Non-Inflammatory Muscle Disease in Cats

A kitten is born with this muscle weakening condition, but may not show signs of a problem until up to a year old. The feline will appear to experience overall weakness, she may stand in a hunched posture, and the tongue may protrude from the mouth. Over time, the condition will worsen, eventually affecting the heart and lungs.

Non-inflammatory muscle disease in cats, or non-inflammatory myopathy, is a progressive disease of muscle degeneration caused by a deficiency of a muscle-membrane protein. When a veterinarian talks about muscle myopathies (muscle diseases), he or she is referring to a disease affecting the muscles that are not linked to any neuromuscular junction or disorder of innervation. 

The hallmark of non-inflammatory muscle disease in cats is severe hypertrophy of the proximal and axial appendicular skeletal muscles. In some felines, the diaphragm and tongue also display massive hypertrophy. Over time, a feline may develop potentially life-threatening complications due to the impaired skeletal muscles, such as heart disease. The telltale signs that your cat could be suffering from non-inflammatory muscle disease are listed below: 

Clinical signs of muscle weakness

• Ventroflexion of the neck (head is positioned downward) 
• General weakness 
• Exercise intolerance 
• Collapse 
• Paralysis 

General Symptoms

• Hunched posture 
• Limited joint mobility 
• Pain 
• Plantigrade stance 
• Muscle degeneration (muscle mass depletion) 
• Stiff gait 
• Regurgitation 
• Dysphagia (difficulty swallowing) 

Non-inflammatory muscle disease in cats is commonly inherited from parent to offspring, caused by a deficiency of a protein found on the X-chromosome;  a dystrophin deficiency. Dystrophin is a large protein indirectly connected to the internal cytoskeletal system. When a cat’s genes are mutated, the X-chromosome is affected and the x-linked piece of DNA becomes a recessive inheritance to offspring. Although cats are born with the protein mutation, clinical signs do not become present until about 10 weeks of age. Devon Rex and Domestic Shorthaired cats are commonly affected by this disease, although no true breed connection has been made. 

Diagnosing a cat with non-inflammatory muscle disease is a long process, as the veterinarian will want to rule out a number of commonly occurring diseases beforehand. Common feline diseases that mimic non-inflammatory muscle disease include arthritis, neoplasia, nerve degeneration, metabolic or systemic disease.  The diagnostic process with begin with a physical exam, as the veterinarian will play with the positioning of the cat’s limbs and evaluate her skeletal muscles. A medical history review will take place and the feline doctor will ask you a series of questions, relevant to the patient case. 

Be prepared to answer the following questions during your visit with the veterinarian: 

• What are the exact symptoms you have noted at home of concern? Could you describe them?
• How long have these symptoms persisted? 
• What is considered “normal” activity and behavior for your cat?
• Has your cat had any difficulty eating or does she/he regurgitate her food?
• Has your cat suffered from any recent trauma? (Hit-by-car, falls, etc.)

Answering the questions your veterinarian provides, paired with a physical examination, will aid in the doctor’s diagnostic plan. Based on what the vet believes could be the possible problem, he or she will proceed to conduct the following diagnostic tests: 

• CBC or complete blood cell count 
• Biochemistry profile (blood test to evaluate organ function) 
• Urinalysis 
• A CT scan
• MRI 
• Radiograph of the brain
• Muscle biopsy 
• DNA test (to determine genetic nature of the disease) 

Non-inflammatory muscle disease has no cure and is irreversible. The only option for cat owners is to manage their cat’s non-inflammatory muscle disease with therapeutic drugs. Pain management and the use of glucocorticosteroids are the norm for medical treatments for this feline disease, but usually have minimal effects. Therapeutic practices at home, such as hydrotherapy or swimming, may be recommended to encourage easy muscle movements. 

At home, the best way to aid in your cat’s non-inflammatory muscle disease is to provide a comfortable, stress-free environment. A soft bed and low-impact physical activities can keep your cat comfortable in her condition. Physical activity is encouraged, but the time spent playing or time of play may be limited as cardiac arrest is possible.

Unfortunately, the overall prognosis for non-inflammatory muscle disease in cats is very poor. Feline muscle disease is irreversible and eventually leads to life-threatening conditions such as cardiac disease, or aspirate pneumonia. Your veterinarian will discourage the feline from all breeding programs in order to discourage passing the muscle abnormality to offspring. However, despite your cat’s disease, a fulfilling life is possible until the condition reaches potentially fatal limits. Ask your cat’s doctor about the best management options for non-inflammatory muscle disease in cats as many options are available before euthanasia should be considered.