In all countries that collect comprehensive disease statistics Myositis falls within the definition of being A RARE DISEASE. Myositis has consistently shown in overseas studies to have an incidence of 5 to 10 people per 1,000,000 of population for each of the three adult diseases across all age groups above 18 years old. The juvenile form, defined as 0 to 18 years of age, has an incidence of 3 to 4 young people per 1,000,000 of population.

Typical Early Signs

  • Muscle weakness in thighs and shoulders
  • Unexplained general tiredness and fatigue
  • Difficulty standing up from a seat or floor
  • Difficulty climbing stairs
  • Falling down unexpectedly
  • In cases of IBM, weak grasping of objects and difficulty swallowing
  • In cases of DM, a reddish purple skin rash.
  • In cases of Necrotising Myositis there may also be severe pain, swelling, rash/infection, temperature, blood pressure changes


The underlying cause of all the inflammatory muscle diseases is unknown. They are classified as autoimmune diseases because the primary activity is the body’s immune system attacking its own tissue. The exception to this is Inclusion Body Myositis (IBM) where the autoimmune activity is now generally regarded as a secondary response by the immune system to remove diseased cells from within the muscles. Thus IBM is not a classical autoimmune disease but is still by definition a “myositis” condition.

In rare cases there may be a drug interactions/side effects, bacterial, fungal, parasitic or viral involvement eg Necrotising Myositis.


Copyright 2016
The Myositis Association-Australia Incorporated