Myasthenia Gravis

Definition chronic autoimmune neuromuscular disease characterized by varios degrees of weakness of skeletal muscle . affects people of age more common in women younger than 40 and men older 60 hereditary disorder & Death may occur due to respiratory paralysis

Manifestation dropping eye lids , walking problems & change in facial expression : The hallmark of myasthenia gravis is fatigability. Muscles become progressively weaker during periods of activity and improve after periods of rest. Muscles that control eye and eyelid movement, facial expressions, chewing, talking, and swallowing are especially susceptible. The muscles that control breathing and neck and limb movements can also be affected. Often, the physical examination yields results within normal limits The onset of the disorder can be sudden. Often symptoms are intermittent. The diagnosis of myasthenia gravis may be delayed if the symptoms are subtle or variable.

Manifestation shortness in breath : many muscles “sometimes including those that control breathing” are affected. Symptoms, which vary in type and severity, may include asymmetrical ptosis (a drooping of one or both eyelids), diplopia (double vision) due to weakness of the muscles that control eye movements, an unstable or waddling gait, weakness in arms, hands, fingers, legs, and neck, a change in facial expression, dysphagia (difficulty in swallowing), shortness of breath and dysarthria (impaired speech, often nasal due to weakness of the velar muscles).

Note : In myasthenic crisis a paralysis of the respiratory muscles occurs, necessitating assisted ventilation to sustain life. In patients whose respiratory muscles are already weak, crises may be triggered by infection, fever, an adverse reaction to medication, or emotional stress. Myasthenia does not directly affect the heart muscle.

Causes Myasthenia gravis is caused by a defect in the transmission of nerve impulses to muscles.  Normal transmission neuromuscular : It occurs when normal communication between the nerve and muscle is interrupted at the neuromuscular junction “the place where nerve cells connect with the muscles they control” . Normally when impulses travel down the nerve, the nerve endings release a neurotransmitter substance called acetylcholine. Acetylcholine travels from the neuromuscular junction and binds to acetylcholine receptors which are activated and generate a muscle contraction.

Abnormal neuromuscular transmission :  Antibodies block or destroy the receptors for acetylcholine at the neuromuscular junction, which prevents the muscle contraction from occurring. These antibodies are produced by the body's own immune system.  Myasthenia gravis is an autoimmune disease because the immune system “which normally protects the body from foreign organisms “ mistakenly attacks itself

Normal neuromuscular jun. Myasthenia gravis

Medication Acetyle-cholinesterase inhibitors (neostigmine) Immuno suppressive drugs  Immuno modulatory therapy  Surgery “ thymectomy “

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