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muscular disease; myopathy
Etiology:
1) muscular dystrophies
a) Duchenne muscular dystrophy
b) Becker muscular dystrophy
c) limb-girdle muscular dystrophy
d) myotonic dystrophy
2) metabolic myopathies
a) acid maltase deficiency
b) McArdle disease
3) mitochondrial myopathies
a) Kearns-Sayre syndrome
b) Leigh syndrome
c) MERRF, MELAS, MNGIE
4) congenital myopathies
- nemaline myopathy
5) neurologic disease & neuromuscular disorders
a) amyotrophic lateral sclerosis
b) myasthenia gravis
c) Guillain-Barre syndrome
d) stroke
e) multiple sclerosis
6) inflammatory myopathies (myositis)
a) dermatomyositis
b) polymyositis
c) inclusion body myositis
7) connective tissue disease
a) systemic lupus erythematosus
b) mixed connective tissue disease
c) scleroderma
8) endocrine disease
a) hypothyroidism
b) Addison's disease
c) vitamin D deficiency
9) infections
a) bacterial infection
- Lyme disease
- Listeria monocytogenes (non-bloody diarrhea, encephalopathy, dairy)
- pyomyositis
b) viral infection
- influenza
- HIV1 infection
- hepatitis B infection
- hepatitis C infection
c) parasitic infection
- toxoplasmosis
- trichinosis
10) drug induced myopathy
a) anti-hyperlipidemic agents
- immune-mediated necrotizing myopathy (statin myopathy)
- increased risk when combined with fibrate
- ezetimibe
- nutriceuticals (red yeast rice)
b) antiviral agents
1] antiretroviral agents
- zidovudine, HAART
2] interferons
c) emetics
- emetine, ipecac
d) immunosuppressants
- glucocorticoids
- leflunomide
- TNF-alpha inhibitors
- adalimumab
e) microtubule inhibitors
- colchicine
- vincristine
f) antimalarial agents
- chloroquine
- hydroxychloroquine
g) alcoholism
Clinical manifestations:
- generally painless
- painful myopathy should prompt search for metabolic, toxic & infectious causes [1]
- progressive symmetric weakness of proximal muscles, generally of limbs
- no sensory loss
- normal reflexes
Laboratory:
- elevated serum creatine kinase
- useful for monitoring disease activity & response to treatment
- levels may be normal in patients with slowly progressive myopathy
- always check serum TSH when evaluating myopathy
- genetic testing as indicated
Special laboratory:
- electromyography confirms myopathic changes [1]
- low amplitude, short duration, & polyphasic motor unit potentials [1]
- muscle biopsy
Differential diagnosis:
- myopathy of hypothyroidism
- diffuse myalgia, proximal muscle weakness, elevation of serum creatine kinase, delayed relaxation of deep tendon reflex
- myopathy of hyperthyroidism
- brisk reflexes, fasciculations, opthalmoplegia
- myopathy of vitamin D deficiency
- proximal muscle weakness, myalgia, fatigue, osteomalacia-related bone pain
- myopathy of glucocorticoids
- proximal muscle weakness, myalgia, normal serum creatine kinase, normal EMG
- statin myopathy*
- subacute toxic myopathy, rhabdomyolysis
- risk of myopathy increased with co-administration of fibrate & CYP3A4 inhibitor
- myotonic dystrophy
- myotonia (delayed handgrip release), distal muscle weakness
* lipophilic statins (atorvastatin, simvastatin, lovastatin) more likely to cause statin myopathy than hydrophilic statins (rosuvastatin, pravastatin, fluvastatin)
Related
age-associated changes in skeletal muscle
skeletal muscle (voluntary muscle)
Specific
eventration of diaphragm
genetic disease of muscle (inherited myopathy)
hyperCKemia (elevated serum creatine phosphokinase)
malignant hyperthermia/hyperthermia of anesthesia
metabolic myopathy
muscle atrophy (amyotrophy)
myasthenic syndrome (congenital myasthenic syndrome, CMS)
myofascial pain syndrome
myofibrillar myopathy
myositis (inflammatory myopathy)
myositis ossificans
myotonic disorder
neurogenic scapuloperoneal syndrome Kaeser type (Kaeser syndrome)
neuromuscular disease; myoneural disease
rhabdomyolysis
rippling muscle disease
sarcopenia
toxic myopathy; drug-induced myopathy
General
musculoskeletal disease/disorder
References
- Medical Knowledge Self Assessment Program (MKSAP) 11, 16, 17, 18.
American College of Physicians, Philadelphia 1998, 2012, 2015, 2018
- Medical Knowledge Self Assessment Program (MKSAP) 19
Board Basics. An Enhancement to MKSAP19.
American College of Physicians, Philadelphia 2022