Neuromuscular Disorders

What are neuromuscular disorders?

Neuromuscular disorders represent a broad range of conditions that involve dysfunction of peripheral nerves, muscles or the communication between them. This most often results in muscle weakness, muscle atrophy (loss) and disturbance of sensation (like numbness and tingling). Neuromuscular disorders can cause other symptoms as well, depending on the type.

What are the different types of neuromuscular disorders?

There are several subgroups of neuromuscular disorders based on the area of dysfunction, with several types of conditions in each subgroup.

A neuromuscular disorder represents any condition that affects the structure and/or function of any component of your neuromuscular system, including:

• Anterior horn cells.
• Nerve roots (including dorsal root ganglia).
• Plexuses (like the brachial plexus and lumbosacral plexus).
• Peripheral nerves.
• Neuromuscular junction.
• Muscle fibers.

Anterior horn cell conditions

Anterior horn cell diseases are often progressive, degenerative diseases (they get worse with time) of the motor neurons. Motor neurons are the cells in your brain and spinal cord that allow you to perform all movements, like walking, speaking and breathing. They relay commands from your brain to the muscles that carry out these functions.

Anterior horn cells specifically are motor neurons that are in the grey matter of your spinal cord. They’re essential for the movement of your skeletal muscles. The breakdown of these cells causes a lack of nerve supply (denervation) to your muscles, resulting in weakness.

Anterior horn cell diseases include:

• Amyotrophic lateral sclerosis (ALS, or Lou Gehrig’s disease).
• Spinal muscular atrophy.
• Spinal-bulbar muscular atrophy (SBMA), or Kennedy’s disease.
• Polio.

Plexus disorders (plexopathies)

Soon after emerging from your spine at different spinal levels, the nerves may intermingle to form a complex network, or plexus. There’s a plexus in your upper limbs called the brachial plexus. And there’s another in your lower limbs called the lumbar or lumbosacral plexus.

These plexuses may be vulnerable to various types of injuries, like those from trauma, compression or even inflammation. This may cause pain, numbness and tingling, and weakness in the affected limb.

Nerve root conditions

Nerve roots are the short branches of a spinal nerve. Spinal nerves exit your spinal cord along the length of your spine between your vertebrae (spine bone segments). Each spinal nerve contains motor nerve root and sensory nerve root fibers. Motor nerve roots contain nerve fibers that carry commands from your brain and spinal cord through your peripheral nerves to your muscles.

When surrounding tissues press on nerve roots, it can cause pain, numbness and tingling in different areas of your body. This is called radiculopathy. Compression of motor nerve roots causes muscle weakness.

There are different types of radiculopathies based on where the pinched nerve is along your spine:

• Neck (cervical radiculopathy).
• Middle to upper back (thoracic radiculopathy).
• Low back (lumbar or lumbosacral radiculopathy).

Peripheral nerve conditions

“Peripheral neuropathy” is an umbrella term for nerve diseases that affect any of the nerves outside of your brain and spinal cord (peripheral nerves). There are several types and several causes. You can’t move your muscles without the proper functioning of peripheral nerves, which is why these conditions fall under the even broader category of neuromuscular disorders.

Peripheral neuropathies may affect only parts of your body or most of your body. The most common form of peripheral neuropathy affects the parts of your limbs farthest away from your core, especially your feet and hands.

Examples of peripheral neuropathies include those related to:

• Diabetes.
• Alcohol use disorder.
• Malnutrition.
• Amyloidosis.
• Genetic or inherited causes like Charcot-Marie-Tooth disease.
• Autoimmune or inflammatory causes like chronic inflammatory demyelinating polyneuropathy (CIDP) and Guillain-Barré syndrome.
• Toxic exposures due to toxic chemicals, like cleaning fluids or pest killers.

Neuromuscular junction conditions

The neuromuscular junction (NMJ) is a connection (synapse) between the end of a motor nerve and a muscle. To communicate with the muscle, motor nerves release a molecule across the synapse called acetylcholine. Issues with this communication lead to certain neuromuscular junction disorders.

The main conditions that affect the NMJ include:

• Botulism.
• Lambert-Eaton myasthenic syndrome (LEMS).
• Myasthenia gravis.

Muscle conditions

Myopathies are conditions that directly affect your skeletal muscles (muscles that connect to your bones). These diseases attack muscle fibers, making your muscles weak. There are several types of myopathies. Some you’re born with (they’re genetic or inherited) and some you can develop later in life.

Myopathies don’t include direct muscle injuries, like a muscle tear, strain or bruise.

Muscular dystrophy

Muscular dystrophy refers to a group of more than 30 genetic (inherited) conditions that affect the functioning of your muscles. Some forms include:

• Duchenne muscular dystrophy (DMD). This is the most common type.
• Becker muscular dystrophy (BMD).
• Myotonic dystrophy.
• Oculopharyngeal muscular dystrophy (OPMD).

