What Is Myopathy?

Overview

Muscles are soft tissues that are made up of fibres that help us do different types of activity. The 3 types of muscle tissues are skeletal (these muscles support the bones, tendons, and ligaments, and they help in voluntary movements), cardiac muscles (these muscles help in pumping the blood from the heart), and smooth muscles (these muscles lines the inside of the organs like bladder, stomach, and intestines).

Myopathy is a disease that affects the muscles which control the voluntary movements of the body. The disease affects the skeletal muscles, attacking the muscle fibre and weakening them. Only the muscles are affected without affecting the nervous system.

Myopathy can be genetic (inherited), which means passed on by parents to children, and it can be acquired later in life from any medical disorders, medications, or any other possibilities.¹

Types of myopathy

Myopathy can be classified as inherited or acquired myopathies according to their causative factor.

Inherited myopathies

Inherent myopathy is the condition in which an abnormal gene mutation is passed from parents to children, causing the disease. The different types of inherited myopathies are: 

• Congenital myopathy often starts in early childhood and may not appear in teenage or adulthood. This affects all the muscles, causing weakness, and often, they are not progressive.
• Mitochondrial myopathy: mitochondria are the energy-producing parts of the cell, where muscle weakness also affects the other organs like the heart, brain and gastrointestinal tract. It can also cause muscle weakness and neurologic difficulties such as seizures, imbalance and deafness
• Metabolic myopathy: metabolism is the chemical reaction in the body’s cells that changes food into energy. Metabolic myopathies occur when defects in genes cause improper levels of enzymes, and the affected muscles cannot convert food into energy, which leads to improper functioning of the muscles.
• Muscular dystrophy: a progressive degeneration of muscle tissue due to abnormal structural support proteins being present. Some of the muscular dystrophies are:
  • Duchenne muscular dystrophy (DMD) is the most common type of X-linked recessive condition, which appears in early childhood and progresses rapidly. New symptoms are common in Duchenne muscular dystrophy.
  • Becker’s muscular dystrophy (BMD) is less common and less severe than other muscular dystrophy. BMD is an X-linked recessive disorder due to a mutation in the dystrophin gene that leads to progressive muscle degeneration and muscle weakness. The onset of symptoms is late when compared to Duchenne muscular dystrophy²
  • Facioscapulohumeral muscular dystrophy (FSHD) is a common adult muscular dystrophy that is divided into 2 types according to its genetic mutation. Both types show asymmetrical and progressive muscle weakness affecting the face, shoulder, and arms initially and then affecting the lower extremities³
  • Limb-girdle muscular dystrophy (LGMD) is a group of rare inherited disorders which affects mainly the muscles around the shoulder and hip causing muscle weakness. Some other muscles affected are heart muscles

Acquired myopathies

These develop later in life and can be due to any medical disorders, infections, medications, or other possibilities. Some of the conditions of acquired myopathies are: 

• Autoimmune myopathy: autoimmune diseases arise when the body attacks its healthy cells instead of bacteria or any viruses. Some diseases are:
  • Polymyositis and dermatomyositis are connective tissue diseases characterised by muscle inflammation. Proximal myopathy causes weakness in proximal muscles. Dermatomyositis causes muscle weakness and skin rashes
  • Systemic lupus erythematosus is a multi-system autoimmune disease that can occur at any age. It is prone to relapse and remission of the disease
  • Rheumatoid arthritis (RA) is a common chronic inflammatory autoimmune disease where it causes morbidity, including pain, and disability
• Toxic myopathy: occurs when toxins or medications affect muscle function. Alcohol, tobacco, and such products can affect the muscles, and medications such as corticosteroids, antivirals, and omeprazole can affect muscle function⁴
• Endocrine myopathy: occurs due to hormonal imbalance and this affects muscle function. Some hormonal disease conditions which include endocrine myopathy are hypothyroidism, hyperthyroidism, Addison’s disease, and Cushing syndrome
• Infectious myopathy: occurs when infections affect muscle function. These include Lyme disease, viral infections (HIV, influenza), bacterial infection, parasitic infection, and fungal infections
• Electrolyte imbalance: this can occur in disease conditions like hypokalemia (low blood potassium), hyperkalemia (high blood potassium), and hypermagnesemia (high blood magnesium), where the high and low level of electrolytes interferes with muscle function
• Critical illness myopathy: occurs when the person is in an intensive care unit or is bedridden for a long time or due to the medications used during the care like muscle relaxants, can cause critical illness myopathy which affects the limbs.⁵

