Everything about Neuromuscular Disorders – Types, Causes & Symptoms

The neuromuscular system of the human body comprises the muscles and the nerves that transmit signals helping muscle movements (peripheral nervous system). Consequently, any abnormality in the neuromuscular system can lead to neuromuscular disorders causing numbness, weakness or even paralysis of different body parts.

In this article, you will find the different categories and types of neuromuscular disorders and their symptoms and progression.

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What Is Neuromuscular Disorder?

Neuromuscular disorders comprise a wide-ranging category of diseases that affect the peripheral nervous system, consisting of motor and sensory nerves connecting the brain and spinal cord to the rest of the body. These disorders are predominantly characterised by progressive muscle weakness, wasting and function loss, along with other conditions.

These conditions are primarily genetic or due to problems arising in the immune system. Based on the cause and nature of the condition, neuromuscular disorders can of several types, which are classified under four broad categories:

Muscular dystrophies
Myopathies
Neuromuscular junction disorders (myasthenic conditions)
Motor and/or sensory neuropathies

What Are the Types of Neuromuscular Disorder?

The 10 most common types of neuromuscular disorders include the following:

1. Amyotrophic Lateral Sclerosis (ALS)

Also known as Lou Gehrig’s disease, it is a life-threatening disorder that has no cure. This condition brings about the stiffness of muscles, affecting all voluntary muscles. This is because the neurons that transmit signals from the brain to the upper and lower body parts die and their function ceases, ultimately leading to the failure of all body functions.

Age at Onset: ALS can affect people of an age group but is most common between 40 and 70 years of age.
Symptoms

Early Symptoms:

Muscle cramps in arms, legs, shoulders, or tongue
Stiffness of muscles (spasticity)
Muscle cramps
Muscle weakness affecting the limbs or diaphragm
Slurred or nasal speech

Severe Symptoms:

Difficulty chewing or swallowing
Breathing difficulty
Paralysis
Rate of Progression: The progression rate varies from person to person. It may range from 1-3 years to 5-10 years, the latter being rare.
Life Expectancy: The average life expectancy is 3 years. However, about 20% of the people live up to 5 years, and 10% live up to 10 years.

2. Duchenne Muscular Dystrophy (DMD)

DMD is a genetic condition affecting muscles leading to progressive wasting. It mainly occurs in males and affects females on rare occasions.

Age at Onset

Between 2-6 years.

Symptoms
Muscle weakness mainly in upper arms, pelvis and upper legs.
Frequently falling down
Trouble in running
Trouble learning in some cases
Wasting of voluntary muscles
Rate of Progression

The progression rate is rapid.

Life Expectancy: Affected people survive only till their 20s or 30s.

3. Congenital Myopathy

It is an inherited genetic condition that occurs from birth, affecting all voluntary muscles of the body, including the ones associated with swallowing and breathing.

Age at Onset

Occurs right from birth.

Symptoms
Feeding and breathing problems
Weak bones (osteopenia)
Poor skeletal conditions, such as sideways curvature of the spine (scoliosis)
Hip problems
Rate of Progression

Progression is slow but causes shortened life span depending on the type and severity of the condition.

4. Charcot-Marie-Tooth disease

Charcot-Marie-Tooth (CMT) disease is a condition that affects the nerves. It is an inherited disorder that causes anomalies in the nerves mainly related to your feet, legs, and rarely hands and arms. It affects both sensory and motor nerves.

Age at onset

Onset age is typically between 5 to 25 years.

Symptoms
Loss of sensation
Joint contractures
Muscle weakness and atrophy
Poor balance and coordination
Loss of fine motor movements in case of affected hands
Scoliosis
Rate of Progression

The progression rate is gradual.

Life Expectancy: Life expectancy is not affected.

5. Emery–Dreifuss Muscular Dystrophy

Emery–Dreifuss muscular dystrophy is one of the other heritable neuromuscular diseases causing progressive impairment of muscles. It is mainly caused by genetic mutation and affects skeletal muscles used for movement as well as cardiac muscles used for heart pumping.