Autoimmune and inflammatory myopathies

Autoimmune and inflammatory myopathies are conditions that happen due to issues with your immune system that cause problems with muscle function. Examples include:

• Dermatomyositis.
• Polymyositis.
• Immune-mediated necrotizing myopathy.

Other myopathies

Other myopathies include those related to:

• Electrolyte imbalances: Electrolyte imbalances, like hypercalcemia (high blood calcium) and hyperkalemia (high blood potassium), can cause muscle issues.
• Endocrine myopathies: These happen when hormones interfere with muscle function. This can happen from issues with your thyroid, parathyroid glands or adrenal glands, for example.
• Metabolic myopathies: Issues with genes that give instructions for enzymes that your muscles need cause metabolic myopathies. Examples include glycogen storage diseases and lipid storage disorders.
• Mitochondrial myopathies: These happen when there’s a defect in muscle mitochondria, which are the energy-producing part of cells.
• Periodic paralysis: Periodic paralysis is a group of inherited neurological disorders. They involve episodes in which your muscles become slack, weak and unable to contract.
• Toxic myopathies: This happens when a toxin or medication interferes with muscle structure or function.

What are the most common neuromuscular disorders?

Peripheral neuropathy is the most common type of neuromuscular disorder. This is mainly because it has several types and causes. Researchers estimate that more than 20 million people in the U.S. have some form of peripheral neuropathy.

But most people don’t think of peripheral neuropathies as neuromuscular disorders, as they have their own group. Some of the most well-known — but ultimately rare — neuromuscular diseases include ALS and muscular dystrophy.

About 30,000 people in the U.S. have ALS, with an estimated 5,000 new cases diagnosed each year. All the different types of muscular dystrophy combined affect about 16 to 25 per 100,000 people in the U.S.

What are the symptoms of neuromuscular disorders?

Symptoms of neuromuscular disorders vary based on the specific type. But in general, muscle-related symptoms may include:

• Muscle weakness.
• Muscle atrophy (loss).
• Muscle twitches (fasciculations), cramps or spasms.
• Muscle pain.
• Spasticity.
• Difficulty walking.
• Issues with coordination and balance.
• Drooping eyelids or other facial features.
• Difficulty speaking due to tongue weakness or weakness of other oral or facial muscles (dysarthria).
• Difficulty swallowing (dysphagia) due to throat (pharynx) muscle weakness.
• Difficulty breathing due to diaphragm muscle weakness.

Other symptoms may include:

• Fatigue.
• Numbness.
• Tingling or other abnormal sensations (paresthesia).

What causes neuromuscular disorders?

Neuromuscular disorders have many different causes. But a some of them are genetic. This means that you inherited the genes from your biological parents, or a genetic mutation (change) happened randomly. A neuromuscular disorder may result from an error in a single gene or several genes.

Some neuromuscular disorders are autoimmune diseases. Others are a result of an injury, nutritional or metabolic disturbance, toxin exposure or inflammation. Sometimes, there’s no known cause.

How are neuromuscular disorders diagnosed?

Your healthcare provider will ask about your medical and family history, medications and symptoms. They’ll do a general physical exam and then a neurological exam. This is a specific type of physical exam that helps identify signs of disorders affecting your brain, spinal cord and peripheral nervous system (including muscles).

Your provider may refer you to a neurologist for further evaluation. Other tests that help diagnose neuromuscular disorders include:

• Electromyography (EMG): This test evaluates the health and function of your skeletal muscles and the nerves that control them.
• Nerve conduction test: This test evaluates the function of your peripheral nerves.
• Blood tests: These tests can check for a variety of things, like enzyme abnormalities and markers of autoimmune conditions.
• Imaging tests: Tests like an MRI, CT scan and neuromuscular ultrasound can “see” any issues with your brain, spinal cord and/or nerves.
• Muscle biopsy: This procedure involves taking a small sample of your muscle tissue so a pathologist can check it under a microscope for abnormalities.
• Genetic testing: This testing can confirm certain genetic neuromuscular disorders.

What is the treatment for neuromuscular disorders?

Treatment for neuromuscular disorders varies widely depending on the specific type. In general, many neuromuscular disorders don’t have a cure. But there may be treatments and therapies that can improve the symptoms and stop or slow the condition’s progression. Your treatment may consist of:

• Medications.
• Physical and occupational therapy.
• Speech therapy.
• Nutrition therapy.
• Assistive devices to help with mobility.
• Procedures, including surgeries.

A neurologist (including a neuromuscular specialist) will likely be your go-to healthcare provider for a neuromuscular disorder. But depending on the type, you may need additional providers. They could include:

• Physical and occupational therapists.
• Rheumatologists.
• Pulmonologists and respiratory therapists.
• Pathologists.
• Surgeons.
• Orthopaedists.
• Speech-language pathologists.
• Dietitians.
• Psychologists.
• Social workers.

What can I expect if I have a neuromuscular disorder?

Many neuromuscular disorders are chronic (lifelong). While many don’t have cures, medication and other therapies can help manage symptoms, as well as stop or slow down their progression. Your healthcare provider will be able to give you a better idea of what to expect based on your specific condition.