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    Myasthenia Gravis

    Overview
    Symptoms
    Causes
    Diagnosis
    Treatment Options
    Prevention
    Where To Seek Treatment
    National Neuroscience Institute
    Contributed by Dept of Neurology

    Overview


    Myasthenia Gravis (MG) is a chronic, autoimmune, neuromuscular junction disorder. The neuromuscular junction refers to the tiny cleft between the peripheral nerve endings and the muscle membrane. The nerve endings release the neurotransmitter (acetylcholine), which crosses the junction to bind to receptors on the "distal bank", the muscle membrane. This activates the receptor, which generates a muscle contraction.

    In autoimmune disorder, the body produces antibodies against its own tissue. In MG, antibodies that block, interfere, or destroy the acetylcholine receptors at the neuromuscular junction are made, resulting in easy fatigability and fluctuating muscle weakness.


    Symptoms


    Myasthenia Gravis can affect any skeletal muscle in the body. It can be:

    • Generalised, i.e. affecting muscles that control eyelids, eye movements, facial expression, chewing, swallowing (dysphagia), speech (dysarthria), respiration and limbs.
    • Localised, e.g. in Ocular MG, only the eyelid and eye movement muscles are affected.
    Not all the abovementioned symptoms are present in every patient or at the same time. The two most common symptoms are intermittent drooping of eyelids (ptosis) and double vision (diplopia), which are precipitated by fatigue and relieved by rest.

    Limb weakness usually involves the proximal limb muscles and is worse with repeated activity and at the end of the day. Patients would notice difficulty keeping their arms above their head and getting up from the chair. Some complain of shortness of breath, with exertion or when lying flat.

    The onset of symptoms is usually gradual but it can be sudden, with rapid deterioration of swallowing, breathing and generalised weakness. This is termed myasthenic crisis and it often requires hospitalisation and urgent treatment. Infection and sudden withdrawal of treatment are common triggers.


    Causes

    Myasthenia Gravis affects all ethnic groups and both genders. It is more common in young adult women (under 40 years old) and older men (over 60 years old) but can affect all age groups. It can also occur in the newborn (usually from a myasthenic mother who passes the antibodies to the fetus) and children. In adults, MG is usually not hereditary. It is not contagious.


    Diagnosis


    Your doctor will take a detailed medical history from you and do a thorough neurological examination. There is no single investigation that can absolutely exclude MG.

    Some investigations for MG include:

    Blood test
    This is the simplest and most specific investigation but is only 90% sensitive. it detects the antibodies produced against the acetylcholine receptors at the neuromuscular junction. It takes about few weeks for the result to be available. 

    Repetitive Nerve Stimulation
    This test is easy to perform but no very sensitive. It is an electrical test which involves giving small but tolerable electric shocks to nerves in the face, neck and forearm in quick secessions and recording the nerve responses.

    Singer Fiber Electromyography (SFEMG)
    This is a more sensitive electrical test to diagnose MG. This test involves inserting a small needle electrode, into the forehead or a forearm muscle to record the differences in response time between a pair of muscle fibers. This test is technically demanding and takes about an hour to perform.

    10% of patients with MG have an associated tumour of the thymus gland (thymoma). Hence, your doctor will order a CT scan of the chest to exclude a thymoma.  


    Treatment Options


    Patients with severe, acute and generalised symptoms (especially involving swallowing and respiration) will usually require hospitalisation for urgent treatment. They can be given a course of intravenous immune globulin (IVIG) or few cycles of plasma exchange. IVIG is derived from pooled donor blood and contains normal antibodies that will help to temporarily counteract the abnormal antibodies. Plasmapheresis is a procedure where the abnormal antibodies are filtered out of the body by a machine.

    Long-term treatment is achieved by oral medications. Pyridostigmine prevents degradation of acetylcholine in the neuromuscular junction. It is usually given to improve weakness.

    Most patients will require immunosuppression to control the disease. Steroids (e.g. Prednisolone) are the mainstay of treatment. Initial treatment requires fairly high dose of this drug. Once the disease is under control, the dosage will be gradually reduced to the minimum. Side effects of steroids include weight gain, fluid retention, acne, development of hypertension, diabetes mellitus, osteoporosis and hip fractures. However, most of these adverse events can be minimised with stringent diet modifications and medications like bisphosphonates.

    Your doctor may also prescribe another drug such as azathioprine that will help to reduce the amount of steroids required. This drug takes a while to take effect. Patients on immunosuppressants will require frequent blood checks (full blood count and liver function tests) at the start of treatment and at regular intervals. No medications should be stopped abruptly.

    Surgical removal of the thymus gland (thymectomy) is mandatory if a thymoma is seen on the CT chest. Its value is less clear when there is no obvious enlargement although most authorities believe it would improve the long-term control of MG and would consider it in patients less than 60 years old.


    Prevention


    Living with Myasthenia Gravis

    Although there is no quick cure for Myasthenia Gravis, the outlook for most patients is good. With proper treatment and adequate control, remission may be achieved in many patients. Most patients can expect to live normal or near normal lives with no decrease in life expectancy.
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