles -Asymmetrical weakness -Asymmetrical weakness of several muscles in both eyes is typical. of several muscles in both eyes is typical.

Ptosis is usually asymmetrical and varies Ptosis is usually asymmetrical and varies during sustained activity during sustained activity

OropharyngealOropharyngeal MusclesMuscles changes in the changes in the voice, difficulty chewing and swallowing voice, difficulty chewing and swallowing

Limb MusclesLimb Muscles Neck flexors are usually Neck flexors are usually weaker than neck extensors, deltoids, weaker than neck extensors, deltoids, triceps, and wrist/fingers extensors are triceps, and wrist/fingers extensors are often weaker than other muscles. often weaker than other muscles.

OCCULAR SYMPTOMESOCCULAR SYMPTOMESWeakness usually involves one or more ocular muscles Weakness usually involves one or more ocular muscles without overt pupillary abnormalitywithout overt pupillary abnormalityWeakness is typically variable, fluctuating, and fatigableWeakness is typically variable, fluctuating, and fatigableAfter down gaze, upgaze produces lid overshoot ("lid After down gaze, upgaze produces lid overshoot ("lid twitch").twitch").Pseudo-internuclear ophthalmoplegia-limited adduction Pseudo-internuclear ophthalmoplegia-limited adduction is present, with nystagmoid jerks in abducting eye.is present, with nystagmoid jerks in abducting eye. In asymmetrical ptosis, covering the eye with the ptotic In asymmetrical ptosis, covering the eye with the ptotic lid may relieve contraction of the opposite frontalis.lid may relieve contraction of the opposite frontalis.Passively lifting a ptotic lid may cause the opposite lid to Passively lifting a ptotic lid may cause the opposite lid to fall.fall.Cold applied to the eye may improve lid ptosis.Cold applied to the eye may improve lid ptosis.

קקליניקהקקליניקהחולשת שרירים •

מתקדמת: העפעפיים

והעיניים, פנים, דיבור, בליעה, צוואר, גפיים,

נשימה

• myasthenic crisis

תימומה •

Clinical association of MuSK abs

Distinct populationAge at onset around third decadeMore women than menMore bulbar patientsResponse to plasma exchangeIncidence 20-40% of AChR negative MG(Possible additional plasma factor involved ?)

The Thymus in Myasthenia The Thymus in Myasthenia GravisGravis

Breakdown in immune tolerance toward self-Breakdown in immune tolerance toward self-antigens in the thymus. antigens in the thymus. 10% of patients with MG have a thymic tumor 10% of patients with MG have a thymic tumor most are benign.most are benign.70% have hyperplastic changes (germinal 70% have hyperplastic changes (germinal centers) that indicate an active immune responsecenters) that indicate an active immune responseVirtually all patients with MG and thymoma have Virtually all patients with MG and thymoma have elevated concentrations of AChR-binding elevated concentrations of AChR-binding antibodies antibodies

Diagnostic Procedures-1Diagnostic Procedures-1

Edrophonium Chloride (Tensilon) TestEdrophonium Chloride (Tensilon) Test

positive in more than 90% of patients with positive in more than 90% of patients with MG MG

Tensilon TestTensilon Test is not unique to MG is not unique to MG

A dose of 2 mg is injected intravenously, A dose of 2 mg is injected intravenously, and the response is monitored for 60 and the response is monitored for 60 seconds. Then 3 and 5 mg.seconds. Then 3 and 5 mg.

ElectromyographyElectromyography

10% decrement in amplitude when the first 10% decrement in amplitude when the first stimulus is compared to the fourth or fifthstimulus is compared to the fourth or fifth

SFEMG is the most sensitive clinical test SFEMG is the most sensitive clinical test of neuromuscular transmission and shows of neuromuscular transmission and shows increased jitter . increased jitter .

