With advances in autoantibody discovery and description of novel myositis subsets, polymyositis (PM) has become a controversial entity that is now considered to be uncommon. Before diagnosing individuals with polymyositis, physicians need to carefully eliminate disease mimickers such as muscular dystrophies and other myositis subsets such as necrotizing myopathies. Polymyositis is characterized by chronic muscle inflammation and weakness as well as certain muscle biopsy features. As with other types of myositis, there is no known cause or cure for polymyositis. There are, however, treatments that are successful in managing symptoms.

Polymyositis signs and symptoms

The following are the most common signs and symptoms of polymyositis:

  • Weakness in the muscles closest to the center of the body, like the shoulders, forearms, hips, thighs, neck, and back
  • Muscle pain
  • Falling and difficulty getting up from a fall
  • Shortness of breath and/or chronic dry cough
  • Difficulty swallowing (dysphagia)

Muscle weakness

Muscle weakness usually happens over days, weeks, or months. It can affect your ability to walk, run, and lift yourself up after a fall. The weakness typically begins with muscles closest to and within the trunk of the body, such as the muscles of the neck, shoulders, hips, and back.

For some, that weakness can spread to other parts of the body. Polymyositis can affect muscles all over the body, and some patients can feel weakness in muscles far from the trunk, for example in the hands and fingers. Others with polymyositis may also experience muscle pain, breathing problems, and trouble swallowing as the muscles in the digestive tract and chest wall can also be affected.

If you are experiencing any of these polymyositis symptoms, we encourage you to talk to your doctor to begin the diagnosis process, which often includes a muscle biopsy to distinguish the muscle weakness from other muscular disorders. Since polymyositis is a rare disease, many physicians may not be familiar with the signs and symptoms. If you’re struggling to find an accurate diagnosis, visiting a specialist can help.

Revised April 2025 by Valérie Leclair, MD, PhD – rheumatologist, research scientist, and TMA medical advisor