Muscle diseases originate from the muscle cells. CC BY-SA 3.0, wikimedia.org

Definition

Muscular diseases are attacking muscle cells so that the strength is weakened. Women, men and children of all ages can be attacked. The different muscular diseases are distinguished by different symptoms, findings on examination, treatment and prognosis.

Musculoskeletal diseases are distinguished from nerve diseases that can also cause reduced muscle function, but the cause is damage to the nerves that should activate the muscles. Examples of such nerve diseases are Multiple sclerosis (MS), Myastenia gravis, Amyotrophic lateral sclerosis (ALS) and Parkinson's disease.

Stiffness, muscle aches and other rheumatic disorders often increase with age and may be part of the normal aging process. Please read more about Aging and rheumatic symptoms here

Different muscle disease

• Hereditary Muscular dystrophies are discussed on separate pages, please read more here
• Myositis with rheumatic inflammation of the muscle cells (inflammatory myopathies) is discussed in more detail here
• Electrolyte disturbances in blood and tissue with too high or too low levels of potassium, calcium, or magnesium can occur in many diseases or as a side effect of various drugs, especially diuretics or some type of blood pressure medication
• Metabolic diseases that glycogenosis-, lipidosis diseases cause too much storage of glycogen or lipids in the muscles
• The mitochondria ("cells' power station") can be affected (mitochondrion disease). Often there are hereditary causes
• Too low or too high values ​​of some hormones give typical muscle symptoms (endocrine myopathy) seen by endocrine diseases. An example is too low thyroid function («Low metabolism» hypothyroidism)
• Infections (viruses, bacteria, parasites) may give some severe muscle aches
• Cancer is unusual in muscles, but sarcomas which can occur in different types of connective tissue can also attack muscles
• Drugs like cholesterol lowering Statins sometimes cause muscle disease
• Muscular overload, poisoning or physical injury to muscles may trigger rhabdomyolysis in which large amounts of muscle cells are suddenly injured
• By Polymyalgia rheumatica people are affected by the age over 50. The reason for rapidly developing stiffness and pain is unknown, but one finds inflammations in joints and tendon attachments outside the muscles themselves. More about polymyalgia rheumatica here
• Fibromyalgia causes chronic muscle pain. The triggering cause, however, is primarily not found in the muscles. Please read more about fibromyalgia here

Diagnosis

The history of illness is important for distinguishing different types of muscle disease.

• Muscle disease in the immediate family, age at onset of symptoms, rapid (days) or slow (weeks-years) development is important.
• Prior travel abroad, injury, medication and alcohol consumption are also important information

By examining the physician may evaluate if the muscles have normal size and strength, if they are painful or tight. Symptoms from other organs are also investigated

• In blood tests are creatine kinase (CK) elevated by muscle dystrophy, myositis and especially in rhabdomyolysis. CK is an enzyme which originates from muscle cells. The higher the rate in CK, the more widespread muscle injury may be assumed to be present. After physical exercise and corresponding strain, the values ​​also rise, but they fall to normal after a few days. Electrolyte and hormone disorders are also detected in blood samples
  • In myositis, unnormal results of antinuclear antibody (ANA) and associated subgroups are often found. In some cases, these subgroups may show increased risk of development of particular complications. An example is anti-Jo-1 antibody that indicates closer investigation of the lungs
• By electromyography (EMG) og neurography signals from muscles and nerves can show different responses, depending on the underlying cause of the disease, but the tests alone are insufficient to provide a safe diagnosis
• MRI examination of attacked muscles can help differentiate the various muscular diseases. In addition, MRI changes may indicate areas where it is appropriate to take tissue samples (biopsy) from
• Tissue (biopsy) from the attacked muscle is always an important study in the investigation.
  • By microscopic examination and other tests through the tissue sample one can distinguish hereditary myopathies from myositis, rhabdomyolysis and metabolic muscle diseases
• In the event of suspected hereditary muscular dystrophy or metabolic muscle disease, genetic consulting and associated tests can de done

Incorrect diagnosis (similar conditions, differential diagnoses)

• Fibromyalgia og myalgia (muscle pain) are pain in muscles that reduce function, but without inflammation or other disease in the muscle cells. Women are most commonly affected
• Polymyalgia rheumatica attacks older people (over the age of 65 years). There are clear evidence of inflammation in tests, but not in the muscle cells itself
• Disease of the nervous system, which results in reduced muscle function occur in
  • Multiple Sclerosis (MS)
  • Myastenia gravis
  • Amyotrophic lateral sclerosis (ALS)
  • Parkinson's disease

Treatment

To provide proper treatment, diagnosis of type of muscle disease is essential. The treatment is described under the individual diagnoses.

Prognosis

The prognosis are very different between the various diseases, in part, also depending on the response and tolerance of the treatment. For more information, see articles about the different diseases.

Specialists

• The hereditary muscular dystrophies are investigated and usually treated by pediatricians and in adult age by neurologists
• Myositis is within the field of rheumatology
• Metabolic and hormonally-induced muscle diseases are most commonly handled by endocrinologists
• Other types of muscle diseases are assessed and followed by other specialists or general practitioners, depending on the severity. If necessary, close collaboration between a specialist, a GP, possibly other therapists and the patient is always important

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