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Key Features

  • Unknown cause

  • Begins insidiously, usually after middle age

Clinical Findings

  • Progressive proximal weakness of first the lower and then the upper extremities, and affecting facial and pharyngeal muscles

  • Weakness often begins in the quadriceps femoris in the lower limbs and the forearm flexors in the upper limbs

  • Distal weakness is usually mild

Diagnosis

  • Serum creatine kinase levels may be normal or increased

  • Muscle biopsy confirms diagnosis

  • Anticytosolic 5′-nucleotidase 1A antibodies

    • Detected in one-third of cases

    • May be associated with a more severe phenotype

Treatment

  • Corticosteroid and immunosuppressive therapy is sometimes offered but usually ineffective

  • Intravenous immunoglobulin (IVIG) therapy is not recommended

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