Metabolic Disorders Presenting as Vacuolar Myopathy

Abstract

Thirteen cases of vacuolar myopathy (6 males, 7 females), with age range of 4 months to 22 years and diagnosed over a period from 1986 to 1999, could be categorized into acid maltase deficiency (AMD) (n=6), carnitine deficiency (CD) (n=5), and mitochondria-lipid-glycogen myopathy (MLGM) (n=2), cases of AMD presented as floppy infants with reparatory infection, while cases of carnitine deficiency presented with progressive motor weakness with normal initial milestones. Delayed motor milestones and proximal muscle weakness was the presenting complaints in MLGM. The diagnosis in all these cases was established based on the morphological findings on muscle biopsy, namely demonstration of PAS positive material within the vacuoles in AMD, ragged red fibers, vacuoles containing neutral fats and abnormal mitochondria in CD. MLGM was characterized by the presence of PAS positive material and neutral fat. The diagnosis was confirmed by identification of abnormal mitochondria under electron microscope. The storage product appears to affect not only the muscle metabolism but also the normal structure function relationship. The study highlights the importance of supplementing routine histopathology with muscle histochemistry and election microscopy to delineate the conditions, which look similar in routine histology.