Muscle Wasting Diseases

The Neuromuscular System

• The neuromuscular system, or peripheral nervous system, is part of the central nervous system. The neuromuscular system is composed of the nerves that leave the back of the brain to control the muscles and glands of the head (cranial) and peripheral nerves leaving the spinal cord to control the muscles of the limbs. The neuromuscular junction is where the nerves and muscles meet.

  The brain sends a signal to the nerves telling the muscle to perform certain motor activities such as standing, walking, running, chewing and swallowing. Every muscle in the body is controlled by its own peripheral nerve. As the signal is sent from the brain it crosses the neuromuscular junction with the help of a chemical called acetylcholine. As the signal reaches the muscle, this causes the muscle to react. Diseases of the neuromuscular system will affect the nerves leading to the muscles (neuropathy), the neuromuscular junction or the muscle fibers (myopathy).

Symptoms

• Symptoms of neuromuscular disorders may include muscle weakness, muscle atrophy, gait abnormalities, skeletal deformities, muscle hypertrophy (increase in muscle mass), dysphagia (difficulty swallowing), difficulty breathing and paralysis.

Diagnosis

• Diagnosing muscle diseases is difficult because of the many different types that present with common symptoms. Other diseases must be ruled out before a diagnosis of a neuromuscular disease is made. Some diseases are more common to specific breeds of dogs, so this will give your veterinarian a good starting point. A complete history and clinical exam will be performed as well as a complete blood count and blood chemistry panel. X-rays of the chest and abdomen and an abdominal ultrasound may also be performed. If a diagnosis is still unclear, a muscle biopsy may be obtained and your veterinarian may perform an electromyography, which measures electrical activity in the muscle.

Treatment/Prognosis

• Treatment and prognosis of neuromuscular diseases largely depends on the type of the disease. Treatment may include drug therapy, surgery, physical therapy and muscle support. Prognosis for some neuromuscular diseases is very poor, these include hereditary neuropathies and hereditary myopathies as well as those caused by cancer. Other diseases have a good prognosis with correct treatment and support. These include myositis, myasthenia gravis, distal denervating disease and most forms of polyradiculoneuritis. It is important to note that treatment may be prolonged and it can take several weeks before conditions begin to improve.

Myopathy

• A myopathy is a disease that affects the function of the muscle fiber resulting in muscular weakness. Myopathies can be congenital, inflammatory, metabolic, nutritional, chemical, idiopathic (no known cause) or traumatic. Some common myopathies seen in veterinary practice include myositis associated with toxoplasmosis and neosporosis, masticatory myositis, polymyositis, atrophic myopathy, steroid/Cushing's myopathy and Labrador retriever hereditary myopathy.

Neuropathy

• Neuropathies are diseases that cause abnormal functions of the motor and sensory nerves. Neuropathies are categorized based on the type of nerve affected and the area of the body affected. There are many different types of neuropathies. They can be congenital, inflammatory, traumatic, metabolic, idiopathic and vascular. Some of the more common neuropathies seen in veterinary practice include hypothyroid neuropathy, idiopathic polyradiculoneuritis, traumatic neuropathies, toxoplasma/neospora polyradiculoneuritis, chronic relapsing inflammatory demyelinating polyneuropathy and idiopathic facial paralysis.