This test will also establish the presence and degree of cardiac involvement. The characteristic finding is shortening of the PR interval. There may also be enlargement of the QRS complex. All affected patients will demonstrate a myopathic pattern. A skin biopsy will establish acid alpha-glucosidase activity in cultured fibroblasts.
Light microscopy reveals large glycogen-containing vacuoles in nearly all muscle fibers.
These vacuoles can be further characterized histochemically as secondary lysosomes. In general, type I and type II muscle fibers are affected equally. Electron microscopy is used to classify sub-types of the vacuoles in which glycogen accumulates. Histopathological examination of muscle is not necessary to establish diagnosis. There is currently no effective medical treatment for the underlying disorder.