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

 

Polymyositis

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

Causes

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)

                  

Polymyositis

 

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

 

Polymyositis:

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)

Advice

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

 

 

Polymyositis:

 

Treatment focuses on improving muscle strength and functionality

 

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

 

Electromyography

 

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)

MISCONCEPTIONS
  • 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

Statistics

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

 

Polymyositis:

 

More common in the black population

 

US prevalence range: 0.5-8.4 per million