Diagnostic Procedures-2Diagnostic Procedures-2

Diagnostic Procedures-2Diagnostic Procedures-2

TreatmentTreatment

Cholinesterase Inhibitors- Mestinon 30-Cholinesterase Inhibitors- Mestinon 30-60 mg/4-8/day60 mg/4-8/day

CorticosteroidsCorticosteroids 75% of patients markdly 75% of patients markdly improved ! improved ! Prednisone 1.5-2.0 mg/kg per day Prednisone 1.5-2.0 mg/kg per day

Immunosuppressant Immunosuppressant Drugs-Drugs-

Plasma ExchangePlasma Exchange ,IVIG,IVIG

ThymectomyThymectomy

Treatment-2Treatment-2

AzathioprineAzathioprine

Onset action: 4-8  Onset action: 4-8  

side effects: allergic reaction,hepatic toxicity, side effects: allergic reaction,hepatic toxicity, leukopenialeukopenia

CyclosporinCyclosporin  Onset action: 2-3 renal toxicity,   Onset action: 2-3 renal toxicity, hypertension, multiple potential drug interactionshypertension, multiple potential drug interactions

CyclophosphamideCyclophosphamide  Onset action: variabl     Onset action: variabl  

side effects: leukopenia, hair loss, cystitisside effects: leukopenia, hair loss, cystitis

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 yearsDuring this period the efficacy of PE was evaluated: the response rate was over 85 % of patients (improved).

Efficacy of PE in myasthenia gravis: Hadassah experience

Myasthenia gravis:Myasthenic crisis

After Plasmapheresis

Before Plasmapheresis

What do we treat patients with MG when the conventional therapy fails?

Current therapy of myasthenia gravis

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 membraneNeutralizing soluble serum factors

mAb therapy for neuro-inflammatory diseases

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

Monoclonal Abs directed at specific immunologic aspects of MG.

36

Examples of Therapeutic Monoclonal Antibodies

Name Antigenic target Clinical use

Muromomab CD3 Transplant rejection

Daclizumab CD25 Transplant rejection,adult T-cell leukemia

Rituximab CD20 B-cell lymphoma, AUTOIMMUNITY

Infliximab TNF Crohn’s disease, RA

Alemtuzumab CD52 CLL,MS

Adalimumab TNF RA

Efalizumab CD11a Psoriasis

NatalizumabABT-874

α-4 integrinAnti IL-12

MS, Crohn’s diseaseNot yet identified

Toralizuma CD40L, CD154 ineffective in SLENo candidate Non Fc-binding Not yet identified

Eculizumab Anti-C5 paroxysmal nocturnal hemoglobinuria and atypical hemolytic-uremic

syndrome

Abatacept Anti-CTLA4 ineffective in SLE

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

Targeting B-cells

39

Rituximab: Anti-CD20Target 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 CD20-expressing 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-dependent cytotoxicity or to generation of human antichimeric antibodies (HACA).

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.

The role of B-cell activating factor (BAFF) in myasthenia gravis

41

Belimumab : Anti-BAFFTarget 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 erythematosisA phase II trial in rheumatoid arthritis was encouraging but no phase III trial is underway. A phase II trial in MG has been announced

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.

Therapy that targets complement

43

Eculizumab : Anti-C5Target 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

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

Agents targeting T cell intracellular signaling pathways, and costimulation

45

Daclizumab: Anti-CD25Target IL-2 receptor α 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

Association of Myasthenia Association of Myasthenia Gravis with Other DiseasesGravis with Other Diseases

Hyperthyroidism Hyperthyroidism

Rheumatoid arthritis. Rheumatoid arthritis. ~2% ~2%

Seizures Seizures

diabetes mellitus 7%diabetes mellitus 7%

thyroid disease 6%thyroid disease 6%

nonthymus neoplasm 3%, nonthymus neoplasm 3%,

Transitory Neonatal Transitory Neonatal Myasthenia.Myasthenia.

10-20% of newborns of MG mothers10-20% of newborns of MG mothers

frequency and severity correlate with frequency and severity correlate with antibody levelantibody level

Hypotonia and poorly fed during the first 3 Hypotonia and poorly fed during the first 3 days. symptoms may be delayed for 1-2 days. symptoms may be delayed for 1-2 days. Usually last less than 2 weeks but days. Usually last less than 2 weeks but may continue for as long as 12 weeks. may continue for as long as 12 weeks.

