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Polysaccharide Storage Myopathy in Cob Normand Draft Horses

INRA, UMR703, Ecole Nationale Veterinaire, Nantes, F-44307 France (TL, LG, YC), INRA, Laboratoire de Genetique biochimique et de Cytogenetique, Jouy-en-Josas, F-78350 France (BH, SC, GG), and MSD-Chibret, Centre de recherche Mirabel, Riom, Clermont-Ferrand, F-63963 France (SMN)

Abstract

Gluteus medius muscle was sampled from 53 Cob Normand horses for histologic evaluation. Twenty horses (38%) exhibited amylase-resistant material in myocytes consistent with polysaccharide storage myopathy. Diameter of affected type II fibers was increased (67.7 ± 21.4 µm) compared with normal ones (57.3 ± 19.7 µm). Two groups were distinguished by quantitative study. The first group (n = 14; 26%) was characterized by a low percentage of fibers (m = 0.98%) containing aggregates occurring singly or in perifascicular clusters without myopathic changes. The second group (n = 6; 11%) was characterized by a high percentage (m = 18.1%) of fibers containing aggregates scattered in biopsy with chronic myopathic changes. Rebiopsy of 4 horses showed an increase with time in the number of aggregate-containing fibers for horses of the first group only. In 1 necropsied horse, aggregates were observed in a wide range of muscles including smooth muscles. Ultrastructurally, granular material was found interspersed among arrays of filamentous material.

Key words: Histopathology; horses; myopathy; polysaccharide storage.