Age at onset

The average age of onset is about 10 years.

Symptoms
Joint contractures
Muscle weakness in shoulders, shin, etc.
Heart complication
Rate of Progression

The rate of progression is gradual.

Life Expectancy: People developing cardiac issues due to muscle failure have an increased chance of sudden death.

6. Facioscapulohumeral Muscular Dystrophy

This type of muscular dystrophy mainly causes muscle weakness and atrophy in the facial muscles, scapula and upper arm (humerus), as indicated in its name.

Age at Onset

Generally, symptoms appear in late childhood to early adulthood.

Symptoms
Weakness in facial muscles
Weakness in the shoulder (mainly shoulder blades)
Scoliosis
Vision loss due to structural changes in the blood vessels (Coats disease)
Pain or swelling of joints and muscles
Weakness in the hips, abdominal region or upper legs
Rate of Progression

Slow progression with periods of rapid degeneration

Life Expectancy: Life expectancy is not shortened, but the severity may vary from person to person.

7. Myasthenia Gravis

Myasthenia gravis is an autoimmune disease characterised by inflammation throughout the body. This condition occurs when the immune system attacks the body's own acetylcholine receptors, reducing muscle contractions.

Age at Onset

It can occur at any age but is more frequent from 40 to 60 years.

Symptoms
Weakness in arms, legs, eyes and face
Double vision or droopy eyelids
Trouble swallowing or in speech
Difficulty in breathing
Rate of Progression

The progression rate is slow

Life Expectancy: Life expectancy is not affected, and people can continue living active life for years.

8. Multiple Sclerosis

Multiple sclerosis, also known as MS, occurs when the patient's immune system attacks the neuroprotective myelin sheath. Myelin is made up of fatty tissue that surrounds the nerve cells. The damage and resulting scar tissue around nerve fibres prevent impulses from being conducted from the brain, preventing nerves from functioning correctly.

9. Oculopharyngeal Muscular Dystrophy (OPMD)

Oculopharyngeal muscular dystrophy is a hereditary condition and an autosomal dominant disease. It affects the skeletal muscles (mainly ocular and pharyngeal muscles) and the proximal extremities.

Age at Onset

This condition has a late onset, usually between 40 to 70 years.

Symptoms
Droopy eyelids
Facial muscle weakness
Leg and arm weakness
Choking or swallowing issues (dysphagia), especially for dry foods
Shrinking of the tongue
Saliva pooling
Rate of Progression

The progression rate is slow.

Life Expectancy: Life span is not affected.

10. Spinal Muscular Atrophy (SMA)

This type of neuromuscular disorder is a hereditary condition produced by a genetic mutation that damages the protein required for regular motor neuron activity. There are various different types of SMA, with varying onset ages.

Age at Onset

Onset ages range from childhood and adolescence to maturity.

Symptoms
Problems in swallowing food
Muscle weakness
Inability to stand or walk
Numbness in certain parts
Diminished muscle tone (Hypotonia)
Respiratory issues
Involuntary contractions or muscle twitching
Scoliosis
Reduced or absence of deep tendon reflexes
Rate of Progression

The rate of progression is slow.

Life Expectancy: Life expectancy may get affected, especially if the respiratory muscles are affected.

Neuromuscular disorders consist of a wide range of disorders that affect the muscles and functions of different parts of your body. While only some of these are treatable, all of them can be managed by timely medical intervention. Therefore, if you notice any of these common symptoms, do consult a professional immediately.

Frequently Asked Questions

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Do all neuromuscular disorders have common symptoms?

Most neuromuscular diseases have a few common symptoms, such as muscle weakness, wasting, inability to move or numbness of limbs, as they are mainly caused by peripheral nerve damage. However, depending on the disease site and the patient's age, symptoms may differ.

Are neuromuscular diseases treatable?

Depending on the type and severity, treatment and curability of neuromuscular disorders may vary. Some may not be treatable; however, with advanced treatment and early diagnosis, mobility and quality of life may be improved.