Neuromuscular Disorders: Types, Symptoms & Treatment

 

Neuromuscular disorders can all affect peripheral nerves, muscles, or the communication between them. Neuromuscular disorders come in hundreds of different types. Muscle weakness is the most prevalent symptom among them all.

The nerves that transmit sensory information to the brain and regulate voluntary muscles are impacted by neuromuscular disorders. To help regulate voluntary muscles, nerve cells, or neurons, transmit and receive electrical signals. Communication between the nervous system and muscles is disrupted when neurons die or become unhealthy. Muscles weaken and atrophy as a result.

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What are Neuromuscular disorders?

A wide range of conditions are referred to as neuromuscular disorders, which include problems with muscles, peripheral nerves, or the communication between them. Muscle atrophy (loss), muscle weakness, and sensory disturbance (such as tingling and numbness) are the most common outcomes of this. Depending on the type, neuromuscular disorders can also cause other symptoms.

What types of neuromuscular disorders are there?

Based on the area of dysfunction, neuromuscular disorders can be divided into multiple subgroups, each of which includes a variety of conditions.

Any condition that alters the composition and/or functionality of any part of your neuromuscular system is referred to as a neuromuscular disorder. This includes:

•  Anterior horn cells

• Dorsal root ganglia and other nerve roots

• Plexuses, such as the lumbosacral and brachial plexuses

• Peripheral nerves

• Neuromuscular connection

• Muscles fibers

Anterior horn cells Conditions

In particular, motor neurons found in the grey matter of your spinal cord are called anterior horn cells. They are necessary for your skeletal muscles to move. Your muscles become weak as a result of denervation, or a lack of nerve supply, brought on by the death of these cells.

Anterior horn cell diseases include:

•  Amyotrophic lateral sclerosis (ALS, or Lou Gehrig’s disease)

•  Atrophy of the spinal muscles

•  Kennedy's disease, also known as spinal-bulbar muscular atrophy (SBMA)

•  Polio

Disorders of the plexus (plexopathies)

The nerves may intermingle to form a complex network or plexus, shortly after they emerge from your spine at various spinal levels. Your upper limbs contain a plexus known as the brachial plexus. Another is the lumbar or lumbosacral plexus, which is located in your lower limbs.

These plexuses could sustain injuries from trauma, compression, or even inflammation, among other sources. The afflicted limb may experience pain, tingling numbness, and weakness as a result.

Nerve roots Conditions

The short branches of a spinal nerve are called nerve roots. Along the length of your spine, between each vertebra (spine bone segment), spinal nerves leave your spinal cord. Motor and sensory nerve root fibers are found in every spinal nerve. Nerve fibers found in motor nerve roots transmit commands from your brain and spinal cord to your muscles via peripheral nerves.

In various parts of your body, pain, numbness, and tingling may result from surrounding tissues pressing on nerve roots. We refer to this as radiculopathy. Muscle weakness results from compression of the motor nerve roots.

Depending on where the pinched nerve is located along your spine, there are various kinds of radiculopathies:

• Cervical radiculopathy of the neck

• Upper back to middle (thoracic radiculopathy)

• Low back (lumbosacral radiculopathy or lumbar)

Conditions peripheral nerves

The term "peripheral neuropathy" refers to a broad category of nerve disorders that impact any peripheral nerves that are not part of the brain or spinal cord. There are numerous varieties and causes. These conditions fall under the even more general category of neuromuscular disorders because you cannot move your muscles without the healthy operation of peripheral nerves.

Only a portion or the majority of your body may be impacted by peripheral neuropathies. The areas of your limbs that are most distant from your core, particularly your hands and feet, are impacted by the most prevalent type of peripheral neuropathy.

Peripheral neuropathies can include those associated with:

• Diabetes

• Disorder of alcohol use

• Malnutrition

• Amyloidosis

• Charcot-Marie-Tooth disease is one example of an inherited or genetic cause.

• Guillain-Barré syndrome and chronic inflammatory demyelinating polyneuropathy (CIDP) are examples of autoimmune or inflammatory causes.

• Toxic exposures due to toxic chemicals, like cleaning fluids or pest killers.

Neuromuscular junction Conditions 

A neuromuscular junction (NMJ) is a synaptic connection (synapse) that occurs between a muscle and the end of a motor nerve. Acetylcholine is a molecule that motor nerves release across the synapse to communicate with the muscle. Some neuromuscular junction disorders are caused by problems with this communication.

The following are the primary conditions affecting the NMJ:

• Botulism

• LEMS, or Lambert-Eaton myasthenic syndrome

• Gravis myasthenia.

Muscles Conditions

Skeletal muscles, or the muscles that attach to your bones, are directly impacted by myopathies. Your muscles become weak as a result of these diseases' attacks on muscle fibers. Myopathies come in various varieties. Some can be developed later in life, while others are genetic or inherited and are present from birth.

Direct muscle injuries, such as a muscle tear, strain, or bruise, are not included in myopathies.

