II. Definitions

  1. Myopathy
    1. Non-cancer disorder affecting skeletal or smooth muscle
  2. Myositis
    1. Inflammation of skeletal muscles

III. Findings

  1. Suggestive of Myopathy
    1. Gradual onset of symmetric weakness
    2. Proximal weakness
      1. Difficulty combing hair
      2. Difficulty walking up stairs
    3. Neck Flexion weaker than neck extension
    4. Deep Tendon Reflexes preserved
  2. Suggestive of alternative diagnosis (i.e. Neuropathy)
    1. Sudden onset of asymmetric weakness
    2. Paresthesias in extremities
    3. Bowel dysfunction (e.g. Stool Incontinence)
    4. Bladder dysfunction (e.g. Urinary Incontinence)
    5. Distal weakness suggests Neuropathy
      1. Except in Guillain-Barre, Myotonic Dystrophy
    6. Deep Tendon Reflexes lost

IV. History: Direct to specific Myopathy

  1. Family History of Myopathy: Muscular Dystrophy
  2. Difficult swallowing: Polymyositis
  3. Weakness varies and includes eyes: Myasthenia Gravis
  4. Age of onset
    1. Age <30: Muscular Dystrophy

V. Labs

  1. Creatine Phosphokinase (CPK) increased
  2. Aspartate Aminotransferase (AST) may be increased
  3. Aldolase may be increased
  4. Lactate Dehydrogenase (LDH) may be increased

VI. Diagnostics

  1. Electromyogram (EMG)
  2. Nerve Conduction Studies (NCS)
  3. Muscle biopsy

VII. Causes

  1. See Myopathy Causes
  2. See Polymyositis Differential Diagnosis
  3. See Medication Causes of Myositis
  4. See Muscular Dystrophy
  5. See Muscle Weakness in Children (Pediatric Neuromuscular Disorders)
  6. See Acute Motor Weakness Causes
    1. Critical to rule-out emergent causes
  7. Infectious Myositis
    1. Viral Myositis
      1. Influenza (esp. affecting calf muscles, with "Charlie-Chaplain shuffle" with Out-toeing)
    2. Bacterial Myositis (pyomyositis)
      1. Focal infection (esp. upper thigh or deep Pelvis)
      2. Gram Positive infection (esp. Staphylococcus) in most cases
      3. May be associated with underlying Osteomyelitis
  8. Treatable myopathies
    1. Thyroid Myopathy (Hypothyroidism, Hyperthyroidism)
    2. Polymyositis
    3. Critical Illness Myopathy
    4. Drug Induced Myositis
      1. Alcoholic Myopathy
      2. Statin-Induced Myopathy
      3. Steroid Myopathy
    5. Hypokalemic Periodic Paralysis
    6. Polymyalgia Rheumatica
    7. Myasthenia Gravis
    8. Eaton-Lambert Syndrome

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Ontology: Myositis (C0027121)

Definition (MSH) Inflammation of a muscle or muscle tissue.
Definition (MSHCZE) Zánět svalu nebo svalové tkáně. R
Definition (MEDLINEPLUS)

Myositis means inflammation of the muscles that you use to move your body. An injury, infection, or autoimmune disease can cause it. Two specific kinds are polymyositis and dermatomyositis. Polymyositis causes muscle weakness, usually in the muscles closest to the trunk of your body. Dermatomyositis causes muscle weakness, plus a skin rash.

Other symptoms of myositis may include

  • Fatigue after walking or standing
  • Tripping or falling
  • Trouble swallowing or breathing

Doctors may use a physical exam, lab tests, imaging tests and a muscle biopsy to diagnose myositis. There is no cure for these diseases, but you can treat the symptoms. Polymyositis and dermatomyositis are first treated with high doses of a corticosteroid. Other options include medications, physical therapy, exercise, heat therapy, assistive devices, and rest.