Causes of myopathy

Anyone can get myopathy, but the chances of the person being prone to myopathy include: 

• Family history: there is an increased chance of risk of inheriting an abnormal gene if anyone in the family has myopathy
• Sex: people assigned male at birth (AMAB) are more prone to certain myopathies as they are carried mainly by the X chromosome. Other forms of myopathy carried by the chromosomes affect all the sexes equally
• Having an autoimmune disease, a metabolic or an endocrine disorder
• Prolonged usage of certain medicines or toxins

Signs and symptoms

Myopathy symptoms occur according to the area affected but they have certain common symptoms such as: 

Muscle weakness

• Muscle cramps
• Fatigue
• Delayed motor movement
• Muscle stiffness
• Muscle wasting around shoulders and hips
• Difficulty in performing day-to-day activities

Diagnosis of myopathy

Healthcare personnel will ask about the patient’s medical and family history. At first, they will conduct a physical examination to check the skin for rashes, and check the reflexes, balance and sensation. The other tests are blood tests that screen for

• Muscle enzymes such as creatine kinase
• Electrolytes like sodium, magnesium, potassium, calcium and phosphorus
• Autoimmune diseases, such as antinuclear antibodies (ANA), rheumatoid factor and c-reactive protein
• Thyroid hormone

Electromyography (EMG): this is used to diagnose the injuries and conditions that affect the muscles and nerves. This test is used along with nerve conduction study.

Magnetic resonance imaging (MRI): this helps in assessing the complications and neurological disease.

Muscle biopsy: during this procedure, the healthcare professional removes the small muscle tissue and they are examined under a microscope.

Genetic tests: genetic testing helps in finding defective genes and helps in reaching the diagnosis.

Treatment and management

Treatment of myopathy is given according to the presented symptoms and thus will vary by patient. Most of the treatment includes physical therapy, occupational therapy and exercise. Patients are consulted by a rheumatologist or neurologist.

• In the case of autoimmune-related myopathies the main aim is to decrease the inflammation using immunosuppressant drugs and corticosteroids
• In the case of inherited and genetic myopathies there is no specific treatment given, only the symptoms are reduced. Genetic counselling is given to patients and their families
• In case of acquired myopathies the underlying disease condition is treated
• Surgery in cases where walking is difficult, tendon release surgery
• Physiotherapy
• Proper diet and exercise are given in case of endocrine myopathy, which helps in reducing the symptoms and improving the health

Prevention and risk reduction

• Genetic counselling: this helps people to understand and identify the risk of getting myopathy
• Avoiding the usage of certain medications
• Following proper diet and exercise
• Proper regular health check-ups

FAQs

What are the symptoms of myopathy?

Symptoms of myopathy change according to the area affected. But some common symptoms are muscle weakness, stiffness, cramps and muscle wasting.

What is the main cause of myopathy?

Myopathy can be caused by any medical conditions, usage of certain medicines or drugs, and hereditary.

Can myopathy be treated?

In certain cases of myopathy, it can be treated completely and in certain cases, the symptoms are reduced and can ease the suffering of the patient.

Which blood test helps in identifying myopathy?

Blood tests detect elevated levels of the enzyme creatine kinase, which indicates the person has inflammatory myopathy.

Summary

Myopathy is a disease that affects the muscles which control the voluntary movements of the body. The disease affects the skeletal muscles, attacking the muscle fibre and weakening them. Only the muscles are affected without affecting the nervous system. Myopathy can be genetic (inherited) which means passed on by parents to children and it can be acquired later in life from any medical disorders, medications or any other possibilities. The treatment is given according to the symptoms present. Most of the treatment includes physical therapy, occupational therapy and exercise.