Myopathy (disorders of muscles)

What is myopathy?

Myopathy is the medical term for a group of conditions that damage your skeletal muscles, the muscles attached to your bones that let you move. Unlike a nerve condition, the fault sits within the muscle fibres themselves, and it typically causes weakness alongside symptoms such as pain, cramping or stiffness.

What are the symptoms of myopathy?

Of all the possible signs, muscle weakness is the one doctors rely on most. It usually affects muscles closest to your trunk first, such as your shoulders, upper arms, hips and thighs, making certain everyday movements harder before your hands or feet are affected.

• weakness in your shoulders, upper arms, hips or thighs
• muscle pain, cramping or stiffness
• feeling tired quickly, or generally low on energy
• difficulty with everyday tasks such as dressing, washing or rising from a seated position
• trouble climbing stairs or lifting things above your head
• joint stiffness or tightness, since muscles that aren't moving properly can make joints harder to move too
• in some types, difficulty swallowing or speaking clearly.

Some types of myopathy cause the opposite of wasting: muscles, particularly the calves, can look unusually large even as they weaken, because muscle tissue is gradually replaced by fat and fibrous tissue. After very intense exercise, dark or cola-coloured urine can be a sign of muscle breakdown and needs prompt medical attention.

What causes myopathy, and who is at risk?

Myopathy falls into two broad groups. Inherited myopathies are ones you're born with, caused by a faulty gene passed down from a parent, and these tend to progress slowly over years. Acquired myopathies develop later in life, brought on by something separate from your genes.

• an autoimmune condition, where your immune system mistakenly attacks your own muscle tissue
• a hormone problem, such as thyroid or adrenal gland disease
• an infection, caused by bacteria, a virus, a parasite or a fungus
• certain medicines or alcohol
• a serious illness requiring intensive care, which can itself cause muscle weakness
• a tumour elsewhere in the body triggering a muscle reaction.

Age of onset gives some clues to the cause. Myopathy present from birth is almost always inherited. In children, new-onset myopathy is more likely to involve an infection or a hormone-related cause. In adults, the same acquired causes apply, alongside toxic and critical-illness myopathies that are less common earlier in life.

Are there different types of myopathy?

Inherited types

• Mitochondrial myopathy: caused by a fault in the energy-producing structures inside your cells, which can also affect your heart, brain or gut.
• Congenital myopathy: usually shows up in babies or young children as developmental delay with crawling or walking, and tends not to worsen much over time.
• Muscular dystrophy: muscle tissue gradually breaks down and weakens over time.
• Metabolic myopathy: causes bouts of weakness, often triggered by exercise or exertion.

Acquired types

• Inflammatory (autoimmune) myopathy: covers conditions such as dermatomyositis, where weakness is accompanied by a reddish rash on the face, knuckles and elbows, and polymyositis, which causes weakness without the rash. Both usually respond to steroids or medicines that calm the immune system.
• Inclusion body myositis: a slowly progressive form causing weak grip and difficulty straightening the knees, for which no fully effective treatment currently exists.
• Toxic myopathy: triggered by a medicine or by alcohol.
• Endocrine myopathy: linked to a hormone imbalance, most often affecting the thyroid, parathyroid or adrenal glands.
• Infectious myopathy: follows an infection, caused by bacteria, a virus, a parasite or a fungus.
• Critical illness myopathy: develops during a stay in intensive care.

How is myopathy diagnosed?

Diagnosis starts with a detailed conversation about your symptoms and family history, followed by a physical examination that checks your muscle strength and reflexes.

• blood tests, particularly creatine kinase (CK), an enzyme that leaks out when muscle is damaged; other markers such as aldolase may also be checked
• eMG (electromyography) and nerve conduction studies, which test the electrical activity in your muscles and help confirm whether a problem lies in the muscle rather than the nerve
• an MRI scan, to look at your muscles in more detail and help guide where a biopsy should be taken from
• a muscle biopsy, where a small sample of muscle is removed and examined under a microscope
• genetic testing, particularly where an inherited myopathy is suspected.

A raised CK result alone doesn't confirm myopathy, since things like recent injury, strenuous exercise, viral infections and even certain medicines can raise it too. Your doctor will weigh up your results alongside your symptoms and examination findings before reaching a diagnosis.

How is myopathy treated?

Non-surgical treatment

• physiotherapy, to help maintain strength, flexibility and mobility, and to reduce the risk of falls
• cccupational therapy, to help you manage everyday tasks and stay independent
• hydrotherapy, electrotherapy and structured exercise or stretching programmes
• steroids or immunosuppressant medicines, for inflammatory and autoimmune types
• stopping or changing the medicine responsible, for toxic myopathy, only ever under medical guidance
• antiretroviral therapy, where HIV is the underlying cause
• treating the underlying hormone problem or infection, for endocrine or infectious myopathy
• a balanced diet and staying appropriately active, particularly for some metabolic myopathies
• mobility aids, braces or other equipment to support weaker muscles and joints.

Surgical treatment

Surgery isn't a routine or first-line treatment for myopathy. It's mentioned in the source material only in general terms, as an option that may occasionally be used for specific complications rather than for myopathy itself, so ask your care team whether it's relevant to your particular situation.

When should I see a doctor?

• muscle weakness, pain, cramping or stiffness that's new, persistent or getting worse
• weakness that's starting to affect everyday tasks, such as dressing, climbing stairs or swallowing
• dark or cola-coloured urine after intense exercise, which can be a sign of muscle breakdown and needs prompt medical attention.