Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content + Download Section PDF Listen ++ For further information, see CMDT Part 24-35: Myopathic Disorders + Key Features Download Section PDF Listen +++ ++ Unknown cause Begins insidiously, usually after middle age + Clinical Findings Download Section PDF Listen +++ ++ 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 Download Section PDF Listen +++ ++ 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 Download Section PDF Listen +++ ++ Corticosteroid and immunosuppressive therapy is sometimes offered but usually ineffective Intravenous immunoglobulin (IVIG) therapy is not recommended