Differential diagnoses myositis and dermatomyositis 5/5 (3)

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Differential diagnosis

There are many diseases similar to myositis and should be considered in the medical investigation. Also, when treatment does not work as expected, similar conditions should be carefully considered.

  • Amyloid myopathy
    • Subcutaneous changes
    • Proteinuria
    • Typical biopsy (dye with Congo)
  • Diabetic amyotrophy and diabetic muscle infarction
    • Acute, asymmetric onset of focal pain and weakness in thighs.
    • Often weight loss
    • EMG differs from myositis
  • Electrolyte shortage
    • Hypo-kalaemia
    • Hypo-kalsemi
    • Hypo-magnetite semi
  • HIV infection
    • Chronic weight and power loss
    • Clinical picture with CK increase (inflammatory myopathy) as in myositis
    • HIV test
    • CD4 T cells do not correlate well with myopathy symptoms
  • Kennedy disease (Spinal and bulbar muscular atrophy, SBMA)
    • Weakened force and symmetrical muscle atrophy in proximal muscles. Creatine kinase (CK) is moderately elevated. Men in 40-50 years of age. Reduced androgen sensitivity with gynecomastia, atrophy tested and decreased libido. Fasciculations in facial muscles. Speech and swallowing difficulties
    • Separated from myositis by clinical picture (facial muscles, gynecomastia, EMG and muscle biopsy)
  • Lambert-Eaton syndrome
    • Myasthenia-like
    • Paraneoplastic Syndrome
    • Not eye muscle affection
    • Antibody against voltage-gated calcium channel (VGCC)
    • EMG discovery
  • Macro-CK
    • Macro Enzymes are normal enzymes (or isoenzymes) that bind either to immunoglobulins (IgG) = Type 1 or lipoproteins and other substances (Type 2) and thus accumulate in serum. They are not free enzymes, but cause falsely elevated CK measurements.
    • Macro-CK is most commonly seen in people over 60 years
    • Macro-CK may be present with or without associated disease, including chronic liver disease and malignancy
  • Muscular Dystrophy (Hereditary progressive muscle diseases)
    • Should always be considered by chronic muscular disease
  • Myastenia gravis
    • Increased physical muscular fatigue
    • Often in facial muscles, including eyes
    • Normal CK
    • EMG is characteristic
    • Anti-acetylcholine antibodies
  • Myoclonic Epilepsy with Ragged Red Fibers»(MERRF)
    • "Ragged Red Fibers" are congested diseased mitochondria in tissue samples (biopsy)
    • Low body height, hearing loss, lactate acidosis, intolerance to physical exercise
  • Parkinson's disease
    • Tremor

Diagnosis of elevated serum CK

  • If creatine kinase (CK) is below 1000, the sample is repeated without prior physical activity
    • Elevated CK levels are expected to be halved by approx. every 24-36 hours if the triggering cause is removed. Normalization within 3-5 days is expected
  • Trauma, physical overload, cramps, infections, injections, metabolic myopathy. At very high CK consider: Rhabdomyolysis
  • Troponin T (CTnT) is not specific to the heart muscle and often exceeds the skeletal muscle involvement. Troponin I (cTnI), on the other hand, is more myocardial specific.
  • Among ethnic black Africans, CK is up to 70% higher than in whites (reference: Brewster CM, 2012)


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