ICD-10 codes

• Polymyositis M33.2
• Dermatomyositis M33.1
• Juvenil Dermatomyositis M33.0
• Antisynthetase syndrome M35.8 + J99.1
• Inclusion body myositis M60.8
• Myositis related to cancer M36.0

 The diagnosis is based on

• Disease history
  • Muscles
  • Skin
  • Lungs
• Investigation findings (including CK)
• Exclude another disease (differential diagnoses)

Disease history / Symptoms

• First-degree family (parents, siblings or children) with muscular disease: Exclusion Muscular Dystrophy?
• Debut of muscle symptoms
  • Time and what muscle groups: proximal / distal, thigh, neck
  • Previous new medication with statins, anabolic steroids, drugs or something else?

* (Star) indicates data included in classification criteria:

Muscles

• * Symmetrical weakness in proximal muscle groups (classical)
  • Often distal muscles at Inclusion body myositis
  • Reduced strength
    • Walking function affected (stairs, hills)
• Atrophy symmetrically, proximal / distal in muscles
• Swallowing Function:
  • Hard to swallow? (Aspiration?)
• Signs of reduced heart muscle function? (myocarditis)
• Muscle pain (at 40%)
• * Elevated CK, maximum CK value (400-30.000?)

• Accompanying symptoms
  • * Skin (rash: Dermatomyositis)
  • Edema
    • Subcutaneous swelling of high disease activity
  • Dysphagia (esophagus infection)
    • Hard to swallow solid food
    • Aspiration
  • Lungs (Antisynthetase syndrome)
    • Dry cough
    • Dyspnoea by strain
  • Joints (Arthritis)
    • Deformity in Tumors (90 - 90 Deformity)
    • Flex in PIP joints (fingers) at Inclusion body myositis
• Possible triggering factors
  • Drug Consumption (statins, drugs / heroin)
  • Alcohol abuse

Immunosuppressive treatment

• Prednisolone, MTX, Mycophenolate (CellCept), Imurel, Ciclosporin, Tacrolimus, Rituximab, Cyclophosphamide, Immunoglobulin.
• Statins

Stimulants

• Tobacco (yes, not, previously)
• Alcohol
• Other drugs (Cocaine with more)

Investigations / Investigation

• Clinical examination

Muscles

• Muscle atrophy
  • Proximal (thighs, upper arms)
  • Distal (underarms) adds to the inclusion body myositite

• Muscle strength
  • Raising from squatting without help?
  • Getting up from chair without support?
  • Handshake
  • Hard to raise the arms over the head?
  • The neck / head is hard to keep up?

Skin

• Erythrodermi (Dermatomyositis)
• Subcutaneous edema (includes face), in high disease activity
• * Gottron's sign and papler
  • Red-blue over MCP and PIP joints on extensor sides of elbows and knees) over MCP joints, elbows and knees. (Dermatomyositis)
• Mechanic's fingers
  • Cracked fingertips (Antisynthetase syndrome)
• Arthritis (usually in fingers)
• * V-shaped eczema (neck / chest) (Dermatomyositis)
• * Shawl-shaped eczema (neck) (from the neck-shoulder blade) (Dermatomyositis)
• * Heliotropic rash (eyelids, most often children with dermatomyositis)
• Scleroderma (overlap of systemic sclerosis (Sklero myositis) or MCTD)
• Calcinosis (More often in children (Juvenile dermatomyositis)
• Raynaud's phenomenon (three-phasic, especially by antisyntetase syndrome)Lungs
• Cancer over lungs at auscultation

Heart

• Rhythm disturbances of the heart (myocarditis?)
• Heart failure (by myocarditis)

Blood tests

• Hgb, SR, CRP, leukocytes, platelets, liver enzymes, K, Na, Cl, Ca, Creatinine, TSH, f-T4, Creatine kinase (CK) troponin
• * Creative kinase (CK), LD and ASAT usually show high values
• Troponin T is often elevated
  • There may be a manifestation of the heart muscle
  • False elevated Troponin T values, however, are not rare.
    • Troponin T can be increased by
      • Myocardial Injury (heart attack, heart failure, cardiac contusion, cardiac amyloidosis, cardiac sarcoidosis
      • Acute aortic dissection
      • Acute respiratory distress syndrome (ARDS)
      • Hypotension and shock
      • Muscle trauma
      • Pulmonary embolism
      • Kidney failure
      • Overtraining
      • Subaracnoidal hemorrhage and stroke
      • Inflammatory diseases
      • (reference: Valfaie M, 2014)
  • Troponin I is more heart muscle specific
• Antibodies are described on a separate page, please see here (in Danish)
  • A selection:
    • ANA, SSA / Ro (Signs Sjögren's syndrome or SLE?)
    • Jo-1, PL12, PL7 (Antisynthetase Syndrome?)
    • PMScl: Overlap of Systemic Sclerosis (scleroderma myositis)?
    • RNP: MCTD?
    • MDA-5 (Myocytis with severe lung infection)
    • HMGCR (Statin-associated myositis)
    • CCP (ACPA) Myositis at Rheumatoid arthritis
  • Myositis-specific antibody (MSA, Immunological Laboratory OUS)

