There are 2 previously reported inherited myopathies affecting Labrador retrievers: CNM also known as centronuclear myopathy and CXMD known as canine X-linked muscular dystrophy.
Labrador retriever myopathy also known as Centronuclear myelopathy is an inherited (autosomal recessive) muscle condition that causes changes in the gait of young Labrador Retrievers. Recently the causative genetic mutation has been identified and a DNA test made commercially available.
Affected dogs have predominance of Type I muscle fibres and deficiency of Type II muscle fibres. Type I muscle fibres are referred to as slow-twitch fibres and they are used when minimal muscular activity is required. Type II muscle fibres are known as fast-twitch fibres and they are used when a lack of oxygen develops during maximal stimulation (e.g. during prolonged or endurance exercise).
Dogs with CXMD typically show clinical signs at birth or very early in life consisting of stiff pelvic limbs, weakness, bunny hopping gait, excessive salivation, tongue enlargement, and difficulty swallowing.
Dogs with CNM typically present with clinical signs at less than 5 months of age and include skeletal muscle loss, stunted growth, wobbliness, and weakness. Signs are progressive until the animal reaches maturity (between 6 and 12 months), when they stabilize. Animals may have a normal life span. Severely affected dogs exhibit a low head carriage and a short stride, stilted gait. Clinical signs are worse with stress, exercise, excitement, or cold temperatures.
A definite diagnosis usually requires a urine test, muscle biopsy, and electromyography. Results of blood tests show that the creatinine phosphokinase (enzyme for storing energy in muscles) levels are normal which indicates that there is no damage to the muscle tissue.
Muscle biopsies taken from large muscle groups of affected dogs show a variation in muscle fiber diameter and a deficiency of Type II muscle fibers. Results of neurological examination and nerve function tests are often normal.
Rehab focuses on addressing muscle loss, wobbliness and weakness through targeted exercises. We focus on improving proprioception. Proprioception is the ability to sense where our limbs are in space. Our techniques are pulled from what they do in humans and at Walking Paws Rehab we translate them to animals. Once proprioception is improved we work on stability. We start with positional balance exercises and then progress into dynamic movements. We then focus on increasing strength of the hind limbs and core muscles. We focus on retraining transitions and taking appropriate steps. Fine tuning those movements is very important for a dog’s day to day routine.
