Myasthenia gravis and Polymyositis

Myasthenia gravis

A rare autoimmune disorder in which communication between nerves and muscles is disrupted. It is generally characterized by weakness and fatigue in muscles that are normally under voluntary control.


Clinical classification:

Class I – “initial” form, ocular muscle weakness

Class II – mild weakness in other muscles than ocular ones: a) affecting limb and axial muscles; b) affecting oropharyngeal and/or respiratory muscles (+/- initial form)

Class III – moderate weakness in other muscles than ocular (+/- initial form)

Class IV – severe weakness in muscles other than ocular (+/- initial form)

Class V – inability to breathe, intubation needed



An inflammatory disease that causes gradual and symmetrical muscle weakening. It affects adults of 30 to 50 years old.


Myasthenia gravis


Antibodies – the immune system generates antibodies that block/destroy the receptor sites for a certain neurotransmitter (acetylcholine); the sites are placed at the nerve-muscular junction and as they are attacked by antibodies, the signals the muscles receive decrease and weakness appears


Antibodies can also interfere with a muscle-specific receptor protein, tyrosine kinase, that helps in forming the muscle-joint junction


Enlarged thymus gland or tumors on this gland – this appears to be the gland that commands the antibodies that block acetylcholine


Antibody negative myasthenia gravis (the antibodies attack a protein, lipoprotein-related protein 4)


Genetic factors: myasthenia passed to the infant from the mother – neonatal myasthenia gravis (can be treated in two months)

                             –congenital myasthenic syndrome (rare hereditary form)




Idiopathic (exact cause is unknown)


Possibly caused by “misled” antibodies (the immune system mistakenly attacks healthy body tissues)

Symptoms and signs

Myasthenia gravis


First signs involve eye problems

Ptosis – drooping of the eyelid(s)

Diplopia – double vision

Limited facial expression

Altered speaking

Difficulty swallowing and chewing

Weakness in neck, arms and legs

Difficulty in movement coordination



Weakness in the muscles of the hips, thighs, neck, shoulders and upper arms

Difficulty swallowing

Difficulty in climbing or lifting objects

Calcium deposits in the muscle or connective tissue (in late stage)


Myasthenia gravis:


The doctor will assess symptoms, medical history and do a physical examination


Neurological examination to check reflexes, coordination, balance, muscle strength and tone, sense of touch and sight


Blood tests – to see abnormal antibodies


Edrophonium test – a chemical is injected and may offer temporary improvement in muscle strength


Ice pack test – to see improvement in eyelids


Repetitive nerve stimulation – the nerve’s ability to transmit signals is checked


Single-fiber electromyography – electrical activity between nerves and brain is measured


Imaging tests – CTs or MRIs are used to see abnormalities in the thymus gland or tumors


Treatment consists in managing symptoms


Medication: cholinesterase inhibitors (to improve communication between nerve and muscle), corticosteroids (limit antibody production), immunosuppressant (alter immune system response)


Therapy: plasmapheresis (similar to dialysis – to remove the abnormal antibodies), intravenous immunoglobulin (introduces normal antibodies in the system)


Surgery: video-assisted thymectomy (to remove tumors of the thymus gland), robot-assisted thymectomy





Treatment focuses on improving muscle strength and functionality


Blood tests: muscle enzymes (increased levels of creatine kinase and aldolase suggest muscle damage), antibodies




MRI (magnetic resonance imaging) – to observe inflammation range and severity


Muscle biopsy (to check for inflammation, necrosis – dead tissue, degenerated muscle fiber)


Medication: corticosteroids, corticosteroid-sparing agents (combined with corticosteroid treatment)


Intravenous immunoglobulin


Therapies: physical therapy to improve muscle strength and mobility, speech therapy


Diet changes (needed as the disease progresses due to chewing and swallowing difficulties)

  • Myasthenia gravis is just an excuse for laziness


    A more vigorous exercise routine will cure the problem


    Recovery is just a matter of wanting to get better


    Food supplements and medication can “cure” muscle weakness


Myasthenia gravis


Most common primary disorder of neuromuscular transmission


Prevalence in the US: 14-20 cases/100,000 people


Approximately 36,000-60,000 cases in the US


Average onset age for women: 28 years and for males: 42 years




More common in the black population


US prevalence range: 0.5-8.4 per million