Muscle Disorders Flashcards
What are the 5 questions you should include in your history for a patient with a muscle disease?
- What are the symptoms?
- What is the temporal course?
- Is there a family history of muscle disease?
- Are there provocative factors?
- Is there a pattern for symptoms?
- Are other symptoms involved?
Wha is the most common pattern of acquired muscle weakness?
Proximal
What are the “negative” symptoms of muscle disease?
weakness
fatigue
atrophy
exercise intolerance
What are the “positive” symptoms of muscle disease (7) ?
myalgia
cramps
hypertrophy
contractures
stiffness
myotonia
myoglobinuria
What are the 3 components to a muscle examination? Describe the specific aspects of each.
- Look
- atrophy, pseudohypertrophy, fasciculation
- Touch
- palpate for tenderness, check muscle tone
- Engage
- test power (0-5)
- weakness due to pain, fatigue, decreased effort?
- test power (0-5)
What special test is being performed in the provided image?
What are 2 other tests for the same pathology?
Percussion Myotonia
percuss thenar emminence & there is an abnormal contraction of abductor pollicis brevis
Can also test: have them grip hand (+ = delay in opening); close eyes (+ = delay in opening)
Percussion myotonia is seen in what two types of diseases?
myotonic dystrophy & channelopathies
What change in reflexes do you see in muscle disease?
reflexes are never increased
The presence of what additional symptoms indicate that a primary myopathy is unlikely?
sensory, bowel, or bladder symptoms
What is the most important diagnostic test to perform when muscle disease is suspected?
Creatinine phosphokinase
Is CPK usually elevated or depressed in muscle disease?
elevated
CPK is markedly elevated in what 4 muscle diseases?
duschenne/Becker dystrophy
inflammatory myopathies
hypothyroid myopathy
rhabdomyolysis
CPK is low/normal in what 4 muscle diseases?
dermatomyositis
steroid-induced myopathy
thyrotoxic myopathy
hyperparathyroidism
What are the 4 major causes of Rhabdomyolysis?
neuroleptic malignant syndrome - antipsychotics
malignant hyperthermia- anesthesia
crush or blast injuries; muscle ischemia
statins (rare)
What thyroid conditions can lead to acquired muscle diseases & what is the general CK associated with each?
- Hypothyroidism- myxedema (CK 10-100x)
- Hyperthyroidism- thyrotoxic myopathy (CK low/normal)
What muscle issues do you see in hypoparathyroidism? Hyperparathyroidism?
- Hypoparathyroidism: tetany
- Hyperparathyroidism: proximal myopathy
How will corticosteroid induced myopathy show up on biopsy?
type 2 fiber atrophy
What exogenous steroid dosing should you start to be concerned about induced myopathy?
>30mg/day x weeks/months
What is the most common type of electrolyte imbalance that can lead to myopathy?
hypokalemia
If a person is on a statin, what additional medications drastically increases the chances of developing rhabdomyolysis?
calcium channel blocker
cyclosporine
gemfibrozil
Why do statins cause myopathy?
they decrease mevalonate - a terpene / steroid precursor
10% of patients on statins experience what muscle-related side effects?
myalgia/cramps
rhabdomyolysis is RARE (0.1%)
What genetic factors predispose individuals to statin-induced muscle disease?
- 2% pop is homozygous for SNP
- rare autoimmune HMG-CoA Reductase
What are the 4 substance that most commonly cause toxic myopathies?
EtOH, cocaine, colchicine, penicillamine
Antipsychotics can induce what syndrome that includes muscle disease? What are the symptoms of this syndrome?
Neuroleptic malignant syndrome
fever, muscular rigidity, rhabdomyolysis, delirium, death (5-10%)
What is the cause of Malignant Hyperthermia?
autosomal dominant ryanodine receptor mutation (chromosome 19) - exposure to depolarizing muscle relaxants (succinylcholine) or inhaled anesthetics (halothane, sevoflurane, desflurane)
this causes increased calcium release from sarcoplasmic reticulum
What are the symptoms seen in Malignant Hyperthermia?
muscle rigidity, hyperthermia, cardiac arrhythmias, CK elevation, metabolic acidosis, myoglobinuria
What is the treatment for malignant hyperthermia?
dantrolene
prevents release of calcium
What demographics of people are affected by criticla illness myopathy?
patients ventilated in ICU who are exposed to prolonged disuse and neuromuscular blocking agents
What are the symptoms of critical illness myopathy? muscle biopsy?
proximal flaccid weakness (usually not severe)
CK elevation
biopsy: loss of reactivity for myosin ATPase activity in type 1 fibers more than type 2 fibers
How can you tell the difference between steroid-induced myopathy vs critical illness myopathy:
biopsy?
causative drug?
distribution?
-
Steroid-induced myopathy
- biopsy: type 2 fiber atrophy
- causative drug: prednisone > 30mg/day
- distribution: spares bulbar/facial and distal muscles
-
Critical Illness Myopathy
- biopsy: type 1 atrophy > type 2 atrophy
- causative drug: neuromuscular blocking agents + disuse
- distribution: proximal
What viral infections can cause localized myositis?
influenza A & B, HIV
What bacterial infections can cause localized myositis?
streprococci, MRSA
What parasitic infections can cause localized myositis?
trichinosis
cysticercosis
toxoplasmosis
What is the classic clinical picture of a patient with dermatomyositis?
female with subacute, symmetric, proximal > distal weakness
(dysphasia/dysphagia, polyarthritis, interstitial lung disease)
often associated with cancer or other autoimmune conditions
What elevated lab values would you expect to see in a patient with dermatomyositis? Antibodies?
CK
LDH
aminotransferase
30% (+) myositis antibodies
Dermatomyositis is what type of condition?
microangiopathy directed against intramuscular blood vessels
What type of findings are seen in a muscle biopsy of a patient with dermatomyositis?
perifascicular atrophy
vasculitic changes