 Muscular dystrophy

The term "muscular dystrophy" describes a collection of over 30 hereditary (inherited) disorders that impair muscle function. Among the forms are:

• DMD, or Duchenne muscular dystrophy. The most prevalent kind is this one

• BMD, or Becker muscular dystrophy

• Dystonia myotonica

• OPMD, or oculopharyngeal muscular dystrophy

Inflammatory and autoimmune myopathies

 Conditions known as inflammatory and autoimmune myopathies are brought on by problems with your immune system and impair muscle function.  Among the examples are:

•  Dermatomyositis

•  Polymyositis

•  Necrotizing myopathy mediated by the immune system

Additional myopathies

Other myopathies are associated with:

• Electrolyte imbalances: Muscle problems can result from electrolyte imbalances such as hyperkalemia (high blood potassium) and hypercalcemia (high blood calcium).

• Hormone interference with muscle function results in endocrine myopathies. For instance, problems with your thyroid, parathyroid glands, or adrenal glands may cause this.

• Metabolic myopathies: These disorders are brought on by problems with the genes that code for the enzymes your muscles require. Lipid storage disorders and glycogen storage diseases are two examples.

• Muscle mitochondria, which are the cells' energy-producing organelles, can develop defects that lead to mitochondrial myopathies.

• A collection of hereditary neurological conditions is known as periodic paralysis. They include times when your muscles weaken, become slack, and lose their ability to contract.

• Toxic myopathies: These occur when a medication or toxin alters the structure or function of muscles.

What symptoms of neuromuscular disorders are present?

Different types of neuromuscular disorders have different symptoms. However, generally speaking, symptoms related to muscles can include:

• Muscles weakness 

• Loss or atrophy of muscles

• Cramps, spasms, or twitches of the muscles (fasciculations)

• Pain in the muscles

• Spasticity

• Walking difficulties

• Problems with balance and coordination

• Eyelids or other facial features that droop

Speaking difficulties brought on by weakness in the tongue or other facial or oral muscles (dysarthria).
Weakness of the throat (pharynx) muscles that causes dysphagia, or difficulty swallowing.
breathing difficulties brought on by weak diaphragm muscles.

Other signs and symptoms could be:

• Fatigue

• Numbness

• Paresthesia is the term for tingling or other unusual sensations

Causes:

The causes of neuromuscular disorders are numerous. However, some of them are inherited. This indicates that either a genetic mutation (change) occurred at random or that you inherited your genes from your biological parents. A single gene error or multiple gene errors can cause a neuromuscular disorder.

Autoimmune diseases include certain neuromuscular conditions. Others are brought on by inflammation, exposure to toxins, nutritional or metabolic disorders, or injuries. Sometimes the cause is unknown.

Diagnosis:

Your doctor will inquire about your symptoms, medications, and family and medical history. A neurological examination will follow a general physical examination. This particular kind of physical examination aids in detecting symptoms of conditions impacting your brain, spinal cord, and peripheral nervous system, which includes your muscles.

For additional assessment, your healthcare provider might recommend that you see a neurologist. The following additional tests aid in the diagnosis of neuromuscular disorders:

• Your skeletal muscles and the nerves that regulate them are assessed for health and function using electromyography (EMG).

• Nerve conduction test: This test assesses how well your peripheral nerves are functioning.

• Blood tests: These tests can look for several things, such as autoimmune condition markers and abnormalities in enzymes.

• Imaging tests: An MRI, CT scan, or neuromuscular ultrasound are examples of tests that can "see" any problems with your brain, spinal cord, or nerves.

• Muscle biopsy: For a pathologist to examine your muscle tissue under a microscope for anomalies, a tiny sample must be taken.

• Certain genetic neuromuscular disorders can be confirmed by genetic testing

How do neuromuscular disorders get treated?

The way that different types of neuromuscular disorders are treated varies greatly. Generally speaking, there is no known cure for many neuromuscular conditions. However, there might be therapies and treatments that can lessen the symptoms and halt or slow the progression of the illness. Your course of treatment could include:

• Medications

• Occupational and physical therapy

• Speech therapy

• Nutritional therapy

• Assistive technology to improve mobility

• Procedures, such as surgery

For a neuromuscular disorder, your primary healthcare provider will probably be a neurologist, including a neuromuscular specialist. But you might require extra providers based on the type. They might consist of:

• Occupational and physical therapists.

• Rheumatologists

• Respiratory therapists and pulmonologists

• Pathologists

• Surgeons

• Orthopaedists

• Pathologists of speech and language

• Nutritionists

• Psychologists

• Social workers

References:

• Morrison BM. Neuromuscular Diseases (https://pubmed.ncbi.nlm.nih.gov/27704495/). Semin Neurol. 2016 Oct;36(5):409-418. Accessed 2/20/2024.

• Omar A, Marwaha K, Bollu PC. Physiology, Neuromuscular Junction (https://www.ncbi.nlm.nih.gov/books/NBK470413/). 2023 May 1. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Accessed 2/20/2024.

• DiSabella MT, Castillo-Pinto C. Neurologic Disorders. In: Dietzen D, Bennett M, Wong E, Haymond S, eds. Biochemical and Molecular Basis of Pediatric Disease. 5th ed. Academic Press; 2021: 1023-1056.

• Approach to Patients with Neuromuscular Disease. In: Amato AA, Russell JA, eds. Neuromuscular Disorders. 2nd ed. McGraw Hill; 2016.

• Merck Manual: Consumer Version. Nerve Root Disorders (https://www.merckmanuals.com/home/brain,-spinal-cord,-and-nerve-disorders/peripheral-nerve-and-related-disorders/nerve-root-disorders). Last modified 9/2022. Accessed 2/20/2024.