Late‐onset Becker‐type muscular dystrophy in a Border terrier dog

A 9‐year‐old Border terrier was presented to a referral hospital after a 1‐year history of progressive stiffness and exercise intolerance. Neurological examination was consistent with a neuromuscular disorder. Serum creatine kinase activity was mildly elevated. A myopathy was suspected based on MRI findings and electrophysiological examination. Muscle histopathology was consistent with a severe non‐inflammatory myopathy of a dystrophic type. Immunofluorescence and western blotting confirmed a dystrophinopathy with an 80‐kDa truncated dystrophin fragment similar to Becker muscular dystrophy in people. To our knowledge, this is the first description of a late‐onset Becker‐type muscular dystrophy in a dog, and the first description of a dystrophinopathy in a Border terrier. Muscular dystrophy in dogs should not be ruled out based on late onset clinical signs and only mildly elevated creatine kinase.