Myasthenia Gravis Flashcards
what is the general presentation of myasthenia Gravis?
Fatigable muscles (muscle weakness worsening after periods of activity and improves after periods of rest) and norm reflexes + no sensory symp – associated with thymic hyperplasia(and thymomas)
RESTRICTIVE PATTERN OF LUNG DISEASE
Define myasthenia Gravis?
autoimmune disease affecting neuromusular junction producing weakness in skeletal muscles
define myasthenia gravis?
autoimmune disease affecting the post synpatic membrane at the neuromuscular junction producing weakness in skeletal muscles
outlinethe aetiology of myasthenia gravis?
antibodies against nicotinic acetylcholine receptor which interferes with neuromuscular transmission via depletion of post- synaptic receptor sites
what is lamberton Eaton syndrome?
paraneoplastic subtype of myasthenia gravis caused by autoantibodies against pre-synaptic calcium channels leading to impairement of acetyl choline release
can be paraneoplastic ( from small cell lung cancer) or autoimmune
what are the symptoms and signs of lambert- eaton syndrome
what conditions if myasthenia gravis associated with?
associated with other autoimmune conditions ->PERNICIOUS ANAEMIA AND THYMOMA
associated with thymus hyperplasia
summarise the epidemiology of myasthenia gravis?
Prevalence: 8-9/100,000
More common in FEMALES under 50
More common in MALES after 50
what are the presenting symptoms of myasthenia gravis?
weakness that worsens with repetitive use or towards the end of the day- FATIGUABILITY
order of muscle weakness extraocular -> bulbar-> face-> neck-> limb girdle-> trunk
ocular symptoms
- ptosis
- diplopia
Bulbar symptoms
- facial paresis ( myasthenic snarl)
- dysarthria -disturbed hypernasal speech
- dysphagia-difficulties chewing and swallowing
Proximal limb weakness
- difficult to get out of chairs or climb stairs
how is the fatigue from lamberton-eaton syndrome different to myasthenia gravis?
lamberton-eaton syndrome=muscle weakness improves after repeated use
myasthenia gravis= weakness worsens on activity ( fatigue) and improves on rest
what is the order of muscle weakness in myasthenia gravis?
extraocular -> bulbar -> face -> neck -> limb girdle-> trunk
what are the signs of myasthenia gravis?
May be generalised (affecting many muscle groups)
Eye Signs
- Ptosis
- Complex ophthalmoplegia
- Check for ocular fatigue by asking the patient to sustain an upward gaze for 1 min and watch the progressive ptosis that develops
Ice on Eyes Test
- Placing ice packs on closed eyelids for 2 mins can improve neuromuscular transmission and reduce ptosis
Bulbar Signs
- Reading aloud may cause dysarthria or nasal speech – on counting to 50, the voice fades
Limbs
- Test the power of a muscle before and after repeated use of the muscle
- Tendon reflexes are normal
Tensilon Test
what is the tensilon test?
administering a very short-acting acetylcholinesterase inhibitor to diagnose myasthenia gravis by demonstrating by a rapid improvement in muscle weakness
what are the signs on Lamberton-Eaton syndrome on physical examination?
gait difficulty before eye signs, autonomic involvement (dry eyes, constipation), hyporeflexia and weakness that improves after exercise – depressed tendon reflexes are because less transmitter is released but reflexes may increase after maximum voluntary contractions due to build up of transmitter in the synaptic cleft.
what are the investigations for myasthenia Gravis?
CK - exclude myopathies
Serum acetylcholine receptor antibody (positive in 90%)
If seronegative, look for MUSK antibodies (multiple specific tyrosine kinase)
TFTs (it is associated with hyperthyroidism)
Serial PFTs
- MG crisis: low FVC and NIF (negative inspiratory force) - only is SOB in history
what are the investigations for lamberton eaton syndrome?
Anti-voltage gated calcium channel antibody (in Lambert-Eaton syndrome)
autoantibodies interfere with the normal influx of pre-synaptic calcium that allows for release of acetylcholin->results in less post-synaptic stimulation.
Repetitive stimulation allows for acetylcholine levels to reach sufficient levels to improve muscle contraction, which explains why patients’ weakness briefly improves with repetitive testing.
what investigations should you consider for laberton eaton syndrome?
Nerve Conduction Study
- Repetitive stimulation shows decrements of muscle action potential
EMG
CT Thorax/CXR - visualise thymoma in the mediastinum or lung malignancies – found in 20% of MG pati