Genetic Myasthenic SyndromesGenetic Myasthenic Syndromes

not immune mediated not immune mediated 2:1 male predominance. 2:1 male predominance. ophthalmoparesis and ptosis during ophthalmoparesis and ptosis during infancy. Limb weakness is usually mild infancy. Limb weakness is usually mild compared with ophthalmoplegia.compared with ophthalmoplegia.Respiratory distress is unusual. Respiratory distress is unusual. ChE inhibitors improve limb muscle ChE inhibitors improve limb muscle weakness in many forms of congenital weakness in many forms of congenital genetic myasthenia genetic myasthenia

Lambert-Eaton Myasthenic Lambert-Eaton Myasthenic SyndromeSyndrome

A pre-synaptic abnormality of ACh release A pre-synaptic abnormality of ACh release In association with malignancy, usually small cell lung In association with malignancy, usually small cell lung cancer (SCLC). cancer (SCLC). Abs against the voltage-gated calcium channels Abs against the voltage-gated calcium channels (VGCCs) on nerve terminals(VGCCs) on nerve terminalsreduced tendon reflexes and enhanced by repeated reduced tendon reflexes and enhanced by repeated muscle contraction or repeated tapping of the tendon. muscle contraction or repeated tapping of the tendon. autonomic dysfunction :dry mouth, impotence and autonomic dysfunction :dry mouth, impotence and postural hypotension. postural hypotension. Treatment with Guanidine hydrochloride increases the Treatment with Guanidine hydrochloride increases the release of ACh release of ACh

Drug alert for patients with Drug alert for patients with myasthenia gravismyasthenia gravis

Interferon-α, Interferon-α, botulinum toxinbotulinum toxin, and d-penicillamine should never be , and d-penicillamine should never be used in myasthenic patients. used in myasthenic patients. The following drugs produce worsening of myasthenic weakness The following drugs produce worsening of myasthenic weakness in most patients who receive them. Use with caution and monitor in most patients who receive them. Use with caution and monitor patient for exacerbation of myasthenic symptoms. patient for exacerbation of myasthenic symptoms.

– Succinylcholine, Succinylcholine, dd-tubocurarine, or other neuromuscular--tubocurarine, or other neuromuscular-blocking agents blocking agents

– Quinine, quinidine, and procainamide Quinine, quinidine, and procainamide – Aminoglycoside antibiotics, particularly gentamicin, Aminoglycoside antibiotics, particularly gentamicin,

kanamycin, neomycin, and streptomycin kanamycin, neomycin, and streptomycin – Beta blockers (systemic and ocular preparations): propranolol, Beta blockers (systemic and ocular preparations): propranolol,

timololtimolol maleate eyedrops maleate eyedrops – Calcium-channel blockers Calcium-channel blockers – Magnesium salts (including laxatives and antacids with high Magnesium salts (including laxatives and antacids with high

Mg2+ concentrations) Mg2+ concentrations) – Iodinated contrast agents Iodinated contrast agents

Many other drugs are reported to exacerbate the weakness in Many other drugs are reported to exacerbate the weakness in some patients with MG. All patients with MG should be observed some patients with MG. All patients with MG should be observed for increased weakness whenever a new medication is started. for increased weakness whenever a new medication is started.

BOTULISMBOTULISM

A toxin produced by the anaerobic bacterium, A toxin produced by the anaerobic bacterium, Clostridium botulinumClostridium botulinum, , Blocks the release of ACh from the motor nerve terminal Blocks the release of ACh from the motor nerve terminal Intoxication usually follows ingestion of contaminated Intoxication usually follows ingestion of contaminated foods that were inadequately sterilized foods that were inadequately sterilized First Nausea and vomiting and then neuromuscular First Nausea and vomiting and then neuromuscular symptoms 12-36 hours after ingestion symptoms 12-36 hours after ingestion

Clinical symptoms:Clinical symptoms: blurred vision, dysphagia, and dysarthria. blurred vision, dysphagia, and dysarthria. Pupillary responses to light are impaired.Pupillary responses to light are impaired.tendon reflexes are variably reduced. tendon reflexes are variably reduced. Fatal respiratory paralysis may occur rapidly. Fatal respiratory paralysis may occur rapidly. Autonomic dysfunction, such as dry mouth, constipation, Autonomic dysfunction, such as dry mouth, constipation, or urinary retention in most. or urinary retention in most.