*EMG (Electro-myography)

• Myopathic changes at 90%
  • Increased activity and spontaneous fibrillation, abnormal myopathic amplitude, short polyphase motor potential, bizzare high frequency discharge
  • Separates from motor neuron disease, peripheral polymyopathy and myasthenia
  • Toxic, metabolic myopathy gives similar EMG as myositis

MRI (Magnetic Resonance Tomography) of the thigh muscles

• Thigh muscles show inflammatory signs with edema, usually symmetrical. By fat suppression (T2) is seen (spotting edema), most along fascia. By inclusion body myositis, the entire muscle is infiltrated
• Identifies area of ​​biopsy

X-ray Oesophagus (esophagus) with contrast agent

• Swallowing function is examined with X-ray oesophagus (dynamic with swallowing contrast) or manometry (Gastromedical department)
• Displays usually dysmotility
  • Oro-pharyngeal swelling muscle is affected, upper 1 / 3 part of esophagus
  • Risk of aspiration pneumonia

CT (Computer Resolution) / HRCT (High Resolution Computed Tomography) of lungs

• Shows changes in lung tissue with "milk glass" (active inflammation) or fibrosis, honeycombing especially at Antisynthetase syndrome and eventually MDA-5 related (amyopathic) myositis
• Basic infiltrates are typical
• X-ray examination of the lungs is often normal, although widespread findings are made by CT examination

Kapillaroscopy (nail bed)

• Often pathological by dermatomyositis (vasculopathy)
  • Bleeding, decreased capillary density, mega-capillaries, altered capillary architecture
• Please read more about capillary copy here (in Danish)

* Biopsy (tissue test)

• Targeted muscle biopsy where MRI shows inflammation (most often musculus quadriceps or Deltoid).
• Admission to bed post with one night after biopsy due to pain and bleeding risk
• Agreement with pathology for in which medium the biopsy should be stored

* Histology (Result of tissue test)

• Musculoskeletal Inflammation with mixed degeneration, regeneration and necrosis
• Polymyositis
  • Inflammation is most in the muscle fibers: Endomyseal inflammation (accumulation of CD8 + T lymphocytes where some are observed inside non-dying cells). No vasculopathy or immune complex deposition.
• Dermatomyositis
  • Perifascicular infiltrate or atrophy (capillary loss and ischemic injury). Reduced capillary density and membrane-attack-complex immune complex deposition are typical. Dermatomyositis resembles vasculitis with inflammatory processes mainly around peripheral vascular blood vessels (B lymphocytes and CD4 + T cells or plasmocytoid dendritic cells)
• MHC1 upregulation At both PM and DM

Lung function tests

• FEV1, FVC, DLCO (% of expected value)

Malignancy investigation by Dermatomyositis

• If age over 40 years (or clinical suspicion)
• Gynecological examination, CT abdominal examination, electrophoresis urine / serum, hemofec, colonoscopy, possibly other us if clinical suspicion
• Alternatively: PET / CT examination
• Please read more about cancer and rheumatic disease here (in Danish)

Diagnosis of elevated serum creatinine kinase (CK)

• Consider myositis and differential diagnoses
• If CK is below 1000
  • The test is repeated without any prior physical activity
  • Trauma, physical overload, cramps, infections, injections, metabolic myopathy are among alternative causes
• At very high CK (over 10.000) consider: Rhabdomyolysis
  • Troponin T (CTnT) is not specific to the heart muscle and often exceeds the skeletal muscle involvement. Troponin I (cTnI) is more myocardial specific.

Differential diagnoses of myositis, please read more here (in Danish)

• Short summary
  • Nervous system disorders / Myopathy /ALS/MS (Paresthesia, pares, fasciculations, MR cerbrum)?
  • Polymyalgia / Temporal arteritis?
  • Pain Syndrome /Fibromyalgia?
  • Parkinson's disease

Norwegian Directorate of Health (Supervisor for referrals)

Myositis, BINDEVEVSSYKDOMMER.no

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