NIH: National Institute of Neurological Disorders and Stroke

Definition (SCTSPA) Inflamación del músculo esquelético; no incluye la inflamación del músculo cardíaco
Definition (SNOMEDCT_US) Inflammation of skeletal muscle, not including inflammation of cardiac muscle
Definition (NCI_CTCAE) A disorder characterized by inflammation involving the skeletal muscles.
Definition (NCI) An inflammatory process affecting the skeletal muscles. Causes include infections, injuries, and autoimmune disorders.
Definition (CSP) inflammation of skeletal muscle.
Concepts Disease or Syndrome (T047)
MSH D009220
ICD10 M60 , M60.9, G72.49
SnomedCT 203110007, 268108002, 26889001, 128496001
English Myositides, Myositis unspecified, Myositis, unspecified, MYOSITIS, INFLAMM MUSCLE DIS, MUSCLE DIS INFLAMM, INFLAMM MYOPATHY, MYOPATHY INFLAMM, inflammatory myopathy, inflammatory myopathy (diagnosis), Inflammatory Muscle Disease, Inflammatory Muscle Diseases, Muscle Disease, Inflammatory, Muscle Diseases, Inflammatory, Inflammatory Myopathies, Inflammatory Myopathy, Myopathies, Inflammatory, Myopathy, Inflammatory, Inflammatory myopathy NOS, Myositis [Disease/Finding], Myositis, Unspecified myositis, inflammation of the skeletal muscle, inflammatory muscle disease, inflammatory muscle diseases, myositis nos, Inflammation;muscle(s), muscle inflammation, inflammatory myopathies, myositis (diagnosis), Myositis NOS, Myositis unspecified (disorder), Inflammatory disorder of muscle (disorder), Inflammatory disorder of muscle, Inflammatory myopathy, Myositis (disorder), myositis, disease (or disorder); muscle, inflammatory, inflammation; muscle, inflammatory; myopathy, muscle; disease, inflammatory, muscle; inflammation, myopathy; inflammatory, Myositis, NOS, Muscle inflammation, inflammation of the muscle(s)
French MYOSITE, Inflammation musculaire, Myosite, Maladies inflammatoires des muscles, Myopathie inflammatoire
Portuguese MIOSITE, Inflamação muscular, Miosite, Miopatia Inflamatória
Spanish MIOSITIS, Inflamación muscular, miositis, no especificada, miositis, no especificada (trastorno), miopatía inflamatoria (trastorno), miopatía inflamatoria, miositis (trastorno), miositis, trastorno muscular inflamatorio, Miositis, Miopatía Inflamatoria
German MYOSITIS, Muskelentzuendung, Myositis, nicht naeher bezeichnet, Myositis, Entzündliche Myopathie, Muskelentzündung
Dutch spierontsteking, aandoening; spier, inflammatoir, inflammatoir; myopathie, myopathie; inflammatoir, ontsteking; spier, spier; aandoening, inflammatoir, spier; ontsteking, Myositis, niet gespecificeerd, myositis, Inflammatoire myopathie, Myositis
Italian Infiammazione muscolare, Malattie infiammatorie dei muscoli, Miopatie infiammatorie, Miosite
Japanese 筋肉の炎症, キンエン, キンニクノエンショウ, 筋炎, 筋肉炎
Swedish Muskelinflammation
Czech myozitida, zánětlivé nemoci svalů, svaly - zánět, zánětlivá myopatie, Zánět svalu, Myozitida, zánět svalu, zánětlivé myopatie
Finnish Myosiitti
Russian MIOZIT, МИОЗИТ
Korean 근육염, 상세불명의 근육염
Croatian UPALA MIŠIĆA, MIOZITIS
Polish Zapalenie mięśni eozynofilowe, Zapalenie mięśni
Hungarian Myositis, Izomgyulladás
Norwegian Inflammatorisk myopati, Myositt, Muskelsykdommer, inflammatorisk, Myopati, inflammatorisk, Inflammatoriske muskelsykdommer