Inclusion Body Myositis

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