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.

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

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.