Myasthenia Gravis.mansfans.com

Myasthenia gravis BY

Prof.Dr/ Ahmed Gamal AZab

Definition A

chronic disease with tendency to remit and to relapse , characterized by abnormal muscular fatigability .

Pathogenesis  It

is due to an autoimmune process in which antibodies against acetylcholine receptors cause a disordered conduction in myoneural junction.

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Pathology  Characteristic

clusters of lymphocytes ( lymphorrhages) in between the muscle fibres.  Thymus gland : may show hyperplasia or a thymic tumor (thymoma) .

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Incidence  Female

: male = 2 : 1  Mean age of onset : 26y in F, 30y in M.  Close relationship w/thyrotoxicosis, SLE, rheumatoid arthritis, biliary cirrhosis, M.S, and cancer.

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Clinical picture  Gradual

onset , progressive course w/remissions.  It has a characteristic descending march course ,affecting occular muscles followed by facial, bulbar then skeletal muscles { upper before lower limb, proximal > distal }.  No muscle wasting, smooth muscles are not involved. www.MansFans.com

Fluctuations in myasthenia 1- On action : eating, talking, walking. 2- Diurnal variation. 3- Spontaneous remission & relapse.

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Diagnosis 1- Clinical fatigue tests : inducing fatigue by asking the patient to count to 100 { > dysarthria } or maintain looking up { > ptosis } . 2- Prostigmine test { 1.5mg prostigmine + 0.5mg atropine IM }. 3- Tensilon test { edrophonium HCL} : 2mg iv followed,if no idiosyncrasy ,by 8mg > improve myasthenia after a minute. 4- EMG : repititive stimulation test >diminished amplitude after repeated stimulation . www.MansFans.com

Diagnosis { cont..} 5- Detection of anti Ach R antibodies : the most sensitive test. 6- Chest tomogram : to detect thymoma or thymic hyperplasia . 7- Thyroid function test. 8- Tests for collagen disorders,R/O malignancy

Treatment 1- Anticholine esterases : mestinon , prostigmine : titrate until adequate response. 2- Prednisolone : Initially 50 mg daily,tapered gradually to a maintenance of 5 mg/day. 3- Imuran { azathioprine } : 2mg/Kg/day. 4- Plasmapheresis : to get rid of harmful antibodies. 5- Thymectomy : obligatory for thymoma or thymic hyperplasia. 6- IVIG : 0.4 gm/Kg/day for 5 succesive days. www.MansFans.com

Crisis in Myasthenia It is a severe deterioration in a myasthenic patient . Types: 1- Myasthenic crisis : exacerbated disease process. C/P :pupillary dilatation, flushed face, dry mouth, dry skin,constipation and tachycardia. 2- cholinergic crisis (drug overdosage ) : pupillary constriction, pallor, excessive salivation, sweating, diarrhea and bradycardia .

Management of Crisis - ICU admission . - Mechanical ventillation. - Stop all medications. - Tensilon test for differentiation. - Plasmapheresis or IVIG for myasthenic crisis. - Antibiotics, naso-gastric tube feeding. - Avoid : phenytoins, aminoglycosides, ampicillin, propranolol, morphia, barbiturates { has a neuromuscular blocking effect } . - Later on : re-introduce drugs in a proper dosage.

Neonatal myasthenia  Seen

in infants from a myasthenic mother , recovers spontaneously between 1week – 3 months after delivery.  It is due to antibodies from the mother serum.

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Lambert-Eaton(myasthenic-myopathic) syndrome  Often

associated w/ bronchogenic carcinoma or other malignancies.  Proximal weakness, wasting with myasthenic fatigability.  No Ach R antibodies.  No significant response to prostigmine , but respond to guanidine HCL 20mg/Kg/day or prednisolone + imuran. www.MansFans.com