Myopathy: A Closer Look

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Transcript of Myopathy: A Closer Look

  1. 1. Myopathy: A Closer Look Sofiya Prilik, MD Physical Medicine and Rehabilitation
  2. 2. Myopathy
    • Definition
    • neuromuscular disorders in which the primary symptom is muscle weakness due to dysfunction of muscle fiber.*
    • * Definition by the National Institute of Neurological Disorders and Stroke
  3. 3. Let Start With Basics!
  4. 4. Muscle Anatomy: gross and microscopic
  5. 6. MUSCLE FIBER
  6. 7. Function of Muscle
  7. 9. Motor Unit A motor unit is made up of a motor neuron and all the muscle cells it stimulates. Motor units vary in size. Small motor units are used for precise, small movements; large motor units are are used for gross movements.The number of cells within a motor unit determines the degree of movement when the motor unit is stimulated. Muscle tone is maintained by asynchronous stimulation of random motor units.
  8. 11. Normal Muscle
  9. 12. Characteristics of the Three Muscle Fiber Types Fiber Type Slow Twitch Type I Fast Twitch A Type IIA Fast Twitch B Type IIB Contraction time Slow Fast Very fast Size of motor neuron Small Large Very large Resistance to fatigue High Intermediate Low Activity used for Aerobic Long term anaerobic Short term anaerobic Force production Low High Very high Mitochondrial density High High Low Capillary density High Intermediate Low Oxidative capacity High High Low Glycolytic capacity Low High High
  10. 13. Abnormal Muscle
  11. 14. Myopathy: symptoms
    • Muscle Weakness
      • Proximal Muscles>distal muscles
      • Fatigue
      • Difficulty rising from a chair, floor, tub
      • Difficulty with stairs
      • Difficulty with overhead tasks
      • Respiratory muscles
      • Bulbar weakness- speech, swallowing, oculomotor, facial
  12. 15. Myopathy: symptoms
    • Pain
      • Mostly with inflammatory and metabolic
      • High serum CK level
      • Aching, dull, cramping
      • Patients will say: sore, ache, spasm
      • No numbness or paresthesias
  13. 16. Physical Exam:
    • Full exam is important !
    • Observation look for muscle atrophy, deformities
    • Strength testing manual muscle test
    • ROM testing
    • Functional testing
      • Stand up from a chair
      • Walk
      • Step up on a low stool
    • Dont forgetREFLEXESandSENSATION
  14. 17. Myopathic Disorders
    • Inflammatory Myopathies
      • Polymyositis
      • Dermatomyositis
      • Inclusion body myositis
      • Viral
    • Muscular dystrophies
      • X-linked
      • Limb-girdle(ar/d)
      • Congenital
      • Fasioscapulohumeral (ad)
      • Scapuloperoneal (ad)
      • Distal (Welander) (ad/r)
    • Myotonic Syndromes
      • Myotonic dystrophy (ad)
      • Inherited
      • Schwarz-Jampel
      • Drug-induced
    • Congenital myopathies
      • Central core disease
      • Nemaline myopathy
      • Myotubular
      • Fiber-type disproportion
    • Metabolic myopathies
      • Glycogenoses
      • Mitochondrial
      • Periodic paralysis
    • Endocrine myopathies
      • Thyroid
      • Parathyroid
      • Adrenal/steroid
      • Pituitary
    • Drug-induced/toxic
  15. 18. Myopathy: types
    • Muscular dystrophies
      • Inherited
      • Abnormal muscle proteins
      • Progressive course and early onset
    • Congenital
      • Slowly progressive or non-progressive
      • Distinct finding on muscle biopsy
  16. 19.
    • Metabolic
      • Defect in intracellular energy production
    • Inflammatory
      • Acquired
      • Caused by immune or infectious process
      • Almost always are associated with elevated Creatinine Kinase level in serum.
    • Atrophic
      • Drug-induced (Colchicine, AZT, ETOH, Statins (1/10,000 per year)
      • Endocrine (steroid)
      • CK is most often normal
  17. 20.
    • Myotonic
      • Congenital or adult
      • Cardiopulmonary compromise
  18. 21. Epidemiology
    • Worldwide incidence of all inheritable myopathies is about 14%
    • Overall incidence of muscular dystrophy is about 63 per 1 million.
    • Worldwide incidence of inflammatory myopathies is about 510 per 100,000 people. More common in women
    • Corticosteroid myopathy is the most common endocrine myopathy and endocrine disorders are more common in women
    • Overall incidence of metabolic myopathies is unknown.
  19. 22. Diagnosis
    • Case:
      • 59 year-old male with history of smoking, who was diagnosed with severe COPD/emphysema 2.5 years ago.Since then, he had several hospitalizations due to worsening SOB and productive cough.He was treated with high doses of IV corticosteroids followed by very slow oral steroid tapers.After the last hospitalzation 4 months ago,he has been maintained on a Prednisone 5 mg daily.
      • Normally, the patient is independent with transfers, ambulation and ADLs.His walking tolerance is about 1-2 blocks, limited by SOB.
      • 2 weeks ago, patient presented to his PMD c/o progressive functional decline in walking tolerance, and especial difficulty with transfers and stairs.
      • Exam revealed a thin male, with O2 saturation of 93% on RA. No apparent respiratory distress was noted. No cushinoid features were seen. Pertinent positives included visibly apparent atrophy in the proximal muscles groups of both UE and LE.Strength testing was within normal limits.Patient had difficulty standing up from a sitting position.He was unable to perform squats.
      • Labs WBC 11.8, Glu 120, otherwise normal.CK - normal
      • NCS/EMG - normal
  20. 23. DIAGNOSIS
    • Steroid induced myopathy.
  21. 24. STEROID INDUCED MYOPATHY
    • Insidious disease process
      • weakness ofproximal muscles of the upper and lower limbsandneck flexors.
      • First described by Cushing in 1932
      • An excess of either endogenous or exogenous corticosteroids is believed to cause the condition.
      • Chronic or acute (less common)
      • Catabolic effect on muscle gluconeogenesis from aminoacids
  22. 25. STEROID INDUCED MYOPATHY
    • Fluorinated steroids are implicated
      • Dexamethasone
      • Triamcinolone
    • Also seen with non-fluorinated ones
      • Prednisone
    • Inhaled steroids
  23. 26. Pathophysiology
    • decreased protein synthesis
    • increased protein degradation
    • alterations in carbohydrate metabolism
    • mitochondrial alterations
    • electrolyte disturbances
    • decreased sarcolemmal excitability
  24. 27. Epidimiology
    • For a given dose of steroid, women appear to be twice as likely as men to develop muscle weakness
    • Worldwide incidence or prevalance is unknown
  25. 28. Diagnostic studies
    • Labs
      • Routine Labs
      • Special labs
        • Creatinine Kinase normal
        • Urine Creatinine increased
        • No myoglobinuria or rhabdomyalysis
      • Muscle biopsy
        • type IIB fibers are mostly affected
        • No inflammation, necrosis or regeneration
  26. 29. DIAGNOSTIC STUDIES
    • Electrodiagnostic studies
      • Normal nerve conduction studies (NCS)
      • Electromyography can be normal
        • (EMG tests type I