Ik vond dit over PSSM, lijkt wel wat op wat jij beschrijft.
Polysaccharide Storage Myopathy
Polysaccharide storage myopathy (PSSM) is characterized by abnormal accumulations of glycogen and complex polysaccharide in skeletal muscle fibers. A metabolic defect responsible for marked glycogen accumulation appears to involve abnormal regulation of glycogen synthesis, although the precise etiology remains unknown. This condition has been identified in Quarter Horses and related breeds (Paints, Appaloosas), Warmbloods, and draft horses. Pedigree analysis supports a familial basis for PSSM in Quarter Horses.
Horses with PSSM often begin having episodes of ER at a young age, when longed or broken to ride. Rest for a few days prior to exercise is a common triggering factor. Horses with PSSM may have only one episode per year, or be affected at every exercise session. Episodes are characterized by a tucked-up abdomen, muscle fasciculations, a camped-out stance, sweating, gait asymmetry, hindlimb stiffness, and reluctance to move. Some horses paw or roll, resembling colic. Myoglobinuria and recumbency occasionally occur with severe episodes. Serum CK and AST are increased during an episode (usually >10,000 U/L) and, unlike other forms of ER, subclinical episodes characterized by persistently elevated CK are common.
Definitive diagnosis of PSSM is based on the presence of PAS-positive inclusions in fast-twitch muscle fibers on muscle biopsy. Surgical biopsy to remove a small block (1.5" x 1.5" x 2") of semimembranosus muscle is recommended. The sample should be shipped chilled on dry ice, by overnight courier to a specialized laboratory.
Prevention of further episodes involves altering the diet and training regimen. To prevent excessive glycogen storage, grain and sweet feed are eliminated from the diet; extra calories are provided in the form of fat (e.g. 1–5 lb/day of rice bran). Increased utilization of glycogen and enhanced oxidative capacity are promoted by gradually increasing daily exercise and providing as much turn-out as possible.