muscle diseases Flashcards
what are fasciculations
visible, fast, spontaneous twitches
when might fasciculations occur in healthy muscle
stress, caffeine, fatigue
what can fasciculations be a sign of
MND
why do fasciculations occur
denervated muscle becomes hyperexcitable
what is myotonia
failure of muscle to relax after use
how might patients describe myotonia
locking, sticking or cramping of the muscles
what is rhabdomyolysis
where skeletal muscle tissue breaks down and releases the products into the blood
what can cause rhabdomyolysis
prolonged immobility
extremely rigorous exercise
crush injuries
seizures
complications of acute renal failure and DIC
what are the 4 products of rhabdomyolysis that usually end up in the blood
myoglobin
potassium
phosphate
creatine kinase
what is the most immediately dangerous product of rhabdomyolysis and why
potassium
can cause hyperkalaemia - arrhythmias
triad associated with rhabdomyolysis
myalgia, muscle weakness and myoglobinuria
clinical presentation of rhabdomyolysis
muscle aches and pains, oedema, fatigue, confusion
clinical sign of rhabdomyolysis
red-brown urine
investigations in suspected rhabdomyolysis
bloods: CK, U+Es for AKI and hyperkalaemia
urine: myoglobinuria gives red colour, will be positive for blood
ECG
management of rhabdomyolysis
IV fluids
how is spinal muscular atrophy characterised
slowly progressive muscle weakness and atrophy of the limb muscles
+ motor neurone loss in the spinal cord
genetics associated with spinal muscular atrophy
autosomal recessive mutation of SMN1 gene
what is the most common type of spinal muscular atrophy
5q SMA
pathophysiology of spinal muscle atrophy
loss of anterior horn cells
symptoms of spinal muscular atrophy
muscle weakness and wasting : proximal skeletal muscles and respiratory muscles
clinical signs of spinal muscular atrophy
LOWER MOTOR NEURONE WEAKNESS
how can we identify lower motor neurone weakness
hypotonia, flaccid weakness, absent/reduced tendon reflexes, muscle fasciculation, muscle atrophy
what is the main investigation in spinal muscular atrophy
genetic testing
genetics associated with myotonic dystrophy
autosomal dominant inheritance
DMPK gene on chromosome 19
when do patients usually present with myotonic dystrophy
in their 20s
facial features associated with myotonic dystrophy
frontal balding, long, thin face, bilateral ptosis, cataracts
wasting of sternocleidomastoid muscles
internal features of myotonic dystrophy
insulin resistance, metabolic syndrome, cardiomyopathy, arrhythmias, testicular atrophy
hand features of myotonic dystrophy
distal muscle wasting and weakness, slow relaxing grip, percussion myotonia
what is percussion myotonia
thumb flexion on percussion of thenar eminence
investigation for myotonic dystrophy
genetic analysis
raised CK
management of myotonic dystrophy
SUPPORTIVE
cardiac screening, physio
genetic inheritance associated with duchennes and beckers muscular dystrophy
x-linked recessive
pathophysiology of duchennes and beckers
duchennes: absence of dystrophin
beckers: low levels of dystrophin - progresses much slower
what is the role of dystrophin
essential for cell membrane stability
clinical sign associated with duchennes
gowers sign: using arms to compensate weakness in pelvic girdle when getting up off the floor
clinical presentation of muscular dystrophy
delay in motor development
weakness of pelvic and shoulder girdles - onset 3-4yrs
toe walking
exaggerated lumbar lordosis
calf hypertrophy
first line screening for muscular dystrophy
raised creatine kinase
gold standard for diagnosing duchennes and beckers muscular atrophy
genetic testing
what causes botulism
clostridium botulinum
where is clostridium botulinum found and where might it be picked up from
found in soil
contaminated food, contamination of wounds, injection of contaminated street heroin
pathophysiology of botulism
clostridium botulinum is a potent exotoxin
causes inhibition of presynaptic release of ACh
leads to autonomic and motor paralysis
name some clinical uses of botulinum
IM to treat dystonia
botox for wrinkles
clinical presentation of botulism
acute, afebrile descending paralysis
how is botulism detected
toxin in serum, urine, stool, vomit/gastric fluid
management of botulism
early use of antitoxin and treat respiratory failure
what is the most common disorder of the neuromuscular junction
myasthenia gravis
what is the cause of myasthenia gravis
autoimmune
antibodies to ACh receptors
what is a commonality between many patients with myasthenia gravis
thymic hyperplasia / thymoma
what are the 2 groups of patients who usually present with myasthenia gravis
females in their 20s
males in their 50-60s
pathophysiology of myasthenia gravis
auto-antibodies block ACh receptors on the end plate
means inefficient ACh can bind to trigger muscle contraction -> muscle weakness
when do symptoms start in myasthenia gravis (in terms of receptors)
when ACh receptor action is reduced to 30% of normal
clinical presentation of myasthenia gravis
weakness of skeletal muscle - worse throughout the day and after exertion
commonly present with extraocular weakness
clinical presentation of ocular myasthenia gravis
ptosis, diplopia, can’t maintain up-gaze
eye closure initially strong but fatigues after testing
investigations for myasthenia gravis
serum AChR antibodies
CT chest for thymoma
single fibre EMG
management of acute myasthenia gravis
ACh inhibitor - pyridostigmine
IV immunoglobulin or plasma exchange
long term management of myasthenia gravis
steroids
steroid sparing agents
name a steroid sparing agent
azathioprine
what drugs should be avoided as they precipitate myasthenia gravis
beta blockers
gentamicin, macrolides
lithium
benzos
what is Lambert-Eaton syndrome associated with
small cell bronchial carcinoma
pathophysiology of Lambert-Eaton syndrome
antibodies disrupt presynaptic calcium channels
after depolarisation calcium cannot enter neurone meaning less ACh can be released
clinical presentation of Lambert-Eaton syndrome
repeated muscle contractions leads to increased muscle strength
limb-girdle weakness
hyporeflexia
autonomic symptoms: dry mouth, impotence, difficulty weeing
investigation for Lambert-Eaton syndrome
EMG
management of Lambert-Eaton syndrome
management of underlying cancer
potassium channel blockers - 3,4-diaminopyridine
immunosuppression for severe cases - prednisolone + azathioprine
who usually presents with inclusion body myositis
men over 50
characteristic presentation of inclusion body myositis
slow progressive weakness of distal muscles
THUMB SPARING
antibodies associated with inclusion body myositis
anti-cN1A
management of inclusion body myositis
prednisolone
who usually presents with polymyositis
females 40-50
clinical presentation of polymyositis
symmetrical proximal muscle weakness in upper and lower extremities
ILD, dysphagia, myocarditis, raynauds associated
3 clinical signs associated with dermatomyositis
gottrons sign - scaly patches over the knuckles and extensor surfaces of the knees and elbows
shawl sign
helitrope rash
bloods used to identify polymyositis
CK raised !!!
inflammatory markers
autoantibodies
autoantibodies associated with polymyositis and dermatomyositis
anti-jo-1, anti-SRP
what is a definitive test for polymyositis
muscle biopsy
first line management of polymyositis
prednisolone
second line managements for polymyositis
immunosuppression, IVIG, biological therapy
