What is Hereditary Muscle Disease (Non-inflammatory Myopathy in Labrador Retrievers)?
Labrador Retrievers can inherit a muscle disease called Centronuclear Myopathy (CNM). This is a non-inflammatory disease that causes weakness and deficiency in type II muscle fibers. On a cellular level, it is characterized by an excessive number of internalized nuclei in the muscle cells. First discovered in 1976, CNM has since been studied enough to identify that it is inherited as an autosomal recessive trait in Labrador Retrievers, especially black and yellow labs. A similar disease has also been found in Great Danes and Bouviers Des Flandres. Animals carrying the mutation will typically start to show symptoms between 8-12 weeks of age, but occasionally onset can be delayed as late as six months. The most notable sign is an abnormal gait or a “bunny-hopping” tendency in the back legs. Dogs also have generalized muscle weakness that often becomes more remarked with cold temperatures or excitement. The disease gets progressively worse over the first year of the dog’s life, but after about twelve months of age symptoms will taper off and some animals may even see improvement. There is no cure, but many Labradors with mild CNM can live a normal life although they may be somewhat weaker and have a reduced ability to exercise. Very severe symptoms can be difficult to manage and rarely dogs may develop megaesophagus, weakness and overstretching of the esophageal muscles, as a complication.
Inherited muscle disease can cause weakness and abnormal gait in Labrador Retrievers. This is called centronuclear myopathy. It usually becomes apparent in the first year of a dog’s life.
Book First Walk Free!
Symptoms of Hereditary Muscle Disease (Non-inflammatory Myopathy in Labrador Retrievers) in Dogs
These are some of the sign you might see in a Labrador puppy with CNM.
- Abnormal (bunny-hopping) gait
- Arched back
- Abnormal stance
- Flexion of the neck and cervical spine (ventroflexion)
- Stunted growth
- Atrophied or shrunken muscles
- Generalized muscle weakness (worse with cold, exercise, or excitement)
- Decreased exercise tolerance
- Difficulty swallowing and aspiration pneumonia (megaesophagus)
There is only one type of CNM. Other inherited conditions in Labrador Retrievers that could produce similar symptoms include Exercise Induced Collapse (EIC), which is related to a neurological condition and usually takes the form of an attack during strenuous exercise, and X-linked myotubular myopathy which is found only in males and has more severe symptoms.
Causes of Hereditary Muscle Disease (Non-inflammatory Myopathy in Labrador Retrievers) in Dogs
CNM is inherited as an autosomal recessive trait, so affected animals will carry the gene from both parents. Dogs inheriting the disease from only one parent will be asymptomatic, but they can still pass CNM on to their offspring.
Diagnosis of Hereditary Muscle Disease (Non-inflammatory Myopathy in Labrador Retrievers) in Dogs
CMN is diagnosed symptomatically and through ruling out other diseases that could cause similar symptoms. The veterinarian will physically examine your dog and take blood and urine tests to evaluate for infection. Creatine kinase may be slightly elevated on a blood test. Since this is a hereditary condition, your dog’s breed, age, and family history will all be important.
Definitive diagnosis is made with electromyography and muscle biopsies. Electromyography will examine muscle strength during stimulation, especially in the front limbs and jaw muscles. Dogs with only mild symptoms may show little or no abnormality with electromyography. Microscopic examination of a sample obtained through a muscle biopsy will reveal weakness and atrophy in the fibers and as well, an increase in the cells’ central nuclei. A muscle biopsy is an invasive procedure that involves inserting a hollow needle in the muscle to obtain a tissue sample. DNA testing can also reveal whether Labrador Retrievers carry the mutation that causes CMN. This can be an important diagnostic test before an animal is bred, especially if one or more sibling has CMN.
Treatment of Hereditary Muscle Disease (Non-inflammatory Myopathy in Labrador Retrievers) in Dogs
There is no effective treatment for CMN. Keeping warm temperatures in your house can help to reduce the severity of symptoms. L-carnitine supplements have also been found to increase muscle strength in some dogs and may be recommended to help manage the condition. Clinical signs may also be reduced with diazepam, however, this medication will have side effects with long-term use. Some dogs show a marked improvement as they reach adulthood, so treatment may only be necessary in the first year of life.
Recovery of Hereditary Muscle Disease (Non-inflammatory Myopathy in Labrador Retrievers) in Dogs
Mild cases of CMN are usually manageable by reducing exercise and eliminating cold temperatures. Many dogs with CMN still make good pets although some lifestyle changes may be necessary. Very severe symptoms could limit your dog’s life, especially if megaesophagus develops as a complication. This can sometimes be managed with diet change and improved feeding posture, but aspiration related pneumonia becomes an increased risk. Very severely affected dogs could need to be euthanized, but this is rare with CMN.
Hereditary Muscle Disease (Non-inflammatory Myopathy in Labrador Retrievers) Questions and Advice from Veterinary Professionals
I have an 11 year old lab with CNM. He has lived a wonderful life, with some frustrating times. He is full of life & love to this day. In the last year & a half he is no longer able to stand up With out assistance. Once he is standing he is able to walk outside & even go on very short walks. My question is, do you think he is in any pain? Would a medication like Rimadyll help him at all at this point. He doesn't seem in any discomfort, but I am concerned. I really don't know where to get advice, as it seems to be quite uncommon where I live. Most vets try to treat him as a normal dog. Thanks in advance.
Jasper may be in pain; whilst the condition itself isn’t painful, any anomalies that occur due to the condition may cause pain. Dogs are stoic by nature and hide pain from their owners (they don’t want to look weak), this can make it difficult to determine whether there is pain or not. I cannot comment as I haven’t examined Jasper, but a conversation with your Veterinarian about pain and look for pain during flexion and palpation etc... may help ease your concerns. Regards Dr Callum Turner DVM
Thank you for your advice. Do you know if there are any vets in Minnesota that know anything about CNM?
Add a comment to Jasper 's experience
Was this experience helpful?
My dog a chocolate lab is exhibiting signs of this, CMN. He was born on 7-22-16 and last Friday 1-13-17 he began to limp and walk funny, by Monday 1-16-17 he was incapable of walking more than 10 feet and today he cant pick himself up. He has been at the vet, we have him home with us now. They have sent the blood test off and we are awaiting the results. He has had poor posture and not sit like a normal lab, since we have had him. His sires papers say he is clear of CNM, not sure on the moms side. I'm just wondering if this would come on this quick? This weekend is was cold and wet? He has completely changed for this worse in 5 days, his attitude is still great, very loving and seems happy, he just tires very quickly.
Centronuclear myopathy (CNM) is a recessive hereditary myopathy of Labrador Retrievers where two carriers (I would question the sires papers if it is CNM) of the affected genes are mated resulting in (statistically) one clear pup (no mutation), two carrier pups (carrying one mutated gene) and one affected pup (carrying two mutated genes). The progression of the condition is exasperated by cold weather but is usually progressive over a few months. The Veterinary Genetics Laboratory at UCDAVISVeterinarySchool offer a genetic test (simple at home cheek swab) from $50 (contact them for specific pricing). Regards Dr Callum Turner DVM
Add a comment to Patten's experience
Was this experience helpful?