Myasthenia

1- Introduction / clinic:

– Immunological diseases related receptor blockade by the endplate acetylcholine receptors anti-Ac, resulted in excessive fatig reliability of striated muscles, improved by rest.

– Myasthenic phenomenon is a deficit in muscle strength whose essential character is to increase the opportunity of an effort. The fatigue increases during the day. This fatigue is corrected at rest.

Myasthenia– An essential feature of this is its correction under the effect of anti-cholinesterase drugs. The cold improves.

– Involvement of the eye-lid musculature is evocative. Ptosis (+ or diplopia) is one-sided to the top and can bilateralize thereafter remaining asymmetric habi-rently. It tends to increase later in the day.

– Achieving the bulbar muscle innervation sounds on phonation, mastication (with food) and swallowing (liquid discharge through the nose). The voice becomes intelligible nasonnée then.

– Achievement of limb muscles predominates on the proximal muscles (shoulder girdle). Myalgias are misleading.

– Involvement of respiratory muscles can lead to a rapid ventilatory decompensation sometimes inaugural.

– Negative signs: normal ROT; no sensory disorders; lack of muscle atrophy; lack of sphincter disorders.

– Signs of overdose in cholinesterase drugs (cholinergic crisis): abundant fasciculations, increased muscle weakness, nausea, vomiting, diarrhea, colic, tearing sweating, paleness, miosis, bradycardia.

– Transient neonatal myasthenia occurs in 10 to 25% of myasthenic mother of children. Early events for 2 to 3 weeks and then spontaneously regress. Hypotonia associated with the suction disorders, swallowing and breathing.

2- Associations:

– Thymus and gravis: thymic hyperplasia exists in 65% of cases and thymoma in 15% of cases. The thymectomies have a beneficial effect especially in cases of mere hyperplasia. Thymoma can be benign or malignant.

– Myasthenia and autoimmune diseases: associations are common. thyroid disease is found in 13% of cases.

An association with cancer is not exceptional.

3- Additional tests:

– EMG: presence of neuromuscular blockade after a repetitive low frequency stimulation (3Hz) with decrease in the amplitude of the muscular response (reduction potential of more than 10%).

NB: The most sensitive test is the single fiber EMG.

– Pharmacological test: test edrophonium (Tensilon) and prostigmine (cholinesterase inhibitors). This test temporarily regress symptoms. If it is negative does not exclude the diagnosis.

– Anti-receptor Ac acetylcholine: positive in more than 85% in case of generalized MG. Positive in 50% of ocular myasthenia. Free rate correlated with the clinical severity.

– Chest Scanner: search for thymoma or thymic hyperplasia.

Testing the ice (less reliable) is transiently disappear ptosis

4- Classification:

– Group I: isolated eye shape

– Group II: little intense generalized form without respiratory muscle

– IIA: without reaching pharyngeal

– IIB: with involvement pharyngeal

– Group III: acute myasthenia gravis, severe, generalized with respiratory illness

– Group IV: myasthenia gravis, late

5- Respiratory Impairment two mechanisms:

– Acute myasthenic crisis: with acute motor deficit requiring emergency resuscitation. 4 signs: dyspnea, false-roads, ineffective cough, bronchial congestion.

– Cholinergic crisis: due to overload of cholinesterase inhibitors with respiratory paralysis and cholinergic signs of overdose include nausea, sweating, hy-persalivation, abdominal pain, diarrhea, miosis, bradycardia.

– The factors triggering acute myasthenic crisis: infections, stress, pregnancy, postpartum anesthesia.

6- Treatment:

A- Anticholinesterases:

prostigmine; Tensilon. Side effects are nicotinic (cramps, twitching); muscarinic (sweat, saliva and bronchial hypersecretion, abdominal pain and diarrhea, miosis, bradycardia). If overdose risk cholinergic respiratory crisis.

B- Etiological treatment:

– Thymectomy: risk of postoperative myasthenic thrust. Offered in the young and in generalized myasthenia.

– Corticosteroids: May initial transient worsening

– Immunosuppressive: offered in case of failure of thymectomy and corticosteroid therapy (azathioprine)

– Plasmapheresis: in acute forms (myasthenic crisis) before thymectomy

– Injectable polyvalent immunoglobulins: alternative to plasmapheresis

C- against Drugs suitable:

* Neuromuscular Blocking Agents

* Benzodiazepines (Hypnovel)

* General anesthetics (halothane)

* Muscle relaxants and antospasmodiques (dantrolene, baclofen)

* Antibiotics: aminoglycosides +++; colistin; polymyxin B; injectable tetracycline

* Drugs containing the salt of Mg 2+

* Quinine, quinidine, $ hydroquinidine

* D-penicillamine

7- Other causes of myasthenic syndrome:

– Drugs: especially, D-penicillamine can induce autoimmune myasthenia gravis. drugs that blocks the NMJ (curare …)

Lambert-Eaton syndrome: paraneoplastic syndrome myasthiniforme; path is essentially with the lung small cell carcinoma. It is due to presynaptic blockage of neuromuscular transmission (insufficient release of acetylcholine). Ac positive anti-calcium channels in 50% of cases. Muscle deficit improves in the day or after an effort unlike myasthenia gravis. Respect oculomotor and facial motor. The ROT are often abolished.

vegetative disorders.

Botulism: blocking the neuromuscular junction and cholinergic synapse cholinergic parasympathetic system.

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Editor-in-chief of the Medical Actu website; general practitioner graduated from the Faculty of Medicine of Algiers in 2005 currently practicing as a liberal.

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